Can Disk Brakes flip you over the handle bars?

[TBerk]

Obviously I would assume they could if you clamp down fast enough.

I ask because I bruised some rib bones this week when I stomped the
front brake and *surprise* I found out later my front rim has a bubble
bend in it from (I guess) a pot hole at some recent time.

Made for a portion of the rim that just wasn't going to get past the
brake pads, not while I was trying to actually use said brakes.

It would seem a better setup would be one unaffected by a slightly
bent rim, or so I wonder.


TBerk
it would have been funny if it hadn't hurt so much at the time

[[email protected]]

The Berk wrote:

> Obviously I would assume they could if you clamp down fast enough.

> I ask because I bruised some rib bones this week when I stomped the
> front brake and *surprise* I found out later my front rim has a
> bubble bend in it from (I guess) a pot hole at some recent time.

> Made for a portion of the rim that just wasn't going to get past the
> brake pads, not while I was trying to actually use said brakes.

> It would seem a better setup would be one unaffected by a slightly
> bent rim, or so I wonder.

http://www.sheldonbrown.com/brandt/over-the-bars.html

> it would have been funny if it hadn't hurt so much at the time

Don't laugh. I wouldn't be so ready to tell all that I used bicycle
brakes in such a clumsy manner. Skilled motorcyclists do nose-down
wheelies at high speed, often crossing the finish line on only the
front wheel. That takes a bit of extra skill. A motorcyclist crashed
fatally yesterday in East Palo Alto doing that.

Jobst Brandt

[[email protected]]

On Apr 30, 10:49 pm, TBerk > wrote:
> Obviously I would assume they could if you clamp down fast enough.
>
> I ask because I bruised some rib bones this week when I stomped the
> front brake and *surprise* I found out later my front rim has a bubble
> bend in it from (I guess) a pot hole at some recent time.
>
> Made for a portion of the rim that just wasn't going to get past the
> brake pads, not while I was trying to actually use said brakes.
>
> It would seem a better setup would be one unaffected by a slightly
> bent rim, or so I wonder.
>
> TBerk
> it would have been funny if it hadn't hurt so much at the time

Disk brakes have more stopping power and any such 'stomp' can result
in a flip, not requiring any irregularities. Due to their design,
recumbents are immune from such a flip.

[DougC]

wrote:
> The Berk wrote:
>
>> Obviously I would assume they could if you clamp down fast enough.
>
>> I ask because I bruised some rib bones this week when I stomped the
>> front brake and *surprise* I found out later my front rim has a
>> bubble bend in it from (I guess) a pot hole at some recent time.
>> ....
>
> http://www.sheldonbrown.com/brandt/over-the-bars.html
>
>> it would have been funny if it hadn't hurt so much at the time

As someone else noted, most recumbents are immune to this
flipping-over-forward problem under hard braking. In my opinion this is
another reason that recumbents may be safer for general use--in that
during a panic stop, the brakes can be applied with wild abandon and
while the bike may slide out and drop the rider sideways, at least it's
not going to flip them over onto their head.... Usually (with any type
of cable-operated brakes) neither wheel will lock up. The LWB recumbent
I have has 160mm BB5 (cable) disk brakes and can't lock either wheel on
clean pavement at all. The RANS Fusion I own isn't that much longer or
lower than a normal upright bicycle; it has 200mm BB7's and won't lock
up or flip over forward either, from a normal riding position, and that
bike basically only has one riding position (standing on the pedals
requires serious effort for anything more than a few moments, and the
pedals are so far forward of the seat that you cannot scoot backwards
off the seat at all). Both these bikes carry about 66% of the weight on
the rear tire normally; that may not be ideal for racing but it seems to
improve safety.

Of course you always get people who claim they can stop an upright bike
perfectly fine,,, but this sounds kinda like when anti-lock brakes first
became common on cars and some people argued that they "didn't need it".
....Which is true in the absolute, you don't /need/ it, but you can't
stop as quickly without it, or with as good of control. Over time the
advantages of not losing directional control in a panic stop became
pretty obvious in repeated studies, and if you brake hard enough to lift
the rear wheel of an upright bike off the ground, then you've pretty
much lost control.

Also if you enter the words {bicycle over bars crash} in Google, you get
back a huge number of results--you still see a lot of people telling
"over-the-bars" stories, which was what safety bikes were supposed to
solve compared to the earlier penny-farthings. If you enter the
words("recumbent bicycle" over bars crash} you get very few, and most of
those aren't discussing such a recumbent crash at all. Much of the
upright-bike results seem to be off-road/MTB stories however, which I
don't consider a "typical" riding situation in terms of safety. When
you're riding off-road you do all sorts of stupid stuff, it's what MTB's
are for. The flipping-forward problem I only consider to be important
with on-road use bicycles.

I don't know that this translates into shorter stopping distances
however. It'd be interesting to compare two bicycles with hydraulic disk
brakes (and speedometers)- an upright MTB and a LWB recumbent--and do a
three-way comparison to see which one can stop quickest from a given
speed. The recumbent, with the rider in the normal (only) riding
position, and the MTB in the normal riding position, and also the MTB
with the rider low, arms locked and scooted backwards off the saddle.

The reason I say "hydraulic brakes" is that the power of cable-operated
disks varies with the cable lengths. The braking power front-to-rear on
an upright bike is a bit disappointing, but the difference on a longer
recumbent can be huge (does anyplace make thicker brake cable & jacket,
that will work with normal brakes? I'd try it...). I'd love to see
results of this kind of testing, but can't be much help as I won't
likely be putting hydraulics on either of my bikes anytime soon.

.....If you *prepare* yourself for braking you can lay on the front brake
of an upright--but that is the exact problem; many people who suffer
these crashes during on-road use are unaware they will have to stop
until it's too late.

>
> Don't laugh. I wouldn't be so ready to tell all that I used bicycle
> brakes in such a clumsy manner. Skilled motorcyclists do nose-down
> wheelies at high speed, often crossing the finish line on only the
> front wheel. That takes a bit of extra skill. A motorcyclist crashed
> fatally yesterday in East Palo Alto doing that.
>

This is called a reverse wheelie, or a "stoppie":
http://www.dirtrodders.com/stoppie.html
Interesting on this page, that the article notes that the front brake
(of a motorcycle) needs to be applied smoothly, or else the front wheel
will simply slide. (I don't have a motorcycle, so I can't play these
sorts of games)
I am informed that it's bad for the fork seals.
There's classic photos on the stuntlife website of one kid attempting a
stoppie--likely not the first time--and his forks crumpling at the
triple clamps and the bike falling onto him (Stuntlife's motto seems to
be something like "Keeping high school overpopulation in check, one
motorcycle rider at a time").
~

[Clive George]

"DougC" > wrote in message
...

> The reason I say "hydraulic brakes" is that the power of cable-operated
> disks varies with the cable lengths. The braking power front-to-rear on an
> upright bike is a bit disappointing, but the difference on a longer
> recumbent can be huge (does anyplace make thicker brake cable & jacket,
> that will work with normal brakes? I'd try it...).

It's why our tandems all have hydraulic brakes. 2 with magura rims, one with
discs.

And tandems also have the "brake as hard as you like, you're not going over
the top" thing :-)

cheers,
clive

[landotter]

On Apr 30, 10:49 pm, TBerk > wrote:
> Obviously I would assume they could if you clamp down fast enough.

Yes, if you don't brace yourself and are unfamiliar with the brake and
grab wildly, any powerful brake can be dangerous--but so can many
things in life. Well adjusted brakes should be easy to modulate,
provided you're not inebriated and have practiced a few panic stops,
and shouldn't necessitate the purchase of a new bicycle.

Be careful when posting questions like this, because you may attract
'bent riders, who are bearded hammers in search of nails--sometimes
with orange flippy flags!

[TBerk]

On Apr 30, 9:48 pm, wrote:
> The Berk wrote:
> > Obviously I would assume they could if you clamp down fast enough.
> > I ask because I bruised some rib bones this week when I stomped the
> > front brake and *surprise* I found out later my front rim has a
> > bubble bend in it from (I guess) a pot hole at some recent time.
> > Made for a portion of the rim that just wasn't going to get past the
> > brake pads, not while I was trying to actually use said brakes.
> > It would seem a better setup would be one unaffected by a slightly
> > bent rim, or so I wonder.
>
> http://www.sheldonbrown.com/brandt/over-the-bars.html
>
> > it would have been funny if it hadn't hurt so much at the time
>
> Don't laugh. I wouldn't be so ready to tell all that I used bicycle
> brakes in such a clumsy manner. Skilled motorcyclists do nose-down
> wheelies at high speed, often crossing the finish line on only the
> front wheel. That takes a bit of extra skill. A motorcyclist crashed
> fatally yesterday in East Palo Alto doing that.
>
> Jobst Brandt


Bite me Jobst.

TBerk

[TBerk]

On May 1, 6:47 am, landotter > wrote:
> On Apr 30, 10:49 pm, TBerk > wrote:
>
> > Obviously I would assume they could if you clamp down fast enough.
>
> Yes, if you don't brace yourself and are unfamiliar with the brake and
> grab wildly, any powerful brake can be dangerous--but so can many
> things in life. Well adjusted brakes should be easy to modulate,
> provided you're not inebriated and have practiced a few panic stops,
> and shouldn't necessitate the purchase of a new bicycle.
>
> Be careful when posting questions like this, because you may attract
> 'bent riders, who are bearded hammers in search of nails--sometimes
> with orange flippy flags!



Yeah, I have a feeling a got one of them on the line right now.

Folks, obviously if I had known the rim had a problem I would have
factored that in, either readjusting the brakes, massaging the rim,
drove around instead of stopping suddenly,and/or all of the above.

TBerk

[[email protected]]

Doug Cimper wrote:

>>> Obviously I would assume they could if you clamp down fast enough.

>>> I ask because I bruised some rib bones this week when I stomped the
>>> front brake and *surprise* I found out later my front rim has a
>>> bubble bend in it from (I guess) a pot hole at some recent time.
>>> ....

http://www.sheldonbrown.com/brandt/over-the-bars.html

>>> it would have been funny if it hadn't hurt so much at the time

>> Don't laugh. I wouldn't be so ready to tell all that I used
>> bicycle brakes in such a clumsy manner. Skilled motorcyclists do
>> nose-down wheelies at high speed, often crossing the finish line on
>> only the front wheel. That takes a bit of extra skill. A
>> motorcyclist crashed fatally yesterday in East Palo Alto doing
>> that.

> As someone else noted, most recumbents are immune to this
> flipping-over-forward problem under hard braking. In my opinion
> this is another reason that recumbents may be safer for general
> use--in that during a panic stop, the brakes can be applied with
> wild abandon and while the bike may slide out and drop the rider
> sideways, at least it's not going to flip them over onto their
> head...

I think you should read the FAQ item first at:

http://www.sheldonbrown.com/brandt/over-the-bars.html

before giving the usual endless pitch about the superiority of
recumbents. Going over the bars, especially with disk brakes, is
highly unlikely to be caused by locking the front wheel, but rather
follows the scenario described in the FAQ.

Jobst Brandt

[Jay Beattie]

On May 1, 6:47*am, landotter > wrote:
> On Apr 30, 10:49 pm, TBerk > wrote:
>
> > Obviously I would assume they could if you clamp down fast enough.
>
> Yes, if you don't brace yourself and are unfamiliar with the brake and
> grab wildly, any powerful brake can be dangerous--but so can many
> things in life. Well adjusted brakes should be easy to modulate,
> provided you're not inebriated and have practiced a few panic stops,
> and shouldn't necessitate the purchase of a new bicycle.
>
> Be careful when posting questions like this, because you may attract
> 'bent riders, who are bearded hammers in search of nails--sometimes
> with orange flippy flags!

Oooooh. You're gonna get it now! Those recumbent guys are mean --
head for the hills. Really -- and don't wait at the top.

For the OP: Properly adjusted mechanical discs are no more likely to
put you over the bars than properly adjusted dual-pivots with good
pads and straight rims. They have a different feel and they perform
far better in wet weather, but they are not scary strong -- at least
not the ones on my cross/commuter bike. Discs oviously are immune to
rim problems, but they have their own set of potential problems
including wharped rotors, bent pad clips, etc., etc. Like everyone
said, any good brake can launch you in a panic stop if you are not
properly positioned. -- Jay Beattie.

[[email protected]]

The Berk wrote:

>>> Obviously I would assume they could if you clamp down fast enough.

>> Yes, if you don't brace yourself and are unfamiliar with the brake and
>> grab wildly, any powerful brake can be dangerous--but so can many
>> things in life. Well adjusted brakes should be easy to modulate,
>> provided you're not inebriated and have practiced a few panic stops,
>> and shouldn't necessitate the purchase of a new bicycle.

>> Be careful when posting questions like this, because you may attract
>> 'bent riders, who are bearded hammers in search of nails--sometimes
>> with orange flippy flags!

> Yeah, I have a feeling a got one of them on the line right now.

> Folks, obviously if I had known the rim had a problem I would have
> factored that in, either readjusting the brakes, massaging the rim,
> drove around instead of stopping suddenly,and/or all of the above.

Wait a minute. You started this thread with the heading about "disk
brakes". How about getting the description consistent with the story.
Besides, unless a rim is offset so there is a significant step in the
alignment before and after a break, a ding in a rim will also not
cause the front wheel to lock.

You "went over the bars" in the usual manner and leave it at that.

Jobst Brandt

[[email protected]]

On May 1, 11:39 am, TBerk > wrote:
>
>
> Folks, obviously if I had known the rim had a problem I would have
> factored that in, either readjusting the brakes, massaging the rim,
> drove around instead of stopping suddenly,and/or all of the above.

I'm surprised this happened to you, for several reasons.

One is, a minor ding in a rim should be noticeable the first time you
gently touch the brakes, maybe even sooner. If that happened,
wouldn't you know not to jam the brakes on hard?

A second is, hard braking should be a very rare occurrence, unless
perhaps you ride down lots of truly extreme hills. If there were room
to ride around whatever it was, wouldn't you do that instead of panic
braking?

I suppose it's possible that you had a really major ding in the rim,
and it occurred immediately before you hit the brakes, so your first
brake application was the one that threw you. But that seems
unlikely.

BTW, I don't think that readjusting the brakes would help. No matter
how much rim clearance they have when released, they're going to have
zero rim clearance when you apply them.

Disk brakes have their own problems. Rather than contemplating a
switch, I think it's better to learn to care for your bike, and pay
attention to the road. And I'm not trying to sound harsh. That's
just the way it is.

- Frank Krygowski

[Michael Press]

In article
>,
TBerk > wrote:

> On Apr 30, 9:48 pm, wrote:
> > The Berk wrote:
> > > Obviously I would assume they could if you clamp down fast enough.
> > > I ask because I bruised some rib bones this week when I stomped the
> > > front brake and *surprise* I found out later my front rim has a
> > > bubble bend in it from (I guess) a pot hole at some recent time.
> > > Made for a portion of the rim that just wasn't going to get past the
> > > brake pads, not while I was trying to actually use said brakes.
> > > It would seem a better setup would be one unaffected by a slightly
> > > bent rim, or so I wonder.
> >
> > http://www.sheldonbrown.com/brandt/over-the-bars.html
> >
> > > it would have been funny if it hadn't hurt so much at the time
> >
> > Don't laugh. I wouldn't be so ready to tell all that I used bicycle
> > brakes in such a clumsy manner. Skilled motorcyclists do nose-down
> > wheelies at high speed, often crossing the finish line on only the
> > front wheel. That takes a bit of extra skill. A motorcyclist crashed
> > fatally yesterday in East Palo Alto doing that.
> >
> > Jobst Brandt
>
>
> Bite me Jobst.
>

TBerk, have you ever gone over your bars while braking?

--
Michael Press

[Michael Press]

In article >,
Michael Press > wrote:

> In article
> >,
> TBerk > wrote:
>
> > On Apr 30, 9:48 pm, wrote:
> > > The Berk wrote:
> > > > Obviously I would assume they could if you clamp down fast enough.
> > > > I ask because I bruised some rib bones this week when I stomped the
> > > > front brake and *surprise* I found out later my front rim has a
> > > > bubble bend in it from (I guess) a pot hole at some recent time.
> > > > Made for a portion of the rim that just wasn't going to get past the
> > > > brake pads, not while I was trying to actually use said brakes.
> > > > It would seem a better setup would be one unaffected by a slightly
> > > > bent rim, or so I wonder.
> > >
> > > http://www.sheldonbrown.com/brandt/over-the-bars.html
> > >
> > > > it would have been funny if it hadn't hurt so much at the time
> > >
> > > Don't laugh. I wouldn't be so ready to tell all that I used bicycle
> > > brakes in such a clumsy manner. Skilled motorcyclists do nose-down
> > > wheelies at high speed, often crossing the finish line on only the
> > > front wheel. That takes a bit of extra skill. A motorcyclist crashed
> > > fatally yesterday in East Palo Alto doing that.

[...]
TBerk, sorry. I was not paying attention,
and did not see you are the original poster.

--
Michael Press

[DougC]

wrote:
>
> I think you should read the FAQ item first at:
>
> http://www.sheldonbrown.com/brandt/over-the-bars.html
>
> before giving the usual endless pitch about the superiority of
> recumbents. Going over the bars, especially with disk brakes, is
> highly unlikely to be caused by locking the front wheel, but rather
> follows the scenario described in the FAQ.
>

The problem with the concept of "bracing with the arms" to use the front
brake of an upright bicycle is that--by nature--most crashes are
basically unanticipated. That's why there's crashes.

And as I noted--a bicycle doesn't need to tip completely over forward to
be unsafe during a panic stop. Merely un-weighting the rear tire enough
for the rear end to swing out left or right can result in a crash.

This is easy to demonstrate on pretty much any upright bicycle with
decent front brakes, and just about impossible to do on any
long-wheelbase recumbent. If one is worried about "going over the bars"
during a panic stop, it *IS* possible to pick a bicycle that basically
won't ever do it.
~

[Ron Ruff]

On May 1, 2:33*am, " >
wrote:
> Disk brakes have more stopping power and any such 'stomp' can result
> in a flip, not requiring any irregularities. *Due to their design,
> recumbents are immune from such a flip.

Even regular road brakes are strong enough to do this.

[landotter]

On May 1, 10:49 am, Jay Beattie > wrote:
> On May 1, 6:47 am, landotter > wrote:
>
> > On Apr 30, 10:49 pm, TBerk > wrote:
>
> > > Obviously I would assume they could if you clamp down fast enough.
>
> > Yes, if you don't brace yourself and are unfamiliar with the brake and
> > grab wildly, any powerful brake can be dangerous--but so can many
> > things in life. Well adjusted brakes should be easy to modulate,
> > provided you're not inebriated and have practiced a few panic stops,
> > and shouldn't necessitate the purchase of a new bicycle.
>
> > Be careful when posting questions like this, because you may attract
> > 'bent riders, who are bearded hammers in search of nails--sometimes
> > with orange flippy flags!
>
> Oooooh. You're gonna get it now! Those recumbent guys are mean --
> head for the hills. Really -- and don't wait at the top.

/me waits for Tom Sherman to show up in his aero spandex Nurse Ratchet
uniform.

[DougC]

TBerk wrote:
>
> Yeah, I have a feeling a got one of them on the line right now.
>
>
> TBerk

The difference is between someone telling you it's your fault and to fix
the bike and keep riding,

and someone else telling you there's another kind of bike that this sort
of thing /never/ happens on, and that you can't even /make/ it happen if
you /try/.

------

Recumbents aren't better at all things but they have significant
advantages in several aspects, and emergency braking tends to be one of
them.
~

[JG]

> Disk brakes have more stopping power and ...

No they don't. Every unassisted brake system has the energy from your
two hands to work with to drive rubber pads into the rotor or rim.
You can make this more or less efficient, but you can't change this
fundamental limitation.

JG

[landotter]

On May 1, 12:51 pm, Harry Brogan
<hbrogan57_AT_NOSPAM_DOT_YAHOO_DOT_COM> wrote:
> On Thu, 1 May 2008 06:47:38 -0700 (PDT), landotter
>
> > wrote:
> >On Apr 30, 10:49 pm, TBerk > wrote:
> >> Obviously I would assume they could if you clamp down fast enough.
>
> >Yes, if you don't brace yourself and are unfamiliar with the brake and
> >grab wildly, any powerful brake can be dangerous--but so can many
> >things in life. Well adjusted brakes should be easy to modulate,
> >provided you're not inebriated and have practiced a few panic stops,
> >and shouldn't necessitate the purchase of a new bicycle.
>
> >Be careful when posting questions like this, because you may attract
> >'bent riders, who are bearded hammers in search of nails--sometimes
> >with orange flippy flags!
>
> I do NOT have orange flippy flags!

Yellow?

[A Muzi]

>> TBerk > wrote:
>>> Obviously I would assume they could if you clamp down fast enough.

> landotter > wrote:
>> Yes, if you don't brace yourself and are unfamiliar with the brake and
>> grab wildly, any powerful brake can be dangerous--but so can many
>> things in life. Well adjusted brakes should be easy to modulate,
>> provided you're not inebriated and have practiced a few panic stops,
>> and shouldn't necessitate the purchase of a new bicycle.
>> Be careful when posting questions like this, because you may attract
>> 'bent riders, who are bearded hammers in search of nails--sometimes
>> with orange flippy flags!

Harry Brogan wrote:
> I do NOT have orange flippy flags!!!!!! ROFLMAO

Not yet?
Tom Sherman can probably help you choose a nice flippy orange one.
--
Andrew Muzi
<www.yellowjersey.org/>
Open every day since 1 April, 1971
** Posted from http://www.teranews.com **

[Ben C]

On 2008-05-01, JG > wrote:
>> Disk brakes have more stopping power and ...
>
> No they don't. Every unassisted brake system has the energy from your
> two hands to work with to drive rubber pads into the rotor or rim.
> You can make this more or less efficient, but you can't change this
> fundamental limitation.

You sort of can, with leverage.

It's not really the energy from your hands that's important, but the
force they can apply. That force can be geared up to give you as much
force as you want on the rim/disk.

You need four times as much force on a disk because it has about a
quarter the radius of the wheel. But in either case you just gear it so
it feels right for people with averagely normal hand strength. This
isn't the difficult part of brake design.

Lots of cars didn't used to have servo assistance on the brakes. All the
force and work required to brake came from your leg. And yet you could
slow down a tonne of car from 70mph like that.

The difficult part is getting rid of all the heat that the brakes are
converting the bike's kinetic energy into.

Bicycle rims have enough heat capacity to just soak up the heat for most
stopping situations, but they can overheat badly if you need to keep
them on continuously because you want to go down a hill quite slowly.

Disks have less capacity, but get hotter, so dissipate heat to the air
more rapidly. So I reckon they're better for sustainable braking down
long hills.

But for emergency stops either kind of brake (of decent quality and
level of maintenance) will be able to tip you over the handlebars if you
aren't careful.

[[email protected]]

Ben C? wrote:

>>> Disk brakes have more stopping power and...

>> No they don't. Every unassisted brake system has the energy from
>> your two hands to work with to drive rubber pads into the rotor or
>> rim. You can make this more or less efficient, but you can't
>> change this fundamental limitation.

> You sort of can, with leverage.

As is apparent, leverage cannot be arbitrarily changed without other
effects that require difficult redesign. Dual pivot rim brake
calipers are a classic example. To achieve the higher MA required by
today's riders pad clearance had to be reduced and this required
forced centering to prevent brake drag. Disks have the same problem.

> It's not really the energy from your hands that's important, but the
> force they can apply. That force can be geared up to give you as
> much force as you want on the rim/disk.

In what units are you measuring "energy" or do you mean "force"?

> You need four times as much force on a disk because it has about a
> quarter the radius of the wheel. But in either case you just gear it
> so it feels right for people with averagely normal hand
> strength. This isn't the difficult part of brake design.

That isn't the parameter of interest. Disk diameter and coefficient
of friction both have a major effect on the ratio between application
force and brake torque.

> Lots of cars didn't used to have servo assistance on the brakes.
> All the force and work required to brake came from your leg. And
> yet you could slow down a tonne of car from 70mph like that.

Drum brakes used massive self servo action to achieve useful braking.
Because that effect is highly unpredictable, they had both lock-up and
fade. That is why we use disks today. You may recall that this was
discussed here at great length.

> The difficult part is getting rid of all the heat that the brakes
> are converting the bike's kinetic energy into.

Apparently the bicycle industry is not addressing that part of the
problem when the surface area and thermal mass their gossamer rings of
steel have. I have asked brake manufacturers why their disks are
mostly air with a thin pattern of thin steel between. For cooling is
the answer. Maybe they should tell the automotive and railway people
about their theory.

> Bicycle rims have enough heat capacity to just soak up the heat for
> most stopping situations, but they can overheat badly if you need to
> keep them on continuously because you want to go down a hill quite
> slowly.

It depends on gradient that gives (vertical) foot (rider weight
(pounds) per second. The slower you go the less cooling and the less
wind drag on the rider. There is a narrow trade-off between brake
cooling and speed which was discussed here recently.

> Disks have less capacity, but get hotter, so dissipate heat to the
> air more rapidly. So I reckon they're better for sustainable
> braking down long hills.

By that measure, a wafer thin disk is all it takes, surface area and
mass be damned.

> But for emergency stops either kind of brake (of decent quality and
> level of maintenance) will be able to tip you over the handlebars if
> you aren't careful.

I doubt it. I don't know many riders who can raise the rear wheel
while traveling at normal road speeds. In contrast, I have seen
people go over the bars:

http://tinyurl.com/3kunfl

Jobst Brandt

[_[_2_]]

On Thu, 01 May 2008 12:02:27 -0500, DougC wrote:

> wrote:
>>
>> I think you should read the FAQ item first at:
>>
>> http://www.sheldonbrown.com/brandt/over-the-bars.html
>>
>> before giving the usual endless pitch about the superiority of
>> recumbents. Going over the bars, especially with disk brakes, is
>> highly unlikely to be caused by locking the front wheel, but rather
>> follows the scenario described in the FAQ.
>>
>
> The problem with the concept of "bracing with the arms" to use the front
> brake of an upright bicycle is that--by nature--most crashes are
> basically unanticipated. That's why there's crashes.
>
> And as I noted--a bicycle doesn't need to tip completely over forward to
> be unsafe during a panic stop. Merely un-weighting the rear tire enough
> for the rear end to swing out left or right can result in a crash.
>

Or, like the Raptor trike, be badly designed - that one had a very small
bolt loaded in shear about 1" from the front wheel axle as a means of
controlling brake torque. It broke when the ten-year old was riding it;
the steering arm went forward pulling him over the front wheels and out of
the trike; fortunately he was on the pavement at the time.

It's been fixed now; the brake torque is now taken by a triangluted
arrangement that is much larger and much stronger, with only a few ounces
additional weight.

[landotter]

On May 1, 6:47 pm, Harry Brogan
<hbrogan57_AT_NOSPAM_DOT_YAHOO_DOT_COM> wrote:
> On Thu, 1 May 2008 11:21:35 -0700 (PDT), landotter
>
>
>
> > wrote:
> >On May 1, 12:51 pm, Harry Brogan
> ><hbrogan57_AT_NOSPAM_DOT_YAHOO_DOT_COM> wrote:
> >> On Thu, 1 May 2008 06:47:38 -0700 (PDT), landotter
>
> >> > wrote:
> >> >On Apr 30, 10:49 pm, TBerk > wrote:
> >> >> Obviously I would assume they could if you clamp down fast enough.
>
> >> >Yes, if you don't brace yourself and are unfamiliar with the brake and
> >> >grab wildly, any powerful brake can be dangerous--but so can many
> >> >things in life. Well adjusted brakes should be easy to modulate,
> >> >provided you're not inebriated and have practiced a few panic stops,
> >> >and shouldn't necessitate the purchase of a new bicycle.
>
> >> >Be careful when posting questions like this, because you may attract
> >> >'bent riders, who are bearded hammers in search of nails--sometimes
> >> >with orange flippy flags!
>
> >> I do NOT have orange flippy flags!
>
> >Yellow?
>
> FUNNY!!!!......No....not yellow either.....Here's a photo....
>
> http://i255.photobucket.com/albums/hh160/1957trike/The%20Rig/1000Mile...

You could accent Old Glory with an international Pantheon of flippy
flags! Might affect your aerodynamics.

[clare at snyder dot ontario dot canada]

On Thu, 1 May 2008 01:33:03 -0700 (PDT), "
> wrote:

>On Apr 30, 10:49 pm, TBerk > wrote:
>> Obviously I would assume they could if you clamp down fast enough.
>>
>> I ask because I bruised some rib bones this week when I stomped the
>> front brake and *surprise* I found out later my front rim has a bubble
>> bend in it from (I guess) a pot hole at some recent time.
>>
>> Made for a portion of the rim that just wasn't going to get past the
>> brake pads, not while I was trying to actually use said brakes.
>>
>> It would seem a better setup would be one unaffected by a slightly
>> bent rim, or so I wonder.
>>
>> TBerk
>> it would have been funny if it hadn't hurt so much at the time
>
>Disk brakes have more stopping power and any such 'stomp' can result
>in a flip, not requiring any irregularities. Due to their design,
>recumbents are immune from such a flip.


Even the relatively ineffectual old "atom" drum brake could "unhorse"
you under the right circumstances.
** Posted from http://www.teranews.com **

[Tom Sherman[_2_]]

aka Mike Schwab wrote:
> On Apr 30, 10:49 pm, TBerk > wrote:
>> Obviously I would assume they could if you clamp down fast enough.
>>
>> I ask because I bruised some rib bones this week when I stomped the
>> front brake and *surprise* I found out later my front rim has a bubble
>> bend in it from (I guess) a pot hole at some recent time.
>>
>> Made for a portion of the rim that just wasn't going to get past the
>> brake pads, not while I was trying to actually use said brakes.
>>
>> It would seem a better setup would be one unaffected by a slightly
>> bent rim, or so I wonder.
>>
>> TBerk
>> it would have been funny if it hadn't hurt so much at the time
>
> Disk brakes have more stopping power and any such 'stomp' can result
> in a flip, not requiring any irregularities. Due to their design,
> recumbents are immune from such a flip.

Recumbents with PROPER weight distribution will skid the front wheel
instead of sending the rider over the bars. Some early bad designs, such
as the Hypercycle, would send the rider off the front under heavy
braking, and had too little weight on the rear wheel for it to provide
much braking.

I often wonder if the Hypercycle and its ilk are responsible for much of
the negative attitudes towards recumbents by certain riders. Certainly,
if a rider's only experience was the ill handling, poor climbing and
poor braking Hypercycle, they would not look kindly on recumbents as a
whole.

--
Tom Sherman - Holstein-Friesland Bovinia
The weather is here, wish you were beautiful

[TBerk]

On May 1, 9:25 am, Michael Press > wrote:
> In article >,
> Michael Press > wrote:
>
>
>
> > In article
> > >,
> > TBerk > wrote:
>
> > > On Apr 30, 9:48 pm, wrote:
> > > > The Berk wrote:
> > > > > Obviously I would assume they could if you clamp down fast enough.
> > > > > I ask because I bruised some rib bones this week when I stomped the
> > > > > front brake and *surprise* I found out later my front rim has a
> > > > > bubble bend in it from (I guess) a pot hole at some recent time.
> > > > > Made for a portion of the rim that just wasn't going to get past the
> > > > > brake pads, not while I was trying to actually use said brakes.
> > > > > It would seem a better setup would be one unaffected by a slightly
> > > > > bent rim, or so I wonder.
>
> > > > http://www.sheldonbrown.com/brandt/over-the-bars.html
>
> > > > > it would have been funny if it hadn't hurt so much at the time
>
> > > > Don't laugh. I wouldn't be so ready to tell all that I used bicycle
> > > > brakes in such a clumsy manner. Skilled motorcyclists do nose-down
> > > > wheelies at high speed, often crossing the finish line on only the
> > > > front wheel. That takes a bit of extra skill. A motorcyclist crashed
> > > > fatally yesterday in East Palo Alto doing that.
>
> [...]
> TBerk, sorry. I was not paying attention,
> and did not see you are the original poster.
>
> --
> Michael Press

Not a problem, in fact I am able to modulate the front brake, even in
panic stops just fine.

What got me this time was a deformation of the front wheel; one that
didn't show as a side to side wobble where I would have noticed it out
of the corner of my eye but a symetrical dent on both walls.

Brakes stopped 'real quick like' despite not otherwise being locked
up.


TBerk

[TBerk]

On May 1, 8:58 am, wrote:
> The Berk wrote:
> >>> Obviously I would assume they could if you clamp down fast enough.
> >> Yes, if you don't brace yourself and are unfamiliar with the brake and
> >> grab wildly, any powerful brake can be dangerous--but so can many
> >> things in life. Well adjusted brakes should be easy to modulate,
> >> provided you're not inebriated and have practiced a few panic stops,
> >> and shouldn't necessitate the purchase of a new bicycle.
> >> Be careful when posting questions like this, because you may attract
> >> 'bent riders, who are bearded hammers in search of nails--sometimes
> >> with orange flippy flags!
> > Yeah, I have a feeling a got one of them on the line right now.
> > Folks, obviously if I had known the rim had a problem I would have
> > factored that in, either readjusting the brakes, massaging the rim,
> > drove around instead of stopping suddenly,and/or all of the above.
>
> Wait a minute. You started this thread with the heading about "disk
> brakes". How about getting the description consistent with the story.
> Besides, unless a rim is offset so there is a significant step in the
> alignment before and after a break, a ding in a rim will also not
> cause the front wheel to lock.
>
> You "went over the bars" in the usual manner and leave it at that.
>
> Jobst Brandt

You are no longer invited to bite me, in this case Big Green Donkeys
are your answer.

1) I am well aware of my conventional, on the rim, brakes.

2) I had a deformation of the rim that caused them to lock during a
sudden, but seemingly manageable stopping maneuver.

3) There is a question I posted to the newsgroup about alternative
brake systems; disk brakes.

There comes along a knucklehead who is confused about my posting but
seems to have figured out the mysteries of life... only I am not
paying him any mind.

Thanks most everybody else.


TBerk

[TBerk]

On May 1, 9:15 am, wrote:
<snip>
> BTW, I don't think that readjusting the brakes would help. No matter
> how much rim clearance they have when released, they're going to have
> zero rim clearance when you apply them.
>
> Disk brakes have their own problems. Rather than contemplating a
> switch, I think it's better to learn to care for your bike, and pay
> attention to the road. And I'm not trying to sound harsh. That's
> just the way it is.
>
> - Frank Krygowski

Good points.

The rim will need mending, no doubt. I might have adjusted the brakes
on the road to lessen the braking power. Just an option.

I contemplate a switch because my used frame has been in trouble for
awhile with some bent front forks. Replacing them pens up the option
of a disk brake capible setup.

No need to worry about sounding harsh, you veterans here don't know me
from Adam.

TBerk

[[email protected]]

Tom Sherman wrote:


>>> Obviously I would assume they could if you clamp down fast enough.

>>> I ask because I bruised some rib bones this week when I stomped
>>> the front brake and *surprise* I found out later my front rim has
>>> a bubble bend in it from (I guess) a pot hole at some recent time.

>>> Made for a portion of the rim that just wasn't going to get past
>>> the brake pads, not while I was trying to actually use said
>>> brakes.

>>> It would seem a better setup would be one unaffected by a slightly
>>> bent rim, or so I wonder.

>>> it would have been funny if it hadn't hurt so much at the time

>> Disk brakes have more stopping power and any such 'stomp' can
>> result in a flip, not requiring any irregularities. Due to their
>> design, recumbents are immune from such a flip.

> Recumbents with PROPER weight distribution will skid the front wheel
> instead of sending the rider over the bars. Some early bad designs,
> such as the Hypercycle, would send the rider off the front under
> heavy braking, and had too little weight on the rear wheel for it to
> provide much braking.

I've seen nay recumbents with a small front wheel and cranks and
pedals forward of that wheel. These units will endo easily while the
rider remains firmly in the seat. The advantage is that the rider, if
a bit agile, will land on his feet running. The bike does not fare as
well as it overturns and scraped the road.

> I often wonder if the Hypercycle and its ilk are responsible for
> much of the negative attitudes toward recumbents by certain
> riders. Certainly, if a rider's only experience was the ill
> handling, poor climbing and poor braking Hypercycle, they would not
> look kindly on recumbents as a whole.

Long wheelbase recumbents have a slew of other problems in
maneuverability and climbing rough stuff. Disk brakes are not one of
their problems.

Jobst Brandt

[Tom Sherman[_2_]]

aka Jobst Brandt wrote:
> Tom Sherman wrote:
>
>
>>>> Obviously I would assume they could if you clamp down fast enough.
>
>>>> I ask because I bruised some rib bones this week when I stomped
>>>> the front brake and *surprise* I found out later my front rim has
>>>> a bubble bend in it from (I guess) a pot hole at some recent time.
>
>>>> Made for a portion of the rim that just wasn't going to get past
>>>> the brake pads, not while I was trying to actually use said
>>>> brakes.
>
>>>> It would seem a better setup would be one unaffected by a slightly
>>>> bent rim, or so I wonder.
>
>>>> it would have been funny if it hadn't hurt so much at the time
>
>>> Disk brakes have more stopping power and any such 'stomp' can
>>> result in a flip, not requiring any irregularities. Due to their
>>> design, recumbents are immune from such a flip.
>
>> Recumbents with PROPER weight distribution will skid the front wheel
>> instead of sending the rider over the bars. Some early bad designs,
>> such as the Hypercycle, would send the rider off the front under
>> heavy braking, and had too little weight on the rear wheel for it to
>> provide much braking.
>
> I've seen nay recumbents with a small front wheel and cranks and
> pedals forward of that wheel. These units will endo easily while the
> rider remains firmly in the seat.

Absolutely NOT true in my experience of short-wheelbase recumbent
bicycles with proper weight distribution (e.g. RANS Rocket, RANS V-Rex,
RANS Vivo, Lighting P-38, Burley HepCat, Reynolds Wishbone, and of
course the Earth Cycles Sunset).

On my Dragonflyer trike which has the crank ahead of the front wheels, I
can skid both on dry pavement without the rear wheel lifting.

How many modern short-wheelbase recumbent bicycles has Jobst Brandt
ridden to determine that "endos" are likely?

> The advantage is that the rider, if
> a bit agile, will land on his feet running. The bike does not fare as
> well as it overturns and scraped the road.
>
Mr. Brandt must be thinking of the Hypercycle or some other obsolete design.

>> I often wonder if the Hypercycle and its ilk are responsible for
>> much of the negative attitudes toward recumbents by certain
>> riders. Certainly, if a rider's only experience was the ill
>> handling, poor climbing and poor braking Hypercycle, they would not
>> look kindly on recumbents as a whole.
>
> Long wheelbase recumbents have a slew of other problems in
> maneuverability and climbing rough stuff. Disk brakes are not one of
> their problems.
>
Actually, front braking is more of a problem on a long-wheelbase
recumbent than a short-wheelbase recumbent, since it is much easier to
accidentally lock up the front wheel.

--
Tom Sherman - Holstein-Friesland Bovinia
The weather is here, wish you were beautiful

[Tom Sherman[_2_]]

Doug Cimper wrote:
> wrote:
>>
>> I think you should read the FAQ item first at:
>>
>> http://www.sheldonbrown.com/brandt/over-the-bars.html
>>
>> before giving the usual endless pitch about the superiority of
>> recumbents. Going over the bars, especially with disk brakes, is
>> highly unlikely to be caused by locking the front wheel, but rather
>> follows the scenario described in the FAQ.
>>
>
> The problem with the concept of "bracing with the arms" to use the front
> brake of an upright bicycle is that--by nature--most crashes are
> basically unanticipated. That's why there's crashes.
> [...]

On a recumbent bicycle, the rider does not need to brace with his/her
arms to keep from going over the bars, as his/her legs are naturally in
a position to provide the required bracing.

The above would be obvious to someone who has actually ridden a properly
designed recumbent in real world settings.

--
Tom Sherman - Holstein-Friesland Bovinia
The weather is here, wish you were beautiful

[Tom Sherman[_2_]]

landotter wrote:
> On Apr 30, 10:49 pm, TBerk > wrote:
>> Obviously I would assume they could if you clamp down fast enough.
>
> Yes, if you don't brace yourself and are unfamiliar with the brake and
> grab wildly, any powerful brake can be dangerous--but so can many
> things in life. Well adjusted brakes should be easy to modulate,
> provided you're not inebriated and have practiced a few panic stops,
> and shouldn't necessitate the purchase of a new bicycle.
>
> Be careful when posting questions like this, because you may attract
> 'bent riders, who are bearded hammers in search of nails--sometimes
> with orange flippy flags!
>
Since so many upright riders feel necessary to comment on the alleged
disadvantages of recumbents (often quite rudely in person), it is only
fair to do the same for uprights.

--
Tom Sherman - Holstein-Friesland Bovinia
The weather is here, wish you were beautiful

[Tom Sherman[_2_]]

aka Jobst Brandt wrote:
> Ben C? wrote:
> [...]
>> But for emergency stops either kind of brake (of decent quality and
>> level of maintenance) will be able to tip you over the handlebars if
>> you aren't careful.
>
> I doubt it. I don't know many riders who can raise the rear wheel
> while traveling at normal road speeds. In contrast, I have seen
> people go over the bars:[...]

It is much easier to lift the rear wheel if the bicycle has a suspension
fork. I can do "stoppies" quite easily on my Trek 6000, even with the
knobby tread tires.

--
Tom Sherman - Holstein-Friesland Bovinia
The weather is here, wish you were beautiful

[TBerk]

On May 1, 8:31 pm, Tom Sherman >
wrote:
> landotter wrote:
<snippage>
> > Be careful when posting questions like this, because you may attract
> > 'bent riders, who are bearded hammers in search of nails--sometimes
> > with orange flippy flags!
>
> Since so many upright riders feel necessary to comment on the alleged
> disadvantages of recumbents (often quite rudely in person), it is only
> fair to do the same for uprights.
>
> --
> Tom Sherman -

But yeah, you guys are thread-jacking though.


TBerk

[Tom Sherman[_2_]]

TBerk ? wrote:
> On May 1, 8:31 pm, Tom Sherman >
> wrote:
>> landotter wrote:
> <snippage>
>>> Be careful when posting questions like this, because you may attract
>>> 'bent riders, who are bearded hammers in search of nails--sometimes
>>> with orange flippy flags!
>> Since so many upright riders feel necessary to comment on the alleged
>> disadvantages of recumbents (often quite rudely in person), it is only
>> fair to do the same for uprights.
>>
>> --
>> Tom Sherman -
>
> But yeah, you guys are thread-jacking though.
>
In other breaking news...

Thread drift is a fact of life on Usenet.

--
Tom Sherman - Holstein-Friesland Bovinia
The weather is here, wish you were beautiful

[Zebee Johnstone]

In alt.rec.bicycles.recumbent on Thu, 01 May 2008 22:28:25 -0500
Tom Sherman > wrote:
>
> On a recumbent bicycle, the rider does not need to brace with his/her
> arms to keep from going over the bars, as his/her legs are naturally in
> a position to provide the required bracing.

And on a recumbent with a hinged stem (such as my Bacchetta Giro)
bracing with the hands is a Bad Idea!

(as I found out on the test ride.....)

Zebee

[Peter Clinch]

wrote:

> I've seen nay recumbents with a small front wheel and cranks and
> pedals forward of that wheel.

My Streetmachine has a 20" front wheel and the cranks ahead of it.

> These units will endo easily while the
> rider remains firmly in the seat.

For some values of "easily"... I find that if I slam on the anchors in
an emergency stop I get both wheels skidding, and no hint of an endo.

> The advantage is that the rider, if
> a bit agile, will land on his feet running. The bike does not fare as
> well as it overturns and scraped the road.

What happens in my direct experience on a Streetmachine is I skid to a
stop, still in the seat, still the right way up and think "!"
For me, direct empirical evidence trumps theory.

Pete.
--
Peter Clinch Medical Physics IT Officer
Tel 44 1382 660111 ext. 33637 Univ. of Dundee, Ninewells Hospital
Fax 44 1382 640177 Dundee DD1 9SY Scotland UK
net http://www.dundee.ac.uk/~pjclinch/

[Ben C]

On 2008-05-01, > wrote:
[...]
>> It's not really the energy from your hands that's important, but the
>> force they can apply. That force can be geared up to give you as
>> much force as you want on the rim/disk.
>
> In what units are you measuring "energy" or do you mean "force"?

I'm not measuring energy but if I was I would use Joules.
I mean energy when I say "energy" and force when I say "force".

My point is that it takes very little energy from a rider to squeeze the
brakes. You have to move your fingers a short distance, but the main
requirement on your body is to maintain a force.

As discussed here previously continuous force maintenance by human
muscles does require the consumption of some energy, but it is only a
small amount.

>> You need four times as much force on a disk because it has about a
>> quarter the radius of the wheel. But in either case you just gear it
>> so it feels right for people with averagely normal hand
>> strength. This isn't the difficult part of brake design.
>
> That isn't the parameter of interest. Disk diameter and coefficient
> of friction both have a major effect on the ratio between application
> force and brake torque.

Yes that too, but the basic point is the same: you give the user enough
mechanical advantage to give the brakes a satisfactory feel whether they
are disk brakes or rim brakes.

An overgeared brake isn't a better brake.

>> Lots of cars didn't used to have servo assistance on the brakes.
>> All the force and work required to brake came from your leg. And
>> yet you could slow down a tonne of car from 70mph like that.
>
> Drum brakes used massive self servo action to achieve useful braking.
> Because that effect is highly unpredictable, they had both lock-up and
> fade. That is why we use disks today. You may recall that this was
> discussed here at great length.

There were plenty of cars with non-servo-assisted disks too.

>> The difficult part is getting rid of all the heat that the brakes
>> are converting the bike's kinetic energy into.
>
> Apparently the bicycle industry is not addressing that part of the
> problem when the surface area and thermal mass their gossamer rings of
> steel have.

This is why I think that disks don't really work as heat sinks but as
dissipators.

Here are my various guesses and estimates on which I'm basing this:
http://groups.google.co.uk/group/uk.rec.cycling/msg/991d32532f671264

> I have asked brake manufacturers why their disks are
> mostly air with a thin pattern of thin steel between. For cooling is
> the answer.

Ah but did they mean because they _look_ cool :)

> Maybe they should tell the automotive and railway people about their
> theory.

I remember a calculation here before about cross-drilled disks on cars.

I think your point was originally to slay a herring about "gas
bearings", which was fair enough, but I think it was concluded also that
a drilled disk will have a slightly higher surface area to volume ratio
than one that isn't drilled.

Same goes for a filigreed disk. But I don't really buy that "it cools
better" line either. It would have to be shown by how much and also what
the effect of a smaller surface area in contact with the pad has (for
car disks, I think those filigreed bike disks usually have a continuous
undrilled track that touches the pads).

>> Bicycle rims have enough heat capacity to just soak up the heat for
>> most stopping situations, but they can overheat badly if you need to
>> keep them on continuously because you want to go down a hill quite
>> slowly.
>
> It depends on gradient that gives (vertical) foot (rider weight
> (pounds) per second. The slower you go the less cooling and the less
> wind drag on the rider. There is a narrow trade-off between brake
> cooling and speed which was discussed here recently.

Indeed. For a given hill/bike there's a "worst speed" for heat buildup.
Descend either faster or slower than that speed and you're better off.

>> Disks have less capacity, but get hotter, so dissipate heat to the
>> air more rapidly. So I reckon they're better for sustainable
>> braking down long hills.
>
> By that measure, a wafer thin disk is all it takes, surface area and
> mass be damned.

Well surface area affects its dissipation rate, which does need to be
high by this measure.

But mass be damned, provided the thing's strong enough.

>> But for emergency stops either kind of brake (of decent quality and
>> level of maintenance) will be able to tip you over the handlebars if
>> you aren't careful.
>
> I doubt it. I don't know many riders who can raise the rear wheel
> while traveling at normal road speeds. In contrast, I have seen
> people go over the bars:
>
> http://tinyurl.com/3kunfl

Nice picture of a pedal, what's it got to do with going over the
handlebars?

I agree that it's hard to do though. I shouldn't have said "if you
aren't careful"-- it's not a problem practically speaking on any bike
I've ridden.

[Zebee Johnstone]

In alt.rec.bicycles.recumbent on 02 May 2008 01:44:09 GMT
> wrote:
> I've seen nay recumbents with a small front wheel and cranks and
> pedals forward of that wheel. These units will endo easily while the
> rider remains firmly in the seat. The advantage is that the rider, if
> a bit agile, will land on his feet running. The bike does not fare as
> well as it overturns and scraped the road.

Will they?

I've been hard on the picks (front disk even!) on my Giro 20 going
downhill. The back (v-brake) skidded, so I let up, I did my damndest not
to lock the front, and didn't (riding a motorcycle has some advantages)
but the thing showed no sign of an endo I could feel.

Indeed, trying same when I first got the disks didn't get me anywhere.
Locking the front is hard to do when you have trained for years not
to, so maybe I wasn't trying hard enough. Never felt a massive weight
transfer forward, nothing like pulling a stoppie on a motorcycle (which
I have done more than once).

If they will "endo easily" then I must be dreaming...

So I have to ask... have you ridden one? Have you managed to endo it?

If so, how? What did it feel like, when did the weight transfer get so
over rather than forward (hard transfer on a bent feels qualitatively
different to hard transfer on an upright to me), and how fast did you have
to go, and how fast were you going when you managed to get it to go over?


Zebee

[Tom Sherman[_2_]]

Zebee Johnstone wrote:
> In alt.rec.bicycles.recumbent on Thu, 01 May 2008 22:28:25 -0500
> Tom Sherman > wrote:
>> On a recumbent bicycle, the rider does not need to brace with his/her
>> arms to keep from going over the bars, as his/her legs are naturally in
>> a position to provide the required bracing.
>
> And on a recumbent with a hinged stem (such as my Bacchetta Giro)
> bracing with the hands is a Bad Idea!
>
> (as I found out on the test ride.....)
>
I have had to brake very hard when cut off by idiot cagers while
descending fast (70+ kph) on my RANS Rocket with a Flip-It® hinged
handlebar riser, and the bars did not move forward. And I can move the
bars forward and back with one little finger while at rest.

I have had the same experience on several other short-wheelbase
recumbents with hinged risers. Basically, freely hinged handlebars can
NOT restrain the rider from moving forward until they hit their forward
stop, which is farther than the rider can reach while seated. So the
legs and friction between the rider and the seat have to be providing
all the restraining force to keep the rider on the bike while braking.

--
Tom Sherman - Holstein-Friesland Bovinia
The weather is here, wish you were beautiful

[Tom Sherman[_2_]]

Zebee Johnstone wrote:
> In alt.rec.bicycles.recumbent on 02 May 2008 01:44:09 GMT
> > wrote:
>> I've seen nay recumbents with a small front wheel and cranks and
>> pedals forward of that wheel. These units will endo easily while the
>> rider remains firmly in the seat. The advantage is that the rider, if
>> a bit agile, will land on his feet running. The bike does not fare as
>> well as it overturns and scraped the road.
>
> Will they?
>
> I've been hard on the picks (front disk even!) on my Giro 20 going
> downhill. The back (v-brake) skidded, so I let up, I did my damndest not
> to lock the front, and didn't (riding a motorcycle has some advantages)
> but the thing showed no sign of an endo I could feel.
>
Since this is a Giro 20, it should be noted that the front wheel size is
ISO 406-mm, which is relevant, since the effectiveness of a disc (or
drum) brake increases with decreasing wheel diameter.

> Indeed, trying same when I first got the disks didn't get me anywhere.
> Locking the front is hard to do when you have trained for years not
> to, so maybe I wasn't trying hard enough. Never felt a massive weight
> transfer forward, nothing like pulling a stoppie on a motorcycle (which
> I have done more than once).
>
See other posts about the rider's legs providing bracing against the
rider moving forward.

> If they will "endo easily" then I must be dreaming...
>
> So I have to ask... have you ridden one? Have you managed to endo it?
>
The anti-recumbent "experts" don't need no steenkin' test rides!

> If so, how? What did it feel like, when did the weight transfer get so
> over rather than forward (hard transfer on a bent feels qualitatively
> different to hard transfer on an upright to me), and how fast did you have
> to go, and how fast were you going when you managed to get it to go over?
>
Back in the early days of the 20th Century recumbent revival (e.g.
Hypercycle, the never produced Avatar 1000,) the designers mistakenly
thought that some heel/wheel overlap needed to be avoided. Therefore,
the boom was made very long and the rider was seated almost over the
front wheel. This led to too flexible booms which made climbing and
acceleration poor, poor handling - especially when hitting bumps at
speed , and the bike rotating forward about the front wheel contact
patch under hard braking.

Modern short=wheelbase recumbent sensibly trade off some heel overlap
for proper weight distribution and have none of the above flaws.
However, some of the "experts" tried the earlier designs 25 or 30 years
ago and have closed their minds to later improvements.

--
Tom Sherman - Holstein-Friesland Bovinia
The weather is here, wish you were beautiful

[A Muzi]

>>> landotter wrote:
>>>> Be careful when posting questions like this, because you may attract
>>>> 'bent riders, who are bearded hammers in search of nails--sometimes
>>>> with orange flippy flags!

>> Tom Sherman > wrote:
>>> Since so many upright riders feel necessary to comment on the alleged
>>> disadvantages of recumbents (often quite rudely in person), it is only
>>> fair to do the same for uprights.

> TBerk ? wrote:
>> But yeah, you guys are thread-jacking though.

Tom Sherman wrote:
> In other breaking news...
> Thread drift is a fact of life on Usenet.

Sometimes more a feature than a problem!
--
Andrew Muzi
<www.yellowjersey.org/>
Open every day since 1 April, 1971
** Posted from http://www.teranews.com **

[Michael Press]

In article >,
Tom Sherman > wrote:

> TBerk ? wrote:
> > On May 1, 8:31 pm, Tom Sherman >
> > wrote:
> >> landotter wrote:
> > <snippage>
> >>> Be careful when posting questions like this, because you may attract
> >>> 'bent riders, who are bearded hammers in search of nails--sometimes
> >>> with orange flippy flags!
> >> Since so many upright riders feel necessary to comment on the alleged
> >> disadvantages of recumbents (often quite rudely in person), it is only
> >> fair to do the same for uprights.
> >
> > But yeah, you guys are thread-jacking though.
> >
> In other breaking news...
>
> Thread drift is a fact of life on Usenet.

Almost all non sequiturs on recumbent bicycles
are introduced by you. You walk, or roll supine,
with `Kick Me' sign and are surprised
that you are sore? Try going a year without
a gratuitous introduction of recumbent bicycles
and see how things work out.

>

--
Michael Press

[landotter]

On May 2, 12:17 am, Tom Sherman >
wrote:
> TBerk ? wrote:
> > On May 1, 8:31 pm, Tom Sherman >
> > wrote:
> >> landotter wrote:
> > <snippage>
> >>> Be careful when posting questions like this, because you may attract
> >>> 'bent riders, who are bearded hammers in search of nails--sometimes
> >>> with orange flippy flags!
> >> Since so many upright riders feel necessary to comment on the alleged
> >> disadvantages of recumbents (often quite rudely in person), it is only
> >> fair to do the same for uprights.
>
> >> --
> >> Tom Sherman -
>
> > But yeah, you guys are thread-jacking though.
>
> In other breaking news...
>
> Thread drift is a fact of life on Usenet.

Stick this in your humor section!

http://www.coldbacon.com/pics/kliban/bkhumor.gif

;o)

[N8N]

On May 1, 7:49*pm, wrote:
> Ben C? wrote:

<snip>

>
> > Lots of cars didn't used to have servo assistance on the brakes.
> > All the force and work required to brake came from your leg. *And
> > yet you could slow down a tonne of car from 70mph like that.
>
> Drum brakes used massive self servo action to achieve useful braking.
> Because that effect is highly unpredictable, they had both lock-up and
> fade. *That is why we use disks today. *You may recall that this was
> discussed here at great length.
>


I don't understand why you consider that action "highly unpredictable"
it's simply speed dependent. Sure they lock up if you stomp on 'em
but so will boosted discs. The fade comes from the inability of the
shoes and drum to shed heat as effectively as discs where all the
parts are out in the open and in some racing applications even have
forced air ducted over them for additional cooling. Old manual drum
brakes are actually quite pleasant to drive on, so long as you're not
racing or driving fast through the mountains. IMHO they have a much
better pedal feel than all but the best new disc brakes; certainly
more direct as there is a direct hydraulic connection between foot and
shoes with only a very few, simple mechanical parts in between.

> > The difficult part is getting rid of all the heat that the brakes
> > are converting the bike's kinetic energy into.
>
> Apparently the bicycle industry is not addressing that part of the
> problem when the surface area and thermal mass their gossamer rings of
> steel have. *I have asked brake manufacturers why their disks are
> mostly air with a thin pattern of thin steel between. *For cooling is
> the answer. *Maybe they should tell the automotive and railway people
> about their theory.

??? most automotive disc brakes are "vented," that is, the braking
surfaces are separated by a webbing of cast iron intended to have air
pass through. High-performance rotors are also cross-drilled and/or
slotted.

nate

[TBerk]

On May 1, 10:17 pm, Tom Sherman >
wrote:
> TBerk ? wrote:
<snip>
> >
> > But yeah, you guys are thread-jacking though.
>
> In other breaking news...
> Thread drift is a fact of life on Usenet.
>
> --
> Tom Sherman

Sorry, forgot to include an emoticon 8])


TBerk
I'm going to be looking into replacement forks with disk brake
capacity. Stay tuned everybody...

[[email protected]]

Nate Nagel wrote:

>>> Lots of cars didn't used to have servo assistance on the brakes.
>>> All the force and work required to brake came from your leg. Â*And
>>> yet you could slow down a tonne of car from 70mph like that.

>> Drum brakes used massive self servo action to achieve useful
>> braking. Because that effect is highly unpredictable, they had
>> both lock-up and fade. Â*That is why we use disks today. Â*You may
>> recall that this was discussed here at great length.

> I don't understand why you consider that action "highly unpredictable"
> it's simply speed dependent. Sure they lock up if you stomp on 'em
> but so will boosted discs. The fade comes from the inability of the
> shoes and drum to shed heat as effectively as discs where all the
> parts are out in the open and in some racing applications even have
> forced air ducted over them for additional cooling.

I think you don't know the history of the drum brake. It's self servo
action is laid out about a specific friction coefficient such that
when it is a bit high, brakes lock up (even after taking the foot off
the pedal) and when it is a bit low from heating, there is essentially
no brake at all, resulting in run-aways on mountain roads.

> Old manual drum brakes are actually quite pleasant to drive on, so
> long as you're not racing or driving fast through the mountains.
> IMHO they have a much better pedal feel than all but the best new
> disc brakes; certainly more direct as there is a direct hydraulic
> connection between foot and shoes with only a very few, simple
> mechanical parts in between.

Oh nostalgia for things that weren't. Read:

http://en.wikipedia.org/wiki/Brake_fade#Fade_in_drum_brakes

>>> The difficult part is getting rid of all the heat that the brakes
>>> are converting the bike's kinetic energy into.

That's why heavy trucks still use drum brakes, drums having large
surface to reject heat by forced convection. Highways have long dual
tired skid marks because the response to brake application cannot be
well controlled with drum brakes.

>> Apparently the bicycle industry is not addressing that part of the
>> problem when the surface area and thermal mass their gossamer rings of
>> steel have. Â*I have asked brake manufacturers why their disks are
>> mostly air with a thin pattern of thin steel between. Â*For cooling is
>> the answer. Â*Maybe they should tell the automotive and railway people
>> about their theory.

> ??? most automotive disc brakes are "vented," that is, the braking
> surfaces are separated by a webbing of cast iron intended to have air
> pass through. High-performance rotors are also cross-drilled and/or
> slotted.

I think you'll find that they are not vented but rather solid disks
with no holes. The cross drilling is found only on vehicles tauted to
be high performance while no passenger sedan has cross drilling that
has no technical advantage but is a relic of the days when brake fade
was believed to be caused by out-gassing of brake shoes to generate a
gas bearing. The holes allow that imaginary gas to escape.

I worked in brake design with Girling and ATE in the years when the
auto industry was changing to disks and was amazed at the amount of
myth and lore surrounding brakes.

Jobst Brandt

[Nate Nagel[_2_]]

wrote:
> Nate Nagel wrote:
>
>
>>>> Lots of cars didn't used to have servo assistance on the
>>>> brakes. All the force and work required to brake came from your
>>>> leg. And yet you could slow down a tonne of car from 70mph
>>>> like that.
>
>
>>> Drum brakes used massive self servo action to achieve useful
>>> braking. Because that effect is highly unpredictable, they had
>>> both lock-up and fade. That is why we use disks today. You may
>>> recall that this was discussed here at great length.
>
>
>> I don't understand why you consider that action "highly
>> unpredictable" it's simply speed dependent. Sure they lock up if
>> you stomp on 'em but so will boosted discs. The fade comes from
>> the inability of the shoes and drum to shed heat as effectively as
>> discs where all the parts are out in the open and in some racing
>> applications even have forced air ducted over them for additional
>> cooling.
>
>
> I think you don't know the history of the drum brake. It's self
> servo action is laid out about a specific friction coefficient such
> that when it is a bit high, brakes lock up (even after taking the
> foot off the pedal)

Which is not an issue on any automotive application, as if anything,
current non-asbestos linings have an even lower coefficient of friction
than the original linings around which the brake system was designed. I
have seen some high-performance linings made available for various
vintage drum brake setups (presumably for vintage racing) and have not
ever heard of this happening in practice.

> and when it is a bit low from heating, there is essentially no brake
> at all, resulting in run-aways on mountain roads.

That much is true. Of course this can also happen with discs, if you
abuse them enough, but discs cool down *much* faster than drums given
that the friction surface is in direct contact with cooling air, the
discs have a higher surface area to mass ratio, and that the calipers
and at least portions of the linings are also in closer proximity to
cooling air than in a drum brake.

>> Old manual drum brakes are actually quite pleasant to drive on, so
>> long as you're not racing or driving fast through the mountains.
>> IMHO they have a much better pedal feel than all but the best new
>> disc brakes; certainly more direct as there is a direct hydraulic
>> connection between foot and shoes with only a very few, simple
>> mechanical parts in between.
>
>
> Oh nostalgia for things that weren't. Read:
>
> http://en.wikipedia.org/wiki/Brake_fade#Fade_in_drum_brakes

Seeing as I actually own and (occasionally) drive a '55 Studebaker coupe
equipped with the (excellent) factory equipment brakes, with the only
upgrade being the addition of finned drums from a later model car, I can
say that they certainly aren't anywhere near the death-dealing devices
that you seem to be making them out to be. The three major shortcomings
of drum brakes in general are 1) brakes often undersized for the
vehicle, exacerbating other problems (not an issue on my car, but, say,
the 9" front drums on an old Dart are an insult to common sense.) 2)
Cooling - drum brakes do retain heat far more so than do discs,
resulting in earlier fading. 3) single circuit master cylinders can
result in complete brake system failure with one single hydraulic
failure. Not an issue with the drums themselves, but legal until the
late 60's and therefore common on most vehicles you'll find with four
wheel drum brakes.

>>>> The difficult part is getting rid of all the heat that the
>>>> brakes are converting the bike's kinetic energy into.
>
>
> That's why heavy trucks still use drum brakes, drums having large
> surface to reject heat by forced convection. Highways have long dual
> tired skid marks because the response to brake application cannot be
> well controlled with drum brakes.

I believe that they still use drums because they're easier to work with
in an air brake application. They still don't shed heat nearly as well
as to discs. I suspect many of those skid marks are also the result of
air system failures, not panic stops gone bad.

>>> Apparently the bicycle industry is not addressing that part of
>>> the problem when the surface area and thermal mass their gossamer
>>> rings of steel have. I have asked brake manufacturers why their
>>> disks are mostly air with a thin pattern of thin steel between.
>>> For cooling is the answer. Maybe they should tell the automotive
>>> and railway people about their theory.
>
>
>> ??? most automotive disc brakes are "vented," that is, the braking
>> surfaces are separated by a webbing of cast iron intended to have
>> air pass through. High-performance rotors are also cross-drilled
>> and/or slotted.
>
>
> I think you'll find that they are not vented but rather solid disks
> with no holes.

Not true at all.

> The cross drilling is found only on vehicles tauted
> to be high performance while no passenger sedan has cross drilling
> that has no technical advantage but is a relic of the days when brake
> fade was believed to be caused by out-gassing of brake shoes to
> generate a gas bearing. The holes allow that imaginary gas to
> escape.

True, but all but very light and/or inexpensive cars still use vented
rotors, at least on the front. you are confusing cross-drilling and/or
slotting with simple venting, which is a common feature of nearly all
automotive disc brakes. Look at a disc edge-on, you will see that it is
not solid but is essentially two solid braking surfaces connected by a
webbing and with lots of air space in between. That is what is commonly
known as a "vented" rotor.

> I worked in brake design with Girling and ATE in the years when the
> auto industry was changing to disks and was amazed at the amount of
> myth and lore surrounding brakes.

I don't mean to be insulting, but that surprises me given the
inaccuracies in your post. Although that would explain your
unfamiliarity with vented rotors, as AFAIR at least the Studebaker
applications of the first Girling brakes did in fact use solid rotors.
I would assume that other applications of those brakes did as well as
I'm not aware of any significant variations on the caliper design.

nate

--
replace "roosters" with "cox" to reply.
http://members.cox.net/njnagel

[[email protected]]

Nate Nagel wrote:

>>>>> Lots of cars didn't used to have servo assistance on the
>>>>> brakes. All the force and work required to brake came from your
>>>>> leg. And yet you could slow down a tonne of car from 70mph like
>>>>> that.

>>>> Drum brakes used massive self servo action to achieve useful
>>>> braking. Because that effect is highly unpredictable, they had
>>>> both lock-up and fade. That is why we use disks today. You may
>>>> recall that this was discussed here at great length.

>>> I don't understand why you consider that action "highly
>>> unpredictable" it's simply speed dependent. Sure they lock up if
>>> you stomp on 'em but so will boosted discs. The fade comes from
>>> the inability of the shoes and drum to shed heat as effectively as
>>> discs where all the parts are out in the open and in some racing
>>> applications even have forced air ducted over them for additional
>>> cooling.

>> I think you don't know the history of the drum brake. It's self
>> servo action is laid out about a specific friction coefficient such
>> that when it is a bit high, brakes lock up (even after taking the
>> foot off the pedal)

> Which is not an issue on any automotive application, as if anything,
> current non-asbestos linings have an even lower coefficient of
> friction than the original linings around which the brake system was
> designed. I have seen some high-performance linings made available
> for various vintage drum brake setups (presumably for vintage
> racing) and have not ever heard of this happening in practice.

>> and when it is a bit low from heating, there is essentially no brake
>> at all, resulting in run-aways on mountain roads.

The servo effect is what makes the drum brake respond poorly and why,
if you read the Wiki article, no RR ever used drum brakes, skidding a
wheel being a major loss.

> That much is true. Of course this can also happen with discs, if you
> abuse them enough, but discs cool down *much* faster than drums given
> that the friction surface is in direct contact with cooling air, the
> discs have a higher surface area to mass ratio, and that the calipers
> and at least portions of the linings are also in closer proximity to
> cooling air than in a drum brake.

It cannot happen with disks. The relation of the friction coefficient
and brake retardation is linear so the 5% change in friction that
formerly cause total brake failure, the disk sees a 5% change. It's
much like boiling engines in cars. That they don't boil today is not
because they have better radiators, but because they have a
non-leaking water pump seal and don't lose coolant.

http://en.wikipedia.org/wiki/Engine_cooling#Why_automobile_engines_were_air-cooled

>>> Old manual drum brakes are actually quite pleasant to drive on, so
>>> long as you're not racing or driving fast through the mountains.
>>> IMHO they have a much better pedal feel than all but the best new
>>> disc brakes; certainly more direct as there is a direct hydraulic
>>> connection between foot and shoes with only a very few, simple
>>> mechanical parts in between.

>> Oh nostalgia for things that weren't. Read:

http://en.wikipedia.org/wiki/Brake_fade#Fade_in_drum_brakes

> Seeing as I actually own and (occasionally) drive a '55 Studebaker
> coupe equipped with the (excellent) factory equipment brakes, with
> the only upgrade being the addition of finned drums from a later
> model car, I can say that they certainly aren't anywhere near the
> death-dealing devices that you seem to be making them out to be.
> The three major shortcomings of drum brakes in general are 1) brakes
> often undersized for the vehicle, exacerbating other problems (not
> an issue on my car, but, say, the 9" front drums on an old Dart are
> an insult to common sense.) 2) Cooling - drum brakes do retain heat
> far more so than do discs, resulting in earlier fading. 3) single
> circuit master cylinders can result in complete brake system failure
> with one single hydraulic failure. Not an issue with the drums
> themselves, but legal until the late 60's and therefore common on
> most vehicles you'll find with four wheel drum brakes.

I take it you are saying that the auto companies of the world are
barking up the wrong tree when they dumped the drum brake. That's a
bit far fetched. Drum brakes are non-linear and unreliable.

http://tinyurl.com/jhiu

>>>>> The difficult part is getting rid of all the heat that the
>>>>> brakes are converting the bike's kinetic energy into.

>> That's why heavy trucks still use drum brakes, drums having large
>> surface to reject heat by forced convection. Highways have long dual
>> tired skid marks because the response to brake application cannot be
>> well controlled with drum brakes.

> I believe that they still use drums because they're easier to work with
> in an air brake application. They still don't shed heat nearly as well
> as to discs. I suspect many of those skid marks are also the result of
> air system failures, not panic stops gone bad.

You are guessing. Brakes are used for performance and disks large
enough to control a large truck will not fit inside standard truck
wheels. That's why disks are not used there.

>>>> Apparently the bicycle industry is not addressing that part of
>>>> the problem when the surface area and thermal mass their gossamer
>>>> rings of steel have. I have asked brake manufacturers why their
>>>> disks are mostly air with a thin pattern of thin steel between.
>>>> For cooling is the answer. Maybe they should tell the automotive
>>>> and railway people about their theory.

>>> ??? most automotive disc brakes are "vented," that is, the braking
>>> surfaces are separated by a webbing of cast iron intended to have
>>> air pass through. High-performance rotors are also cross-drilled
>>> and/or slotted.

>> I think you'll find that they are not vented but rather solid disks
>> with no holes.

> Not true at all.

OK! You keep making these claims and show no reason or reference for
them. Just inspect BMW cars and note that even their large "sport
cars"do not have holes in the disks.

>> The cross drilling is found only on vehicles tauted to be high
>> performance while no passenger sedan has cross drilling that has no
>> technical advantage but is a relic of the days when brake fade was
>> believed to be caused by out-gassing of brake shoes to generate a
>> gas bearing. The holes allow that imaginary gas to escape.

> True, but all but very light and/or inexpensive cars still use
> vented rotors, at least on the front. you are confusing
> cross-drilling and/or slotting with simple venting, which is a
> common feature of nearly all automotive disc brakes. Look at a disc
> edge-on, you will see that it is not solid but is essentially two
> solid braking surfaces connected by a webbing and with lots of air
> space in between. That is what is commonly known as a "vented"
> rotor.

Name a few please.

>> I worked in brake design with Girling and ATE in the years when the
>> auto industry was changing to disks and was amazed at the amount of
>> myth and lore surrounding brakes.

> I don't mean to be insulting, but that surprises me given the
> inaccuracies in your post. Although that would explain your
> unfamiliarity with vented rotors, as AFAIR at least the Studebaker
> applications of the first Girling brakes did in fact use solid rotors.
> I would assume that other applications of those brakes did as well as
> I'm not aware of any significant variations on the caliper design.

You are not trying hard enough to not be insulting. Your unsupported
claims are in themselves insulting in facer of evidence to the
contrary. The subject here was to cross drilling with holed through
the disk faces. RR disks are all internally radially vented in the
disk casting.

http://www.merriam-webster.com/dictionary/disk

Jobst Brandt

[Nate Nagel[_2_]]

wrote:
> Nate Nagel wrote:
>
>
>>>>>>Lots of cars didn't used to have servo assistance on the
>>>>>>brakes. All the force and work required to brake came from your
>>>>>>leg. And yet you could slow down a tonne of car from 70mph like
>>>>>>that.
>
>
>>>>>Drum brakes used massive self servo action to achieve useful
>>>>>braking. Because that effect is highly unpredictable, they had
>>>>>both lock-up and fade. That is why we use disks today. You may
>>>>>recall that this was discussed here at great length.
>
>
>>>>I don't understand why you consider that action "highly
>>>>unpredictable" it's simply speed dependent. Sure they lock up if
>>>>you stomp on 'em but so will boosted discs. The fade comes from
>>>>the inability of the shoes and drum to shed heat as effectively as
>>>>discs where all the parts are out in the open and in some racing
>>>>applications even have forced air ducted over them for additional
>>>>cooling.
>
>
>>>I think you don't know the history of the drum brake. It's self
>>>servo action is laid out about a specific friction coefficient such
>>>that when it is a bit high, brakes lock up (even after taking the
>>>foot off the pedal)
>
>
>>Which is not an issue on any automotive application, as if anything,
>>current non-asbestos linings have an even lower coefficient of
>>friction than the original linings around which the brake system was
>>designed. I have seen some high-performance linings made available
>>for various vintage drum brake setups (presumably for vintage
>>racing) and have not ever heard of this happening in practice.
>
>
>>>and when it is a bit low from heating, there is essentially no brake
>>>at all, resulting in run-aways on mountain roads.
>
>
> The servo effect is what makes the drum brake respond poorly and why,
> if you read the Wiki article, no RR ever used drum brakes, skidding a
> wheel being a major loss.
>
>
>>That much is true. Of course this can also happen with discs, if you
>>abuse them enough, but discs cool down *much* faster than drums given
>>that the friction surface is in direct contact with cooling air, the
>>discs have a higher surface area to mass ratio, and that the calipers
>>and at least portions of the linings are also in closer proximity to
>>cooling air than in a drum brake.
>
>
> It cannot happen with disks. The relation of the friction coefficient
> and brake retardation is linear so the 5% change in friction that
> formerly cause total brake failure, the disk sees a 5% change. It's
> much like boiling engines in cars. That they don't boil today is not
> because they have better radiators, but because they have a
> non-leaking water pump seal and don't lose coolant.
>
> http://en.wikipedia.org/wiki/Engine_cooling#Why_automobile_engines_were_air-cooled
>

a 5% change in brake friction will not cause a "total brake failure" on
any decent automotive brake system. Now it may cause more than 5% loss
on a servo-action system, but not "total."

>
>>>>Old manual drum brakes are actually quite pleasant to drive on, so
>>>>long as you're not racing or driving fast through the mountains.
>>>>IMHO they have a much better pedal feel than all but the best new
>>>>disc brakes; certainly more direct as there is a direct hydraulic
>>>>connection between foot and shoes with only a very few, simple
>>>>mechanical parts in between.
>
>
>>>Oh nostalgia for things that weren't. Read:
>
>
> http://en.wikipedia.org/wiki/Brake_fade#Fade_in_drum_brakes
>
>
>>Seeing as I actually own and (occasionally) drive a '55 Studebaker
>>coupe equipped with the (excellent) factory equipment brakes, with
>>the only upgrade being the addition of finned drums from a later
>>model car, I can say that they certainly aren't anywhere near the
>>death-dealing devices that you seem to be making them out to be.
>>The three major shortcomings of drum brakes in general are 1) brakes
>>often undersized for the vehicle, exacerbating other problems (not
>>an issue on my car, but, say, the 9" front drums on an old Dart are
>>an insult to common sense.) 2) Cooling - drum brakes do retain heat
>>far more so than do discs, resulting in earlier fading. 3) single
>>circuit master cylinders can result in complete brake system failure
>>with one single hydraulic failure. Not an issue with the drums
>>themselves, but legal until the late 60's and therefore common on
>>most vehicles you'll find with four wheel drum brakes.
>
>
> I take it you are saying that the auto companies of the world are
> barking up the wrong tree when they dumped the drum brake. That's a
> bit far fetched. Drum brakes are non-linear and unreliable.
>
> http://tinyurl.com/jhiu
>

No, I'm saying that while discs are definitely an improvement, drums are
not nearly as dangerous and unacceptable, at least in the better
automotive implementations, as you make them out to be.

How do you explain, if the servo-action is responsible for the effects
that you claim, that some automotive drums did *not* use servo-action
brakes and still exhibited similar fade? It's the heat, plain and
simple. That was the biggest downfall of drums, and it's the biggest
advantage of discs. To a lesser extent the increased linearity of brake
torque vs. line pressure that you did mention. That is not to say that
there aren't downsides - the biggest *disadvantage* of discs is the
necessity to install a power booster on all but the lightest cars, as
you need significantly more line pressure to develop the same brake
torque as the same size drum brake. This is what I was alluding to when
I mentioned the improved pedal feel of drums - the vacuum booster
commonly used does make for a far less direct feel on the brake pedal.

>
>>>>>>The difficult part is getting rid of all the heat that the
>>>>>>brakes are converting the bike's kinetic energy into.
>
>
>>>That's why heavy trucks still use drum brakes, drums having large
>>>surface to reject heat by forced convection. Highways have long dual
>>> tired skid marks because the response to brake application cannot be
>>> well controlled with drum brakes.
>
>
>>I believe that they still use drums because they're easier to work with
>>in an air brake application. They still don't shed heat nearly as well
>>as to discs. I suspect many of those skid marks are also the result of
>>air system failures, not panic stops gone bad.
>
>
> You are guessing. Brakes are used for performance and disks large
> enough to control a large truck will not fit inside standard truck
> wheels. That's why disks are not used there.

I actually *have* seen discs on heavy trucks... not nearly as many as
drums, but they are out there.

>
>>>>>Apparently the bicycle industry is not addressing that part of
>>>>>the problem when the surface area and thermal mass their gossamer
>>>>>rings of steel have. I have asked brake manufacturers why their
>>>>>disks are mostly air with a thin pattern of thin steel between.
>>>>>For cooling is the answer. Maybe they should tell the automotive
>>>>>and railway people about their theory.
>
>
>>>>??? most automotive disc brakes are "vented," that is, the braking
>>>> surfaces are separated by a webbing of cast iron intended to have
>>>>air pass through. High-performance rotors are also cross-drilled
>>>>and/or slotted.
>
>
>>>I think you'll find that they are not vented but rather solid disks
>>>with no holes.
>
>
>>Not true at all.
>
>
> OK! You keep making these claims and show no reason or reference for
> them. Just inspect BMW cars and note that even their large "sport
> cars"do not have holes in the disks.
>

But they are still vented.

>
>>>The cross drilling is found only on vehicles tauted to be high
>>>performance while no passenger sedan has cross drilling that has no
>>>technical advantage but is a relic of the days when brake fade was
>>>believed to be caused by out-gassing of brake shoes to generate a
>>>gas bearing. The holes allow that imaginary gas to escape.
>
>
>>True, but all but very light and/or inexpensive cars still use
>>vented rotors, at least on the front. you are confusing
>>cross-drilling and/or slotting with simple venting, which is a
>>common feature of nearly all automotive disc brakes. Look at a disc
>>edge-on, you will see that it is not solid but is essentially two
>>solid braking surfaces connected by a webbing and with lots of air
>>space in between. That is what is commonly known as a "vented"
>>rotor.
>
>
> Name a few please.

Any modern car equipped with disc brakes. In my driveway, a Chevy
Impala (icky company car) a Porsche 944 and a Ford F-150. All have
vented discs, at least on the front.

The last car I saw *without* vented front discs was my mom's '86 VW
Golf. It did have solid front discs.

>
>>>I worked in brake design with Girling and ATE in the years when the
>>>auto industry was changing to disks and was amazed at the amount of
>>>myth and lore surrounding brakes.
>
>
>>I don't mean to be insulting, but that surprises me given the
>>inaccuracies in your post. Although that would explain your
>>unfamiliarity with vented rotors, as AFAIR at least the Studebaker
>>applications of the first Girling brakes did in fact use solid rotors.
>>I would assume that other applications of those brakes did as well as
>>I'm not aware of any significant variations on the caliper design.
>
>
> You are not trying hard enough to not be insulting. Your unsupported
> claims are in themselves insulting in facer of evidence to the
> contrary. The subject here was to cross drilling with holed through
> the disk faces. RR disks are all internally radially vented in the
> disk casting.
>
> http://www.merriam-webster.com/dictionary/disk
>
> Jobst Brandt

At this point, I can't even determine if you understand the difference
between venting and drilling. If you can't keep your terminology
straight there's no point in continuing this discussion.

nate

--
replace "roosters" with "cox" to reply.
http://members.cox.net/njnagel

[[email protected]]

On May 2, 2:50 pm, N8N > wrote:
> On May 1, 7:49 pm, wrote:
>
> > Drum brakes used massive self servo action to achieve useful braking.
> > Because that effect is highly unpredictable, they had both lock-up and
> > fade. That is why we use disks today. You may recall that this was
> > discussed here at great length.
>
> I don't understand why you consider that action "highly unpredictable"
> it's simply speed dependent. Sure they lock up if you stomp on 'em
> but so will boosted discs. The fade comes from the inability of the
> shoes and drum to shed heat as effectively as discs where all the
> parts are out in the open and in some racing applications even have
> forced air ducted over them for additional cooling. Old manual drum
> brakes are actually quite pleasant to drive on, so long as you're not
> racing or driving fast through the mountains. IMHO they have a much
> better pedal feel than all but the best new disc brakes; certainly
> more direct as there is a direct hydraulic connection between foot and
> shoes with only a very few, simple mechanical parts in between.

Nate, it sounds to me that your evaluation of "feel" is influenced
unduly by your examination of parts diagrams. You see what you think
is a "more direct connection," therefore you think drum brakes feel
better.

Drum brakes are inherently less predictable. Two personal examples:

First, I as a teenager in the '60s, I drove an old Fiat sedan. It had
drum brakes that appeared oversized for its weight. I decided to test
them to see if they would fade, by accelerating to about 60 mph and
stopping hard, repeatedly.

They did fade - but not as I imagined, by simply requiring more pedal
pressure. On about the third stop, the car suddenly swerved violently
side to side. It was barely controllable, and extremely scary.

Second, I still occasionally ride a 1972 BMW motorcycle, with double
leading shoe front drum brake. "Double leading shoe" means the built-
in servo effect works for me only in the forward direction. On a
certain steep hill with a traffic light, the front brak is barely able
to keep the bike from rolling backwards, because friction at the
braking surface acts to remove braking force.

The latter isn't particularly important, I suppose, but it does
indicate how dependent this system is on the friction coefficient.
The former indicates the same, but in a much more dangerous manner. I
assume one front brake faded before the other - that is, generated
less friction; but the sudden loss of servo effect was violent and
unpredictable. It was much different than merely "speed dependent,"
as you claim.

Drum brakes are gone from cars (at least, in front) for very good
reasons.

- Frank Krygowski

[Clive George]

"Nate Nagel" > wrote in message
...

>>> ??? most automotive disc brakes are "vented," that is, the braking
>>> surfaces are separated by a webbing of cast iron intended to have
>>> air pass through. High-performance rotors are also cross-drilled
>>> and/or slotted.
>>
>>
>> I think you'll find that they are not vented but rather solid disks with
>> no holes.
>
> Not true at all.

I reckon he's probably right - vented disks aren't the norm here. Faster and
bigger stuff has them, but plain old solid rotors rule for normal cars.

cheers,
clive

[Clive George]

> wrote in message
...

> You are guessing. Brakes are used for performance and disks large
> enough to control a large truck will not fit inside standard truck
> wheels. That's why disks are not used there.

I believe trucks are moving to disks over here. Dunno if they're inboard or
not, but it's happening. Of course the USian truck industry is very
technologically conservative, so I'd not be surprised if they were a long
way behing.

cheers,
clive

[Clive George]

"Nate Nagel" > wrote in message
...

> This is what I was alluding to when I mentioned the improved pedal feel of
> drums - the vacuum booster commonly used does make for a far less direct
> feel on the brake pedal.

You might find driving a power-braked car amusing - on a proper citroen, the
pedal doesn't move (noticably), but the braking is still proportional to how
hard you press. Coming from an over-assisted conventional car was an
interesting reminder of the difference.

> Any modern car equipped with disc brakes. In my driveway, a Chevy Impala
> (icky company car) a Porsche 944 and a Ford F-150. All have vented discs,
> at least on the front.

Many over here don't have vented. My CX had them (all round :-) ), but
nothing else I've owned. The stuff you've just mentioned comes under "bigger
or faster than normal". Of course with the weight inflation of cars, they're
getting rather more common...

cheers,
clive

[[email protected]]

Nate Nagel wrote:

>>>>>>> Lots of cars didn't used to have servo assistance on the
>>>>>>> brakes. All the force and work required to brake came from
>>>>>>> your leg. And yet you could slow down a tonne of car from
>>>>>>> 70mph like that.

>>>>>> Drum brakes used massive self servo action to achieve useful
>>>>>> braking. Because that effect is highly unpredictable, they had
>>>>>> both lock-up and fade. That is why we use disks today. You
>>>>>> may recall that this was discussed here at great length.

>>>>> I don't understand why you consider that action "highly
>>>>> unpredictable" it's simply speed dependent. Sure they lock up
>>>>> if you stomp on 'em but so will boosted discs. The fade comes
>>>>> from the inability of the shoes and drum to shed heat as
>>>>> effectively as discs where all the parts are out in the open and
>>>>> in some racing applications even have forced air ducted over
>>>>> them for additional cooling.

>>>> I think you don't know the history of the drum brake. It's self
>>>> servo action is laid out about a specific friction coefficient
>>>> such that when it is a bit high, brakes lock up (even after
>>>> taking the foot off the pedal)

>>> Which is not an issue on any automotive application, as if
>>> anything, current non-asbestos linings have an even lower
>>> coefficient of friction than the original linings around which the
>>> brake system was designed. I have seen some high-performance
>>> linings made available for various vintage drum brake setups
>>> (presumably for vintage racing) and have not ever heard of this
>>> happening in practice.

>>>> and when it is a bit low from heating, there is essentially no
>>>> brake at all, resulting in run-aways on mountain roads.

>> The servo effect is what makes the drum brake respond poorly and
>> why, if you read the Wiki article, no RR ever used drum brakes,
>> skidding a wheel being a major loss.

>>> That much is true. Of course this can also happen with discs, if
>>> you abuse them enough, but discs cool down *much* faster than
>>> drums given that the friction surface is in direct contact with
>>> cooling air, the discs have a higher surface area to mass ratio,
>>> and that the calipers and at least portions of the linings are
>>> also in closer proximity to cooling air than in a drum brake.

>>> It cannot happen with disks. The relation of the friction
>>> coefficient and brake retardation is linear so the 5% change in
>>> friction that formerly cause total brake failure, the disk sees
>>> a 5% change. It's much like boiling engines in cars. That
>>> they don't boil today is not because they have better
>>> radiators, but because they have a non-leaking water pump seal
>>> and don't lose coolant.

http://en.wikipedia.org/wiki/Engine_cooling#Why_automobile_engines_were_air-cooled

> a 5% change in brake friction will not cause a "total brake failure"
> on any decent automotive brake system. Now it may cause more than
> 5% loss on a servo-action system, but not "total."

>>>>> Old manual drum brakes are actually quite pleasant to drive on,
>>>>> so long as you're not racing or driving fast through the
>>>>> mountains. IMHO they have a much better pedal feel than all but
>>>>> the best new disc brakes; certainly more direct as there is a
>>>>> direct hydraulic connection between foot and shoes with only a
>>>>> very few, simple mechanical parts in between.

>>>> Oh nostalgia for things that weren't. Read:

http://en.wikipedia.org/wiki/Brake_fade#Fade_in_drum_brakes

>>> Seeing as I actually own and (occasionally) drive a '55 Studebaker
>>> coupe equipped with the (excellent) factory equipment brakes, with
>>> the only upgrade being the addition of finned drums from a later
>>> model car, I can say that they certainly aren't anywhere near the
>>> death-dealing devices that you seem to be making them out to be.
>>> The three major shortcomings of drum brakes in general are 1)
>>> brakes often undersized for the vehicle, exacerbating other
>>> problems (not an issue on my car, but, say, the 9" front drums on
>>> an old Dart are an insult to common sense.) 2) Cooling - drum
>>> brakes do retain heat far more so than do discs, resulting in
>>> earlier fading. 3) single circuit master cylinders can result in
>>> complete brake system failure with one single hydraulic failure.
>>> Not an issue with the drums themselves, but legal until the late
>>> 60's and therefore common on most vehicles you'll find with four
>>> wheel drum brakes.

>> I take it you are saying that the auto companies of the world are
>> barking up the wrong tree when they dumped the drum brake. That's
>> a bit far fetched. Drum brakes are non-linear and unreliable.

http://tinyurl.com/jhiu

> No, I'm saying that while discs are definitely an improvement, drums
> are not nearly as dangerous and unacceptable, at least in the better
> automotive implementations, as you make them out to be.

> How do you explain, if the servo-action is responsible for the
> effects that you claim, that some automotive drums did *not* use
> servo-action brakes and still exhibited similar fade? It's the
> heat, plain and simple. That was the biggest downfall of drums, and
> it's the biggest advantage of discs. To a lesser extent the
> increased linearity of brake torque vs. line pressure that you did
> mention. That is not to say that there aren't downsides - the
> biggest *disadvantage* of discs is the necessity to install a power
> booster on all but the lightest cars, as you need significantly more
> line pressure to develop the same brake torque as the same size drum
> brake. This is what I was alluding to when I mentioned the improved
> pedal feel of drums - the vacuum booster commonly used does make for
> a far less direct feel on the brake pedal.

When the brake application force is in the direction of drum rotation,
as it must be with drum brakes, then there is a self energising
effect. Proof of that is the rum brakes lock up at times when the
friction coefficient is slightly higher than the design level. All
deum brakes have servo effect. If you have worked on drum brakes you
should have noticed that they are designated leading shoe brakes, that
is that the activating hydraulic piston is pushing in the direction of
drum rotation.

>>>>>>> The difficult part is getting rid of all the heat that the
>>>>>>> brakes are converting the bike's kinetic energy into.

>>>> That's why heavy trucks still use drum brakes, drums having large
>>>> surface to reject heat by forced convection. Highways have long
>>>> dual tired skid marks because the response to brake application
>>>> cannot be well controlled with drum brakes.

>>> I believe that they still use drums because they're easier to work
>>> with in an air brake application. They still don't shed heat
>>> nearly as well as to discs. I suspect many of those skid marks
>>> are also the result of air system failures, not panic stops gone
>>> bad.

>> You are guessing. Brakes are used for performance and disks large
>> enough to control a large truck will not fit inside standard truck
>> wheels. That's why disks are not used there.

> I actually *have* seen discs on heavy trucks... not nearly as many
> as drums, but they are out there.

You may have seen them on tractors of semi trailer rigs, but not on
the tandem dual dive axles or the semitrailer where heavy braking
occurs.

>>>>>> Apparently the bicycle industry is not addressing that part of
>>>>>> the problem when the surface area and thermal mass their
>>>>>> gossamer rings of steel have. I have asked brake manufacturers
>>>>>> why their disks are mostly air with a thin pattern of thin
>>>>>> steel between. For cooling is the answer. Maybe they should
>>>>>> tell the automotive and railway people about their theory.

>>>>> ??? most automotive disc brakes are "vented," that is, the
>>>>> braking surfaces are separated by a webbing of cast iron
>>>>> intended to have air pass through. High-performance rotors are
>>>>> also cross-drilled and/or slotted.

>>>> I think you'll find that they are not vented but rather solid
>>>> disks with no holes.

>>> Not true at all.

>> OK! You keep making these claims and show no reason or reference
>> for them. Just inspect BMW cars and note that even their large
>> "sport cars"do not have holes in the disks.

> But they are still vented.

Look at all the high performance (BMW, Mercedes, Caddillac, Chrysler,
Cheverolet, Buick,...) cars and you will see they have no holes. You
must be assuming car companies are taking safety lightly if they sell
the largest part of their cars with, as you claim, inferior disks that
have no holes.

>>>> The cross drilling is found only on vehicles tauted to be high
>>>> performance while no passenger sedan has cross drilling that has
>>>> no technical advantage but is a relic of the days when brake fade
>>>> was believed to be caused by out-gassing of brake shoes to
>>>> generate a gas bearing. The holes allow that imaginary gas to
>>>> escape.

>>> True, but all but very light and/or inexpensive cars still use
>>> vented rotors, at least on the front. you are confusing
>>> cross-drilling and/or slotting with simple venting, which is a
>>> common feature of nearly all automotive disc brakes. Look at a
>>> disc edge-on, you will see that it is not solid but is essentially
>>> two solid braking surfaces connected by a webbing and with lots of
>>> air space in between. That is what is commonly known as a
>>> "vented" rotor.

>> Name a few please.

> Any modern car equipped with disc brakes. In my driveway, a Chevy
> Impala (icky company car) a Porsche 944 and a Ford F-150. All have
> vented discs, at least on the front.

Not the new ones aold today. Exactly these are proof that there is no
benefit to the cross drillings in the disks of "sports cars".

> The last car I saw *without* vented front discs was my mom's '86 VW
> Golf. It did have solid front discs.

You use the term "vemnted" without definition. What do you mean?

>>>> I worked in brake design with Girling and ATE in the years when
>>>> the auto industry was changing to disks and was amazed at the
>>>> amount of myth and lore surrounding brakes.

>>> I don't mean to be insulting, but that surprises me given the
>>> inaccuracies in your post. Although that would explain your
>>> unfamiliarity with vented rotors, as AFAIR at least the Studebaker
>>> applications of the first Girling brakes did in fact use solid
>>> rotors. I would assume that other applications of those brakes
>>> did as well as I'm not aware of any significant variations on the
>>> caliper design.

>> You are not trying hard enough to not be insulting. Your
>> unsupported claims are in themselves insulting in facer of evidence
>> to the contrary. The subject here was to cross drilling with holed
>> through the disk faces. RR disks are all internally radially
>> vented in the disk casting.

http://www.merriam-webster.com/dictionary/disk

> At this point, I can't even determine if you understand the
> difference between venting and drilling. If you can't keep your
> terminology straight there's no point in continuing this discussion.

At this point I suggest you heed your request for definition of disk
form. I detect you are trying to make a technical educational course
about disk brake, not understanding the basic difference between disks
and drums. I am not ready to outline a course on disk brakes here.

Jobst Brandt

[Nate Nagel[_2_]]

Clive George wrote:
> "Nate Nagel" > wrote in message
> ...
>
>> This is what I was alluding to when I mentioned the improved pedal
>> feel of drums - the vacuum booster commonly used does make for a far
>> less direct feel on the brake pedal.
>
>
> You might find driving a power-braked car amusing - on a proper citroen,
> the pedal doesn't move (noticably), but the braking is still
> proportional to how hard you press. Coming from an over-assisted
> conventional car was an interesting reminder of the difference.
>
>> Any modern car equipped with disc brakes. In my driveway, a Chevy
>> Impala (icky company car) a Porsche 944 and a Ford F-150. All have
>> vented discs, at least on the front.
>
>
> Many over here don't have vented. My CX had them (all round :-) ), but
> nothing else I've owned. The stuff you've just mentioned comes under
> "bigger or faster than normal". Of course with the weight inflation of
> cars, they're getting rather more common...
>
> cheers,
> clive

If you'd consider any of those cars "faster than normal" I have the
greatest sympathy for you. Of course Vlad the Impala and the pickup
truck are also quite large, and only one of those two has a good reason
for being so. A 944 has many redeeming qualities, but sparkling
acceleration isn't one of them.

Oddly enough, likely the fastest car I own (I don't know for sure, I
haven't fully tested its capabilities) is also the one with four wheel
drum brakes.

nate

--
replace "roosters" with "cox" to reply.
http://members.cox.net/njnagel

[Kerry Montgomery]

> wrote in message
...
> Nate Nagel wrote:
>
>>>>>>>> Lots of cars didn't used to have servo assistance on the
>>>>>>>> brakes. All the force and work required to brake came from
>>>>>>>> your leg. And yet you could slow down a tonne of car from
>>>>>>>> 70mph like that.
>
>>>>>>> Drum brakes used massive self servo action to achieve useful
>>>>>>> braking. Because that effect is highly unpredictable, they had
>>>>>>> both lock-up and fade. That is why we use disks today. You
>>>>>>> may recall that this was discussed here at great length.
>
>>>>>> I don't understand why you consider that action "highly
>>>>>> unpredictable" it's simply speed dependent. Sure they lock up
>>>>>> if you stomp on 'em but so will boosted discs. The fade comes
>>>>>> from the inability of the shoes and drum to shed heat as
>>>>>> effectively as discs where all the parts are out in the open and
>>>>>> in some racing applications even have forced air ducted over
>>>>>> them for additional cooling.
>
>>>>> I think you don't know the history of the drum brake. It's self
>>>>> servo action is laid out about a specific friction coefficient
>>>>> such that when it is a bit high, brakes lock up (even after
>>>>> taking the foot off the pedal)
>
>>>> Which is not an issue on any automotive application, as if
>>>> anything, current non-asbestos linings have an even lower
>>>> coefficient of friction than the original linings around which the
>>>> brake system was designed. I have seen some high-performance
>>>> linings made available for various vintage drum brake setups
>>>> (presumably for vintage racing) and have not ever heard of this
>>>> happening in practice.
>
>>>>> and when it is a bit low from heating, there is essentially no
>>>>> brake at all, resulting in run-aways on mountain roads.
>
>>> The servo effect is what makes the drum brake respond poorly and
>>> why, if you read the Wiki article, no RR ever used drum brakes,
>>> skidding a wheel being a major loss.
>
>>>> That much is true. Of course this can also happen with discs, if
>>>> you abuse them enough, but discs cool down *much* faster than
>>>> drums given that the friction surface is in direct contact with
>>>> cooling air, the discs have a higher surface area to mass ratio,
>>>> and that the calipers and at least portions of the linings are
>>>> also in closer proximity to cooling air than in a drum brake.
>
>>>> It cannot happen with disks. The relation of the friction
>>>> coefficient and brake retardation is linear so the 5% change in
>>>> friction that formerly cause total brake failure, the disk sees
>>>> a 5% change. It's much like boiling engines in cars. That
>>>> they don't boil today is not because they have better
>>>> radiators, but because they have a non-leaking water pump seal
>>>> and don't lose coolant.
>
> http://en.wikipedia.org/wiki/Engine_cooling#Why_automobile_engines_were_air-cooled
>
>> a 5% change in brake friction will not cause a "total brake failure"
>> on any decent automotive brake system. Now it may cause more than
>> 5% loss on a servo-action system, but not "total."
>
>>>>>> Old manual drum brakes are actually quite pleasant to drive on,
>>>>>> so long as you're not racing or driving fast through the
>>>>>> mountains. IMHO they have a much better pedal feel than all but
>>>>>> the best new disc brakes; certainly more direct as there is a
>>>>>> direct hydraulic connection between foot and shoes with only a
>>>>>> very few, simple mechanical parts in between.
>
>>>>> Oh nostalgia for things that weren't. Read:
>
> http://en.wikipedia.org/wiki/Brake_fade#Fade_in_drum_brakes
>
>>>> Seeing as I actually own and (occasionally) drive a '55 Studebaker
>>>> coupe equipped with the (excellent) factory equipment brakes, with
>>>> the only upgrade being the addition of finned drums from a later
>>>> model car, I can say that they certainly aren't anywhere near the
>>>> death-dealing devices that you seem to be making them out to be.
>>>> The three major shortcomings of drum brakes in general are 1)
>>>> brakes often undersized for the vehicle, exacerbating other
>>>> problems (not an issue on my car, but, say, the 9" front drums on
>>>> an old Dart are an insult to common sense.) 2) Cooling - drum
>>>> brakes do retain heat far more so than do discs, resulting in
>>>> earlier fading. 3) single circuit master cylinders can result in
>>>> complete brake system failure with one single hydraulic failure.
>>>> Not an issue with the drums themselves, but legal until the late
>>>> 60's and therefore common on most vehicles you'll find with four
>>>> wheel drum brakes.
>
>>> I take it you are saying that the auto companies of the world are
>>> barking up the wrong tree when they dumped the drum brake. That's
>>> a bit far fetched. Drum brakes are non-linear and unreliable.
>
> http://tinyurl.com/jhiu
>
>> No, I'm saying that while discs are definitely an improvement, drums
>> are not nearly as dangerous and unacceptable, at least in the better
>> automotive implementations, as you make them out to be.
>
>> How do you explain, if the servo-action is responsible for the
>> effects that you claim, that some automotive drums did *not* use
>> servo-action brakes and still exhibited similar fade? It's the
>> heat, plain and simple. That was the biggest downfall of drums, and
>> it's the biggest advantage of discs. To a lesser extent the
>> increased linearity of brake torque vs. line pressure that you did
>> mention. That is not to say that there aren't downsides - the
>> biggest *disadvantage* of discs is the necessity to install a power
>> booster on all but the lightest cars, as you need significantly more
>> line pressure to develop the same brake torque as the same size drum
>> brake. This is what I was alluding to when I mentioned the improved
>> pedal feel of drums - the vacuum booster commonly used does make for
>> a far less direct feel on the brake pedal.
>
> When the brake application force is in the direction of drum rotation,
> as it must be with drum brakes, then there is a self energising
> effect. Proof of that is the rum brakes lock up at times when the
> friction coefficient is slightly higher than the design level. All
> deum brakes have servo effect. If you have worked on drum brakes you
> should have noticed that they are designated leading shoe brakes, that
> is that the activating hydraulic piston is pushing in the direction of
> drum rotation.
>
>>>>>>>> The difficult part is getting rid of all the heat that the
>>>>>>>> brakes are converting the bike's kinetic energy into.
>
>>>>> That's why heavy trucks still use drum brakes, drums having large
>>>>> surface to reject heat by forced convection. Highways have long
>>>>> dual tired skid marks because the response to brake application
>>>>> cannot be well controlled with drum brakes.
>
>>>> I believe that they still use drums because they're easier to work
>>>> with in an air brake application. They still don't shed heat
>>>> nearly as well as to discs. I suspect many of those skid marks
>>>> are also the result of air system failures, not panic stops gone
>>>> bad.
>
>>> You are guessing. Brakes are used for performance and disks large
>>> enough to control a large truck will not fit inside standard truck
>>> wheels. That's why disks are not used there.
>
>> I actually *have* seen discs on heavy trucks... not nearly as many
>> as drums, but they are out there.
>
> You may have seen them on tractors of semi trailer rigs, but not on
> the tandem dual dive axles or the semitrailer where heavy braking
> occurs.
>
>>>>>>> Apparently the bicycle industry is not addressing that part of
>>>>>>> the problem when the surface area and thermal mass their
>>>>>>> gossamer rings of steel have. I have asked brake manufacturers
>>>>>>> why their disks are mostly air with a thin pattern of thin
>>>>>>> steel between. For cooling is the answer. Maybe they should
>>>>>>> tell the automotive and railway people about their theory.
>
>>>>>> ??? most automotive disc brakes are "vented," that is, the
>>>>>> braking surfaces are separated by a webbing of cast iron
>>>>>> intended to have air pass through. High-performance rotors are
>>>>>> also cross-drilled and/or slotted.
>
>>>>> I think you'll find that they are not vented but rather solid
>>>>> disks with no holes.
>
>>>> Not true at all.
>
>>> OK! You keep making these claims and show no reason or reference
>>> for them. Just inspect BMW cars and note that even their large
>>> "sport cars"do not have holes in the disks.
>
>> But they are still vented.
>
> Look at all the high performance (BMW, Mercedes, Caddillac, Chrysler,
> Cheverolet, Buick,...) cars and you will see they have no holes. You
> must be assuming car companies are taking safety lightly if they sell
> the largest part of their cars with, as you claim, inferior disks that
> have no holes.
>
>>>>> The cross drilling is found only on vehicles tauted to be high
>>>>> performance while no passenger sedan has cross drilling that has
>>>>> no technical advantage but is a relic of the days when brake fade
>>>>> was believed to be caused by out-gassing of brake shoes to
>>>>> generate a gas bearing. The holes allow that imaginary gas to
>>>>> escape.
>
>>>> True, but all but very light and/or inexpensive cars still use
>>>> vented rotors, at least on the front. you are confusing
>>>> cross-drilling and/or slotting with simple venting, which is a
>>>> common feature of nearly all automotive disc brakes. Look at a
>>>> disc edge-on, you will see that it is not solid but is essentially
>>>> two solid braking surfaces connected by a webbing and with lots of
>>>> air space in between. That is what is commonly known as a
>>>> "vented" rotor.
>
>>> Name a few please.
>
>> Any modern car equipped with disc brakes. In my driveway, a Chevy
>> Impala (icky company car) a Porsche 944 and a Ford F-150. All have
>> vented discs, at least on the front.
>
> Not the new ones aold today. Exactly these are proof that there is no
> benefit to the cross drillings in the disks of "sports cars".
>
>> The last car I saw *without* vented front discs was my mom's '86 VW
>> Golf. It did have solid front discs.
>
> You use the term "vemnted" without definition. What do you mean?
>
>>>>> I worked in brake design with Girling and ATE in the years when
>>>>> the auto industry was changing to disks and was amazed at the
>>>>> amount of myth and lore surrounding brakes.
>
>>>> I don't mean to be insulting, but that surprises me given the
>>>> inaccuracies in your post. Although that would explain your
>>>> unfamiliarity with vented rotors, as AFAIR at least the Studebaker
>>>> applications of the first Girling brakes did in fact use solid
>>>> rotors. I would assume that other applications of those brakes
>>>> did as well as I'm not aware of any significant variations on the
>>>> caliper design.
>
>>> You are not trying hard enough to not be insulting. Your
>>> unsupported claims are in themselves insulting in facer of evidence
>>> to the contrary. The subject here was to cross drilling with holed
>>> through the disk faces. RR disks are all internally radially
>>> vented in the disk casting.
>
> http://www.merriam-webster.com/dictionary/disk
>
>> At this point, I can't even determine if you understand the
>> difference between venting and drilling. If you can't keep your
>> terminology straight there's no point in continuing this discussion.
>
> At this point I suggest you heed your request for definition of disk
> form. I detect you are trying to make a technical educational course
> about disk brake, not understanding the basic difference between disks
> and drums. I am not ready to outline a course on disk brakes here.
>
> Jobst Brandt

Jobst and Nate,
Just to set some common ground - here is what I think a vented disk brake
rotor looks like:
http://images.outdoorinteractive.net/mgen/530211_oi.jpg
And here is what I think a cross-drilled disk brake rotor looks like:
http://www.camarotech.com/images/BrakeRotor_CrossDrilled.jpg
Kerry

[Nate Nagel[_2_]]

wrote:
> Nate Nagel wrote:
>
>
>>>>>>>>Lots of cars didn't used to have servo assistance on the
>>>>>>>>brakes. All the force and work required to brake came from
>>>>>>>>your leg. And yet you could slow down a tonne of car from
>>>>>>>>70mph like that.
>
>
>>>>>>>Drum brakes used massive self servo action to achieve useful
>>>>>>>braking. Because that effect is highly unpredictable, they had
>>>>>>>both lock-up and fade. That is why we use disks today. You
>>>>>>>may recall that this was discussed here at great length.
>
>
>>>>>>I don't understand why you consider that action "highly
>>>>>>unpredictable" it's simply speed dependent. Sure they lock up
>>>>>>if you stomp on 'em but so will boosted discs. The fade comes
>>>>>>from the inability of the shoes and drum to shed heat as
>>>>>>effectively as discs where all the parts are out in the open and
>>>>>>in some racing applications even have forced air ducted over
>>>>>>them for additional cooling.
>
>
>>>>>I think you don't know the history of the drum brake. It's self
>>>>>servo action is laid out about a specific friction coefficient
>>>>>such that when it is a bit high, brakes lock up (even after
>>>>>taking the foot off the pedal)
>
>
>>>>Which is not an issue on any automotive application, as if
>>>>anything, current non-asbestos linings have an even lower
>>>>coefficient of friction than the original linings around which the
>>>>brake system was designed. I have seen some high-performance
>>>>linings made available for various vintage drum brake setups
>>>>(presumably for vintage racing) and have not ever heard of this
>>>>happening in practice.
>
>
>>>>>and when it is a bit low from heating, there is essentially no
>>>>>brake at all, resulting in run-aways on mountain roads.
>
>
>>>The servo effect is what makes the drum brake respond poorly and
>>>why, if you read the Wiki article, no RR ever used drum brakes,
>>>skidding a wheel being a major loss.
>
>
>>>>That much is true. Of course this can also happen with discs, if
>>>>you abuse them enough, but discs cool down *much* faster than
>>>>drums given that the friction surface is in direct contact with
>>>>cooling air, the discs have a higher surface area to mass ratio,
>>>>and that the calipers and at least portions of the linings are
>>>>also in closer proximity to cooling air than in a drum brake.
>
>
>>>>It cannot happen with disks. The relation of the friction
>>>>coefficient and brake retardation is linear so the 5% change in
>>>>friction that formerly cause total brake failure, the disk sees
>>>>a 5% change. It's much like boiling engines in cars. That
>>>>they don't boil today is not because they have better
>>>>radiators, but because they have a non-leaking water pump seal
>>>>and don't lose coolant.
>
>
> http://en.wikipedia.org/wiki/Engine_cooling#Why_automobile_engines_were_air-cooled
>
>
>>a 5% change in brake friction will not cause a "total brake failure"
>>on any decent automotive brake system. Now it may cause more than
>>5% loss on a servo-action system, but not "total."
>
>
>>>>>>Old manual drum brakes are actually quite pleasant to drive on,
>>>>>>so long as you're not racing or driving fast through the
>>>>>>mountains. IMHO they have a much better pedal feel than all but
>>>>>>the best new disc brakes; certainly more direct as there is a
>>>>>>direct hydraulic connection between foot and shoes with only a
>>>>>>very few, simple mechanical parts in between.
>
>
>>>>>Oh nostalgia for things that weren't. Read:
>
>
> http://en.wikipedia.org/wiki/Brake_fade#Fade_in_drum_brakes
>
>
>>>>Seeing as I actually own and (occasionally) drive a '55 Studebaker
>>>>coupe equipped with the (excellent) factory equipment brakes, with
>>>>the only upgrade being the addition of finned drums from a later
>>>>model car, I can say that they certainly aren't anywhere near the
>>>>death-dealing devices that you seem to be making them out to be.
>>>>The three major shortcomings of drum brakes in general are 1)
>>>>brakes often undersized for the vehicle, exacerbating other
>>>>problems (not an issue on my car, but, say, the 9" front drums on
>>>>an old Dart are an insult to common sense.) 2) Cooling - drum
>>>>brakes do retain heat far more so than do discs, resulting in
>>>>earlier fading. 3) single circuit master cylinders can result in
>>>>complete brake system failure with one single hydraulic failure.
>>>>Not an issue with the drums themselves, but legal until the late
>>>>60's and therefore common on most vehicles you'll find with four
>>>>wheel drum brakes.
>
>
>>>I take it you are saying that the auto companies of the world are
>>>barking up the wrong tree when they dumped the drum brake. That's
>>>a bit far fetched. Drum brakes are non-linear and unreliable.
>
>
> http://tinyurl.com/jhiu
>
>
>>No, I'm saying that while discs are definitely an improvement, drums
>>are not nearly as dangerous and unacceptable, at least in the better
>>automotive implementations, as you make them out to be.
>
>
>>How do you explain, if the servo-action is responsible for the
>>effects that you claim, that some automotive drums did *not* use
>>servo-action brakes and still exhibited similar fade? It's the
>>heat, plain and simple. That was the biggest downfall of drums, and
>>it's the biggest advantage of discs. To a lesser extent the
>>increased linearity of brake torque vs. line pressure that you did
>>mention. That is not to say that there aren't downsides - the
>>biggest *disadvantage* of discs is the necessity to install a power
>>booster on all but the lightest cars, as you need significantly more
>>line pressure to develop the same brake torque as the same size drum
>>brake. This is what I was alluding to when I mentioned the improved
>>pedal feel of drums - the vacuum booster commonly used does make for
>>a far less direct feel on the brake pedal.
>
>
> When the brake application force is in the direction of drum rotation,
> as it must be with drum brakes, then there is a self energising
> effect.

Actually, it doesn't matter which direction, on most brakes. The servo
effect works both ways, but the leading shoe is smaller for reasons of
even wear.

> Proof of that is the rum brakes lock up at times when the
> friction coefficient is slightly higher than the design level.

Ok, so? that's not generally a problem.

> All
> deum brakes have servo effect.

No, there are most definitely non-servo drum brakes. Early Studebaker
drums for example, or some of the odd dual wheel cylinder designs.

> If you have worked on drum brakes you
> should have noticed that they are designated leading shoe brakes, that
> is that the activating hydraulic piston is pushing in the direction of
> drum rotation.

And that is for reasons of even shoe wear. also the wheel cylinder
pushes both ways in the normal drum brake setup, so the servo action can
work in both directions.

>
>>>>>>>>The difficult part is getting rid of all the heat that the
>>>>>>>>brakes are converting the bike's kinetic energy into.
>
>
>>>>>That's why heavy trucks still use drum brakes, drums having large
>>>>>surface to reject heat by forced convection. Highways have long
>>>>>dual tired skid marks because the response to brake application
>>>>>cannot be well controlled with drum brakes.
>
>
>>>>I believe that they still use drums because they're easier to work
>>>>with in an air brake application. They still don't shed heat
>>>>nearly as well as to discs. I suspect many of those skid marks
>>>>are also the result of air system failures, not panic stops gone
>>>>bad.
>
>
>>>You are guessing. Brakes are used for performance and disks large
>>>enough to control a large truck will not fit inside standard truck
>>>wheels. That's why disks are not used there.
>
>
>>I actually *have* seen discs on heavy trucks... not nearly as many
>>as drums, but they are out there.
>
>
> You may have seen them on tractors of semi trailer rigs, but not on
> the tandem dual dive axles or the semitrailer where heavy braking
> occurs.
>
>
>>>>>>>Apparently the bicycle industry is not addressing that part of
>>>>>>>the problem when the surface area and thermal mass their
>>>>>>>gossamer rings of steel have. I have asked brake manufacturers
>>>>>>>why their disks are mostly air with a thin pattern of thin
>>>>>>>steel between. For cooling is the answer. Maybe they should
>>>>>>>tell the automotive and railway people about their theory.
>
>
>>>>>>??? most automotive disc brakes are "vented," that is, the
>>>>>>braking surfaces are separated by a webbing of cast iron
>>>>>>intended to have air pass through. High-performance rotors are
>>>>>>also cross-drilled and/or slotted.
>
>
>>>>>I think you'll find that they are not vented but rather solid
>>>>>disks with no holes.
>
>
>>>>Not true at all.
>
>
>>>OK! You keep making these claims and show no reason or reference
>>>for them. Just inspect BMW cars and note that even their large
>>>"sport cars"do not have holes in the disks.
>
>
>>But they are still vented.
>
>
> Look at all the high performance (BMW, Mercedes, Caddillac, Chrysler,
> Cheverolet, Buick,...) cars and you will see they have no holes. You
> must be assuming car companies are taking safety lightly if they sell
> the largest part of their cars with, as you claim, inferior disks that
> have no holes.

They may not be cross drilled, but they are all vented.

>>>>>The cross drilling is found only on vehicles tauted to be high
>>>>>performance while no passenger sedan has cross drilling that has
>>>>>no technical advantage but is a relic of the days when brake fade
>>>>>was believed to be caused by out-gassing of brake shoes to
>>>>>generate a gas bearing. The holes allow that imaginary gas to
>>>>>escape.
>
>
>>>>True, but all but very light and/or inexpensive cars still use
>>>>vented rotors, at least on the front. you are confusing
>>>>cross-drilling and/or slotting with simple venting, which is a
>>>>common feature of nearly all automotive disc brakes. Look at a
>>>>disc edge-on, you will see that it is not solid but is essentially
>>>>two solid braking surfaces connected by a webbing and with lots of
>>>>air space in between. That is what is commonly known as a
>>>>"vented" rotor.
>
>
>>>Name a few please.
>
>
>>Any modern car equipped with disc brakes. In my driveway, a Chevy
>>Impala (icky company car) a Porsche 944 and a Ford F-150. All have
>>vented discs, at least on the front.
>
>
> Not the new ones aold today. Exactly these are proof that there is no
> benefit to the cross drillings in the disks of "sports cars".

Yes, all of the new ones sold today. They are vented, as I defined
above (and as is common usage.)

>
>>The last car I saw *without* vented front discs was my mom's '86 VW
>>Golf. It did have solid front discs.
>
>
> You use the term "vemnted" without definition. What do you mean?


See above, I defined the common usage of the term when referring to brakes.

>
>>>>>I worked in brake design with Girling and ATE in the years when
>>>>>the auto industry was changing to disks and was amazed at the
>>>>>amount of myth and lore surrounding brakes.
>
>
>>>>I don't mean to be insulting, but that surprises me given the
>>>>inaccuracies in your post. Although that would explain your
>>>>unfamiliarity with vented rotors, as AFAIR at least the Studebaker
>>>>applications of the first Girling brakes did in fact use solid
>>>>rotors. I would assume that other applications of those brakes
>>>>did as well as I'm not aware of any significant variations on the
>>>>caliper design.
>
>
>>>You are not trying hard enough to not be insulting. Your
>>>unsupported claims are in themselves insulting in facer of evidence
>>>to the contrary. The subject here was to cross drilling with holed
>>>through the disk faces. RR disks are all internally radially
>>>vented in the disk casting.
>
>
> http://www.merriam-webster.com/dictionary/disk
>
>
>>At this point, I can't even determine if you understand the
>>difference between venting and drilling. If you can't keep your
>>terminology straight there's no point in continuing this discussion.
>
>
> At this point I suggest you heed your request for definition of disk
> form. I detect you are trying to make a technical educational course
> about disk brake, not understanding the basic difference between disks
> and drums. I am not ready to outline a course on disk brakes here.

I'm afraid I don't need your "technical educational course" - not to do
the credential dick-waving thing, but I too have worked professionally
with braking systems (albeit specifically with ABS software) and
apparently quite a bit more recently than you. You're confusing venting
with cross-drilling, or you're not understanding the terminology that
I'm using which is standard and has been since the late 60's.

nate

--
replace "roosters" with "cox" to reply.
http://members.cox.net/njnagel

[Clive George]

"Kerry Montgomery" > wrote in message
m...

> Jobst and Nate,
> Just to set some common ground - here is what I think a vented disk brake
> rotor looks like:
> http://images.outdoorinteractive.net/mgen/530211_oi.jpg

Yeah, I am coming to the conclusion that Jobst doesn't actually understand
the normal definition of 'vented' - that used by most auto-parts suppliers.

Your picture agrees with me and pretty much everybody else.

cheers,
clive

[Clive George]

"Nate Nagel" > wrote in message
...
> Clive George wrote:
>> "Nate Nagel" > wrote in message
>> ...
>>
>>> This is what I was alluding to when I mentioned the improved pedal feel
>>> of drums - the vacuum booster commonly used does make for a far less
>>> direct feel on the brake pedal.
>>
>>
>> You might find driving a power-braked car amusing - on a proper citroen,
>> the pedal doesn't move (noticably), but the braking is still proportional
>> to how hard you press. Coming from an over-assisted conventional car was
>> an interesting reminder of the difference.
>>
>>> Any modern car equipped with disc brakes. In my driveway, a Chevy
>>> Impala (icky company car) a Porsche 944 and a Ford F-150. All have
>>> vented discs, at least on the front.
>>
>>
>> Many over here don't have vented. My CX had them (all round :-) ), but
>> nothing else I've owned. The stuff you've just mentioned comes under
>> "bigger or faster than normal". Of course with the weight inflation of
>> cars, they're getting rather more common...
>
> If you'd consider any of those cars "faster than normal" I have the
> greatest sympathy for you.

I did carefully say "bigger" first.

> Of course Vlad the Impala and the pickup truck are also quite large, and
> only one of those two has a good reason for being so. A 944 has many
> redeeming qualities, but sparkling acceleration isn't one of them.

Is it broken? 944 wasn't actually _that_ slow, even in N/A form. 137mph top
speed isn't too bad for 1982, and is still faster than many cooking model
cars.

> Oddly enough, likely the fastest car I own (I don't know for sure, I
> haven't fully tested its capabilities) is also the one with four wheel
> drum brakes.

I did have an amusing time recently reading about USian muscle cars - with
hundreds of BHP, but engineered for the 1/4 mile rather than actual speed,
as could be seen by the gearing they came with. Probably a good thing though
given the handling and braking :-)

cheers,
clive

[Edward Dolan]

"Tom Sherman" > wrote in message
...
[...]
> Back in the early days of the 20th Century recumbent revival (e.g.
> Hypercycle, the never produced Avatar 1000,) the designers mistakenly
> thought that some heel/wheel overlap needed to be avoided. Therefore, the
> boom was made very long and the rider was seated almost over the front
> wheel. This led to too flexible booms which made climbing and acceleration
> poor, poor handling - especially when hitting bumps at speed , and the
> bike rotating forward about the front wheel contact patch under hard
> braking.
>
> Modern short=wheelbase recumbent sensibly trade off some heel overlap for
> proper weight distribution and have none of the above flaws. However, some
> of the "experts" tried the earlier designs 25 or 30 years ago and have
> closed their minds to later improvements.

Even so, SWB recumbents do not handle well and tend to be squirrely. They
are fine for around town for a few hours, but they are the pits on day long
rides. Also, heel overlap is not a good idea. Sooner or later it will trip
you up.

Regards,

Ed Dolan the Great - Minnesota
aka
Saint Edward the Great - Order of the Perpetual Sorrows - Minnesota

[Nate Nagel[_2_]]

Clive George wrote:
> "Nate Nagel" > wrote in message
> ...
>
>> Clive George wrote:
>>
>>> "Nate Nagel" > wrote in message
>>> ...
>>>
>>>> This is what I was alluding to when I mentioned the improved pedal
>>>> feel of drums - the vacuum booster commonly used does make for a far
>>>> less direct feel on the brake pedal.
>>>
>>>
>>>
>>> You might find driving a power-braked car amusing - on a proper
>>> citroen, the pedal doesn't move (noticably), but the braking is still
>>> proportional to how hard you press. Coming from an over-assisted
>>> conventional car was an interesting reminder of the difference.
>>>
>>>> Any modern car equipped with disc brakes. In my driveway, a Chevy
>>>> Impala (icky company car) a Porsche 944 and a Ford F-150. All have
>>>> vented discs, at least on the front.
>>>
>>>
>>>
>>> Many over here don't have vented. My CX had them (all round :-) ),
>>> but nothing else I've owned. The stuff you've just mentioned comes
>>> under "bigger or faster than normal". Of course with the weight
>>> inflation of cars, they're getting rather more common...
>>
>>
>> If you'd consider any of those cars "faster than normal" I have the
>> greatest sympathy for you.
>
>
> I did carefully say "bigger" first.
>
>> Of course Vlad the Impala and the pickup truck are also quite large,
>> and only one of those two has a good reason for being so. A 944 has
>> many redeeming qualities, but sparkling acceleration isn't one of them.
>
>
> Is it broken? 944 wasn't actually _that_ slow, even in N/A form. 137mph
> top speed isn't too bad for 1982, and is still faster than many cooking
> model cars.

I don't think they had quite as much power over here as in Europe...
mine's an 88, so had 150-something HP from the factory, and I doubt it's
picked up any extra over the years :) I might have a *slightly* warped
perspective though, as my previous ride was a GTI 1.8T which had Hand of
God Torque(tm) and although it didn't handle as well would just flat out
destroy any 944 (NA) in a straight line.

I would really like to try a turbo 944 some day, but budget etc.

>
>> Oddly enough, likely the fastest car I own (I don't know for sure, I
>> haven't fully tested its capabilities) is also the one with four wheel
>> drum brakes.
>
>
> I did have an amusing time recently reading about USian muscle cars -
> with hundreds of BHP, but engineered for the 1/4 mile rather than actual
> speed, as could be seen by the gearing they came with. Probably a good
> thing though given the handling and braking :-)

yeah, some of the larger ones were borderline irresponsible, e.g.
Hemi-powered midsize MoPars with disc brakes *optional* - a Studebaker
isn't so bad as it is a fairly light car and their drum brakes were
better than most. Handling was never a big priority as even most
"sporty" American cars were really primarily people haulers and long
distance tourers; if you wanted to go around corners fast you needed to
look to something European. The Corvette being the only real notable
mass-market exception that comes to mind...

nate

--
replace "roosters" with "cox" to reply.
http://members.cox.net/njnagel

[Tom Sherman[_2_]]

Edward Dolan wrote:
> "Tom Sherman" > wrote in message
> ...
> [...]
>> Back in the early days of the 20th Century recumbent revival (e.g.
>> Hypercycle, the never produced Avatar 1000,) the designers mistakenly
>> thought that some heel/wheel overlap needed to be avoided. Therefore, the
>> boom was made very long and the rider was seated almost over the front
>> wheel. This led to too flexible booms which made climbing and acceleration
>> poor, poor handling - especially when hitting bumps at speed , and the
>> bike rotating forward about the front wheel contact patch under hard
>> braking.
>>
>> Modern short=wheelbase recumbent sensibly trade off some heel overlap for
>> proper weight distribution and have none of the above flaws. However, some
>> of the "experts" tried the earlier designs 25 or 30 years ago and have
>> closed their minds to later improvements.
>
> Even so, SWB recumbents do not handle well and tend to be squirrely. They
> are fine for around town for a few hours, but they are the pits on day long
> rides.

My short-wheelbase recumbents (RANS Rocket, Earth Cycles Sunset
Lowracer) are easy to ride, even after I have hammered to the point of
exhaustion on a double metric century.

> Also, heel overlap is not a good idea. Sooner or later it will trip
> you up.
>
Not a big deal as long as there is nothing for the crank to hit. Crank
to wheel overlap can dump you in a hurry. Of course, that can only
happen at low speed, and a low speed fall on a recumbent is trivial
compared to doing the same on an upright.

--
Tom Sherman - Holstein-Friesland Bovinia
The weather is here, wish you were beautiful

[Tom Sherman[_2_]]

Nate Nagel wrote:
> [...] The three major shortcomings
> of drum brakes in general are 1) brakes often undersized for the
> vehicle, exacerbating other problems (not an issue on my car, but, say,
> the 9" front drums on an old Dart are an insult to common sense.)[...]

I drove the early 1970's Plymouth sibling for a bit, and the brakes were
about as effective as using just the hand brake on a proper automobile.
The only thing worse was the steering, which felt like a wheel mounted
to a bearing, with absolutely no feedback. The rest of the car was
hardly better.

No wonder Chrysler would have gone bankrupt without corporate welfare.

--
Tom Sherman - Holstein-Friesland Bovinia
The weather is here, wish you were beautiful

[Tom Sherman[_2_]]

aka Jobst Brandt wrote:
> [...]
> That's why heavy trucks still use drum brakes, drums having large
> surface to reject heat by forced convection. Highways have long dual
> tired skid marks because the response to brake application cannot be
> well controlled with drum brakes.[...]
>
Herr Brandt must not have driven a 2002-2005 Honda Civic, which has rear
drum brakes but exhibits none of the ills that Brandt claims are
inherent to drums.

--
Tom Sherman - Holstein-Friesland Bovinia
The weather is here, wish you were beautiful

[Tom Sherman[_2_]]

aka Jobst Brandt wrote:
> [...]
> OK! You keep making these claims and show no reason or reference for
> them. Just inspect BMW cars and note that even their large "sport
> cars"do not have holes in the disks.[...]

Like these vented rotors for BMW's?
<http://www.global-b2b-network.com/direct/dbimage/10318396/Brake_Rotor_For_BMW_and_BENZ.jpg>

No holes on the braking surface, but radial holes between the surfaces.

--
Tom Sherman - Holstein-Friesland Bovinia
The weather is here, wish you were beautiful

[Tom Sherman[_2_]]

Nate Nagel wrote:
> Clive George wrote:
>> [...]
>> I did have an amusing time recently reading about USian muscle cars -
>> with hundreds of BHP, but engineered for the 1/4 mile rather than
>> actual speed, as could be seen by the gearing they came with. Probably
>> a good thing though given the handling and braking :-)
>
> yeah, some of the larger ones were borderline irresponsible, e.g.
> Hemi-powered midsize MoPars with disc brakes *optional* - a Studebaker
> isn't so bad as it is a fairly light car and their drum brakes were
> better than most. Handling was never a big priority as even most
> "sporty" American cars were really primarily people haulers and long
> distance tourers; if you wanted to go around corners fast you needed to
> look to something European. The Corvette being the only real notable
> mass-market exception that comes to mind...
>
Not mass market by any stretch of the imagination, but a USian car with
a big V-8 that likely gave Signore Ferrari sleepless nights:
<http://www.legendarymotorsport.com/Portals/0/Good.jpg>.

--
Tom Sherman - Holstein-Friesland Bovinia
The weather is here, wish you were beautiful

[Tom Sherman[_2_]]

Clive George wrote:
> "Nate Nagel" > wrote in message
> ...
>
>> This is what I was alluding to when I mentioned the improved pedal
>> feel of drums - the vacuum booster commonly used does make for a far
>> less direct feel on the brake pedal.
>
> You might find driving a power-braked car amusing - on a proper citroen,
> the pedal doesn't move (noticably), but the braking is still
> proportional to how hard you press. Coming from an over-assisted
> conventional car was an interesting reminder of the difference.
>
>> Any modern car equipped with disc brakes. In my driveway, a Chevy
>> Impala (icky company car) a Porsche 944 and a Ford F-150. All have
>> vented discs, at least on the front.
>
> Many over here don't have vented. My CX had them (all round :-) ), but
> nothing else I've owned. The stuff you've just mentioned comes under
> "bigger or faster than normal". Of course with the weight inflation of
> cars, they're getting rather more common...
>
Bigger and faster than normal for the EU, but not for NA.

--
Tom Sherman - Holstein-Friesland Bovinia
The weather is here, wish you were beautiful

[Tom Sherman[_2_]]

Andrew Muzi wrote:
>>> TBerk > wrote:
>>>> Obviously I would assume they could if you clamp down fast enough.
>
>> landotter > wrote:
>>> Yes, if you don't brace yourself and are unfamiliar with the brake and
>>> grab wildly, any powerful brake can be dangerous--but so can many
>>> things in life. Well adjusted brakes should be easy to modulate,
>>> provided you're not inebriated and have practiced a few panic stops,
>>> and shouldn't necessitate the purchase of a new bicycle.
>>> Be careful when posting questions like this, because you may attract
>>> 'bent riders, who are bearded hammers in search of nails--sometimes
>>> with orange flippy flags!
>
> Harry Brogan wrote:
> > I do NOT have orange flippy flags!!!!!! ROFLMAO
>
> Not yet?
> Tom Sherman can probably help you choose a nice flippy orange one.

I suggest a red flag with a gold "hammer & sickle" logo. ;)

--
Tom Sherman - Holstein-Friesland Bovinia
The weather is here, wish you were beautiful

[Tom Sherman[_2_]]

Michael Press wrote:
> In article >,
> Tom Sherman > wrote:
>
>> TBerk ? wrote:
>>> On May 1, 8:31 pm, Tom Sherman >
>>> wrote:
>>>> landotter wrote:
>>> <snippage>
>>>>> Be careful when posting questions like this, because you may attract
>>>>> 'bent riders, who are bearded hammers in search of nails--sometimes
>>>>> with orange flippy flags!
>>>> Since so many upright riders feel necessary to comment on the alleged
>>>> disadvantages of recumbents (often quite rudely in person), it is only
>>>> fair to do the same for uprights.
>>> But yeah, you guys are thread-jacking though.
>>>
>> In other breaking news...
>>
>> Thread drift is a fact of life on Usenet.
>
> Almost all non sequiturs on recumbent bicycles
> are introduced by you.

Dude, [1]

For the record, Mike Schwab first introduced recumbents into this
thread, not me. "DougC" and "landotter" also posted responses mentioning
recumbents independently of anything I posted.

> You walk, or roll supine,
> with `Kick Me' sign and are surprised
> that you are sore? Try going a year without
> a gratuitous introduction of recumbent bicycles
> and see how things work out.
>
I did not bring up the subject in this thread, as a cursory review of
the thread would make blindingly obvious.

Change the charter of rec.bicycles.tech to exclude recumbents, and I
will not mention them without an "OT" lead to the subject line. Until
then, deal with their occasional mention.

[1] Feel free to respond "Don't call me dude".

--
Tom Sherman - Holstein-Friesland Bovinia
The weather is here, wish you were beautiful

[Tom Sherman[_2_]]

TBerk wrote:
> On May 1, 10:17 pm, Tom Sherman >
> wrote:
>> TBerk ? wrote:
> <snip>
>>> But yeah, you guys are thread-jacking though.
>> In other breaking news...
>> Thread drift is a fact of life on Usenet.
>>
>> --
>> Tom Sherman
>
> Sorry, forgot to include an emoticon 8])
>
>
> TBerk
> I'm going to be looking into replacement forks with disk brake
> capacity. Stay tuned everybody...

Be sure to get a system with a through-bolt or one of the rare forks
that has the dropouts and/or caliper mounts arranged so the brake is not
trying to eject the wheel:
<http://www.ne.jp/asahi/julesandjames/home/disk_and_quick_release/index.html>.

--
Tom Sherman - Holstein-Friesland Bovinia
The weather is here, wish you were beautiful

[TBerk]

On May 2, 7:49 pm, Tom Sherman >
wrote:
> TBerk wrote:
> > On May 1, 10:17 pm, Tom Sherman >
> > wrote:
> >> TBerk ? wrote:
> > <snip>
> >>> But yeah, you guys are thread-jacking though.
> >> In other breaking news...
> >> Thread drift is a fact of life on Usenet.
>
> >> --
> >> Tom Sherman
>
> > Sorry, forgot to include an emoticon 8])
>
> > TBerk
> > I'm going to be looking into replacement forks with disk brake
> > capacity. Stay tuned everybody...
>
> Be sure to get a system with a through-bolt or one of the rare forks
> that has the dropouts and/or caliper mounts arranged so the brake is not
> trying to eject the wheel:
> <http://www.ne.jp/asahi/julesandjames/home/disk_and_quick_release/inde...>.
>
> --
> Tom Sherman -


Now, see? While as yet unsubstantiated it seems like the kind of help
I started this thread for in the 1st place.


TBerk

[TBerk]

For somebody who says they worked with ATE you should know what
'vented' means re: a disk brake.

Lets take a little quiz:

- What are vented disks?

- What are cross drilled disks?

- What are slotted disks?


Maybe you'd like to Google ATE Atomic disk for some help.

While youre at it, Google up the standard front brakes for, say, a VW
GTI circa 1984. (ATE being an OEM btw.)

After you have completed your homework you can get out of my thread
please sir.


TBerk
bikes, remember?

[Lou Holtman[_2_]]

Nate Nagel wrote:
> wrote:
>> Nate Nagel wrote:
>>
>>
>>>>>>>>> Lots of cars didn't used to have servo assistance on the
>>>>>>>>> brakes. All the force and work required to brake came from
>>>>>>>>> your leg. And yet you could slow down a tonne of car from
>>>>>>>>> 70mph like that.
>>
>>
>>>>>>>> Drum brakes used massive self servo action to achieve useful
>>>>>>>> braking. Because that effect is highly unpredictable, they had
>>>>>>>> both lock-up and fade. That is why we use disks today. You
>>>>>>>> may recall that this was discussed here at great length.
>>
>>
>>>>>>> I don't understand why you consider that action "highly
>>>>>>> unpredictable" it's simply speed dependent. Sure they lock up
>>>>>>> if you stomp on 'em but so will boosted discs. The fade comes
>>>>>>> from the inability of the shoes and drum to shed heat as
>>>>>>> effectively as discs where all the parts are out in the open and
>>>>>>> in some racing applications even have forced air ducted over
>>>>>>> them for additional cooling.
>>
>>
>>>>>> I think you don't know the history of the drum brake. It's self
>>>>>> servo action is laid out about a specific friction coefficient
>>>>>> such that when it is a bit high, brakes lock up (even after
>>>>>> taking the foot off the pedal)
>>
>>
>>>>> Which is not an issue on any automotive application, as if
>>>>> anything, current non-asbestos linings have an even lower
>>>>> coefficient of friction than the original linings around which the
>>>>> brake system was designed. I have seen some high-performance
>>>>> linings made available for various vintage drum brake setups
>>>>> (presumably for vintage racing) and have not ever heard of this
>>>>> happening in practice.
>>
>>
>>>>>> and when it is a bit low from heating, there is essentially no
>>>>>> brake at all, resulting in run-aways on mountain roads.
>>
>>
>>>> The servo effect is what makes the drum brake respond poorly and
>>>> why, if you read the Wiki article, no RR ever used drum brakes,
>>>> skidding a wheel being a major loss.
>>
>>
>>>>> That much is true. Of course this can also happen with discs, if
>>>>> you abuse them enough, but discs cool down *much* faster than
>>>>> drums given that the friction surface is in direct contact with
>>>>> cooling air, the discs have a higher surface area to mass ratio,
>>>>> and that the calipers and at least portions of the linings are
>>>>> also in closer proximity to cooling air than in a drum brake.
>>
>>
>>>>> It cannot happen with disks. The relation of the friction
>>>>> coefficient and brake retardation is linear so the 5% change in
>>>>> friction that formerly cause total brake failure, the disk sees
>>>>> a 5% change. It's much like boiling engines in cars. That
>>>>> they don't boil today is not because they have better
>>>>> radiators, but because they have a non-leaking water pump seal
>>>>> and don't lose coolant.
>>
>>
>> http://en.wikipedia.org/wiki/Engine_cooling#Why_automobile_engines_were_air-cooled
>>
>>
>>
>>> a 5% change in brake friction will not cause a "total brake failure"
>>> on any decent automotive brake system. Now it may cause more than
>>> 5% loss on a servo-action system, but not "total."
>>
>>
>>>>>>> Old manual drum brakes are actually quite pleasant to drive on,
>>>>>>> so long as you're not racing or driving fast through the
>>>>>>> mountains. IMHO they have a much better pedal feel than all but
>>>>>>> the best new disc brakes; certainly more direct as there is a
>>>>>>> direct hydraulic connection between foot and shoes with only a
>>>>>>> very few, simple mechanical parts in between.
>>
>>
>>>>>> Oh nostalgia for things that weren't. Read:
>>
>>
>> http://en.wikipedia.org/wiki/Brake_fade#Fade_in_drum_brakes
>>
>>
>>>>> Seeing as I actually own and (occasionally) drive a '55 Studebaker
>>>>> coupe equipped with the (excellent) factory equipment brakes, with
>>>>> the only upgrade being the addition of finned drums from a later
>>>>> model car, I can say that they certainly aren't anywhere near the
>>>>> death-dealing devices that you seem to be making them out to be.
>>>>> The three major shortcomings of drum brakes in general are 1)
>>>>> brakes often undersized for the vehicle, exacerbating other
>>>>> problems (not an issue on my car, but, say, the 9" front drums on
>>>>> an old Dart are an insult to common sense.) 2) Cooling - drum
>>>>> brakes do retain heat far more so than do discs, resulting in
>>>>> earlier fading. 3) single circuit master cylinders can result in
>>>>> complete brake system failure with one single hydraulic failure.
>>>>> Not an issue with the drums themselves, but legal until the late
>>>>> 60's and therefore common on most vehicles you'll find with four
>>>>> wheel drum brakes.
>>
>>
>>>> I take it you are saying that the auto companies of the world are
>>>> barking up the wrong tree when they dumped the drum brake. That's
>>>> a bit far fetched. Drum brakes are non-linear and unreliable.
>>
>>
>> http://tinyurl.com/jhiu
>>
>>
>>> No, I'm saying that while discs are definitely an improvement, drums
>>> are not nearly as dangerous and unacceptable, at least in the better
>>> automotive implementations, as you make them out to be.
>>
>>
>>> How do you explain, if the servo-action is responsible for the
>>> effects that you claim, that some automotive drums did *not* use
>>> servo-action brakes and still exhibited similar fade? It's the
>>> heat, plain and simple. That was the biggest downfall of drums, and
>>> it's the biggest advantage of discs. To a lesser extent the
>>> increased linearity of brake torque vs. line pressure that you did
>>> mention. That is not to say that there aren't downsides - the
>>> biggest *disadvantage* of discs is the necessity to install a power
>>> booster on all but the lightest cars, as you need significantly more
>>> line pressure to develop the same brake torque as the same size drum
>>> brake. This is what I was alluding to when I mentioned the improved
>>> pedal feel of drums - the vacuum booster commonly used does make for
>>> a far less direct feel on the brake pedal.
>>
>>
>> When the brake application force is in the direction of drum rotation,
>> as it must be with drum brakes, then there is a self energising
>> effect.
>
> Actually, it doesn't matter which direction, on most brakes. The servo
> effect works both ways, but the leading shoe is smaller for reasons of
> even wear.
>
>> Proof of that is the rum brakes lock up at times when the
>> friction coefficient is slightly higher than the design level.
>
> Ok, so? that's not generally a problem.
>
>> All
>> deum brakes have servo effect.
>
> No, there are most definitely non-servo drum brakes. Early Studebaker
> drums for example, or some of the odd dual wheel cylinder designs.
>
>> If you have worked on drum brakes you
>> should have noticed that they are designated leading shoe brakes, that
>> is that the activating hydraulic piston is pushing in the direction of
>> drum rotation.
>
> And that is for reasons of even shoe wear. also the wheel cylinder
> pushes both ways in the normal drum brake setup, so the servo action can
> work in both directions.
>
>>
>>>>>>>>> The difficult part is getting rid of all the heat that the
>>>>>>>>> brakes are converting the bike's kinetic energy into.
>>
>>
>>>>>> That's why heavy trucks still use drum brakes, drums having large
>>>>>> surface to reject heat by forced convection. Highways have long
>>>>>> dual tired skid marks because the response to brake application
>>>>>> cannot be well controlled with drum brakes.
>>
>>
>>>>> I believe that they still use drums because they're easier to work
>>>>> with in an air brake application. They still don't shed heat
>>>>> nearly as well as to discs. I suspect many of those skid marks
>>>>> are also the result of air system failures, not panic stops gone
>>>>> bad.
>>
>>
>>>> You are guessing. Brakes are used for performance and disks large
>>>> enough to control a large truck will not fit inside standard truck
>>>> wheels. That's why disks are not used there.
>>
>>
>>> I actually *have* seen discs on heavy trucks... not nearly as many
>>> as drums, but they are out there.
>>
>>
>> You may have seen them on tractors of semi trailer rigs, but not on
>> the tandem dual dive axles or the semitrailer where heavy braking
>> occurs.
>>
>>
>>>>>>>> Apparently the bicycle industry is not addressing that part of
>>>>>>>> the problem when the surface area and thermal mass their
>>>>>>>> gossamer rings of steel have. I have asked brake manufacturers
>>>>>>>> why their disks are mostly air with a thin pattern of thin
>>>>>>>> steel between. For cooling is the answer. Maybe they should
>>>>>>>> tell the automotive and railway people about their theory.
>>
>>
>>>>>>> ??? most automotive disc brakes are "vented," that is, the
>>>>>>> braking surfaces are separated by a webbing of cast iron
>>>>>>> intended to have air pass through. High-performance rotors are
>>>>>>> also cross-drilled and/or slotted.
>>
>>
>>>>>> I think you'll find that they are not vented but rather solid
>>>>>> disks with no holes.
>>
>>
>>>>> Not true at all.
>>
>>
>>>> OK! You keep making these claims and show no reason or reference
>>>> for them. Just inspect BMW cars and note that even their large
>>>> "sport cars"do not have holes in the disks.
>>
>>
>>> But they are still vented.
>>
>>
>> Look at all the high performance (BMW, Mercedes, Caddillac, Chrysler,
>> Cheverolet, Buick,...) cars and you will see they have no holes. You
>> must be assuming car companies are taking safety lightly if they sell
>> the largest part of their cars with, as you claim, inferior disks that
>> have no holes.
>
> They may not be cross drilled, but they are all vented.
>
>>>>>> The cross drilling is found only on vehicles tauted to be high
>>>>>> performance while no passenger sedan has cross drilling that has
>>>>>> no technical advantage but is a relic of the days when brake fade
>>>>>> was believed to be caused by out-gassing of brake shoes to
>>>>>> generate a gas bearing. The holes allow that imaginary gas to
>>>>>> escape.
>>
>>
>>>>> True, but all but very light and/or inexpensive cars still use
>>>>> vented rotors, at least on the front. you are confusing
>>>>> cross-drilling and/or slotting with simple venting, which is a
>>>>> common feature of nearly all automotive disc brakes. Look at a
>>>>> disc edge-on, you will see that it is not solid but is essentially
>>>>> two solid braking surfaces connected by a webbing and with lots of
>>>>> air space in between. That is what is commonly known as a
>>>>> "vented" rotor.
>>
>>
>>>> Name a few please.
>>
>>
>>> Any modern car equipped with disc brakes. In my driveway, a Chevy
>>> Impala (icky company car) a Porsche 944 and a Ford F-150. All have
>>> vented discs, at least on the front.
>>
>>
>> Not the new ones aold today. Exactly these are proof that there is no
>> benefit to the cross drillings in the disks of "sports cars".
>
> Yes, all of the new ones sold today. They are vented, as I defined
> above (and as is common usage.)
>
>>
>>> The last car I saw *without* vented front discs was my mom's '86 VW
>>> Golf. It did have solid front discs.
>>
>>
>> You use the term "vemnted" without definition. What do you mean?
>
>
> See above, I defined the common usage of the term when referring to brakes.
>
>>
>>>>>> I worked in brake design with Girling and ATE in the years when
>>>>>> the auto industry was changing to disks and was amazed at the
>>>>>> amount of myth and lore surrounding brakes.
>>
>>
>>>>> I don't mean to be insulting, but that surprises me given the
>>>>> inaccuracies in your post. Although that would explain your
>>>>> unfamiliarity with vented rotors, as AFAIR at least the Studebaker
>>>>> applications of the first Girling brakes did in fact use solid
>>>>> rotors. I would assume that other applications of those brakes
>>>>> did as well as I'm not aware of any significant variations on the
>>>>> caliper design.
>>
>>
>>>> You are not trying hard enough to not be insulting. Your
>>>> unsupported claims are in themselves insulting in facer of evidence
>>>> to the contrary. The subject here was to cross drilling with holed
>>>> through the disk faces. RR disks are all internally radially
>>>> vented in the disk casting.
>>
>>
>> http://www.merriam-webster.com/dictionary/disk
>>
>>
>>> At this point, I can't even determine if you understand the
>>> difference between venting and drilling. If you can't keep your
>>> terminology straight there's no point in continuing this discussion.
>>
>>
>> At this point I suggest you heed your request for definition of disk
>> form. I detect you are trying to make a technical educational course
>> about disk brake, not understanding the basic difference between disks
>> and drums. I am not ready to outline a course on disk brakes here.
>
> I'm afraid I don't need your "technical educational course" - not to do
> the credential dick-waving thing, but I too have worked professionally
> with braking systems (albeit specifically with ABS software) and
> apparently quite a bit more recently than you. You're confusing venting
> with cross-drilling, or you're not understanding the terminology that
> I'm using which is standard and has been since the late 60's.
>
> nate
>


A vented disk is like a rotor of a radial ventilator. Maybe Jobst
understands now what you mean.

Lou

[Ben C]

On 2008-05-02, Nate Nagel > wrote:
[...]
> How do you explain, if the servo-action is responsible for the effects
> that you claim, that some automotive drums did *not* use servo-action
> brakes and still exhibited similar fade? It's the heat, plain and
> simple.

I used to have a car with four drum brakes (still have it actually long
story).

There were three distinct kinds of fade. The first was "pedal drop",
which was easily cured by pumping the pedal a couple of times. I believe
this was most likely to be caused by drum expansion. But I'd be
interested to hear other theories.

The second was fluid fade, where the fluid boils, resulting in a
distinctive "spongy" feel to the pedal. That was cured by changing the
brake fluid: modern fluid in good condition seemed more than capable of
surviving the highest temperatures that could be produced by such a
braking system.

The third kind was when you had the pedal pumped up, the fluid wasn't
boiling, but you'd find yourself pushing very hard on the pedal without
the car slowing down nearly as much as you were hoping. It didn't go
spongy or drop, just didn't seem to do much.

I took it that was some kind of reduction of friction coefficient caused
by too much heat, but don't claim to be able to explain it completely.

> That was the biggest downfall of drums, and it's the biggest advantage
> of discs. To a lesser extent the increased linearity of brake torque
> vs. line pressure that you did mention. That is not to say that there
> aren't downsides - the biggest *disadvantage* of discs is the
> necessity to install a power booster on all but the lightest cars, as
> you need significantly more line pressure to develop the same brake
> torque as the same size drum brake. This is what I was alluding to
> when I mentioned the improved pedal feel of drums - the vacuum booster
> commonly used does make for a far less direct feel on the brake pedal.

Another downside of drums was that if you had to brake suddenly there
was a greater chance of the brake snatching on on one side before the
other.

This I took to be because they aren't "self-adjusting" in the simple way
disks are, so the pads on each side are likely to start off a more
variable distance from their target, and because of the leading-shoe
servo action which makes them snatch on as soon as they make contact.

Mine weren't self-adjusting at all, you had to keep adjusting them. Some
other cars had self adjusting mechanisms of various kinds but they
weren't as simple as the way a disk caliper works because they need
springs to retract the pads.

I don't miss drum brakes at all.

[...]
>> OK! You keep making these claims and show no reason or reference for
>> them. Just inspect BMW cars and note that even their large "sport
>> cars"do not have holes in the disks.
>>
>
> But they are still vented.

I also haven't seen a disk that wasn't vented in the way you described
for years. Cross-drilled disks are rarer. You see them on Porsche 911s.

[Ben C]

On 2008-05-03, Nate Nagel > wrote:
> wrote:
[...]
>> All
>> deum brakes have servo effect.
>
> No, there are most definitely non-servo drum brakes. Early Studebaker
> drums for example, or some of the odd dual wheel cylinder designs.

Just to clarify he means the servo effect of leading shoes, not of a
manifold vacuum operated brake servo or "power booster".

>> If you have worked on drum brakes you should have noticed that they
>> are designated leading shoe brakes, that is that the activating
>> hydraulic piston is pushing in the direction of drum rotation.
>
> And that is for reasons of even shoe wear.

No Jobst is right about that: it is for the servo action.

> also the wheel cylinder pushes both ways in the normal drum brake
> setup, so the servo action can work in both directions.

Front drums usually have two cylinders because they're twin leading-shoe
for best braking going forwards.

Rear drums often have one cylinder with a piston coming out of each end
to give you one leading and one trailing shoe. That's so you have some
braking in reverse. Also because you might park facing up a hill.

[Ben C]

On 2008-05-03, Tom Sherman > wrote:
> aka Jobst Brandt wrote:
>> [...]
>> That's why heavy trucks still use drum brakes, drums having large
>> surface to reject heat by forced convection. Highways have long dual
>> tired skid marks because the response to brake application cannot be
>> well controlled with drum brakes.[...]
>>
> Herr Brandt must not have driven a 2002-2005 Honda Civic, which has rear
> drum brakes but exhibits none of the ills that Brandt claims are
> inherent to drums.

Drums are fine on the back. The back brakes do very little in normal
driving, and are mostly useful for when you're parked, for which the
drum is a good design as it shrinks "on" when it cools.

You don't want drums on the front.

A cable operated parking brake on rear disks is possible but you usually
get a self-adjusting threaded oddity in the rear slave cylinders which
is a bugger when you come to change the pads because you have to twist
it back in.

Some cars with rear disks have little drums as well, just for the
parking brake.

[Ben C]

On 2008-05-03, TBerk > wrote:
> On May 2, 7:49 pm, Tom Sherman >
[...]
>> Be sure to get a system with a through-bolt or one of the rare forks
>> that has the dropouts and/or caliper mounts arranged so the brake is not
>> trying to eject the wheel:
>> <http://www.ne.jp/asahi/julesandjames/home/disk_and_quick_release/inde...>.
>>
>> --
>> Tom Sherman -
>
>
> Now, see? While as yet unsubstantiated it seems like the kind of help
> I started this thread for in the 1st place.

The wheel ejection problem is correct in theory but in practice it
doesn't happen if you do your QRs up reasonably tight.

[Nate Nagel[_2_]]

Ben C wrote:
> On 2008-05-03, Nate Nagel > wrote:
>
wrote:
>
> [...]
>
>>>All
>>>deum brakes have servo effect.
>>
>>No, there are most definitely non-servo drum brakes. Early Studebaker
>>drums for example, or some of the odd dual wheel cylinder designs.
>
>
> Just to clarify he means the servo effect of leading shoes, not of a
> manifold vacuum operated brake servo or "power booster".

I understand that. There are drum brakes that were put into production
that did *not* use the typical servo-action design.

nate

--
replace "roosters" with "cox" to reply.
http://members.cox.net/njnagel

[Tom Sherman[_2_]]

Ben C wrote:
> On 2008-05-03, TBerk > wrote:
>> On May 2, 7:49 pm, Tom Sherman >
> [...]
>>> Be sure to get a system with a through-bolt or one of the rare forks
>>> that has the dropouts and/or caliper mounts arranged so the brake is not
>>> trying to eject the wheel:
>>> <http://www.ne.jp/asahi/julesandjames/home/disk_and_quick_release/inde...>.
>>>
>>> --
>>> Tom Sherman -
>>
>> Now, see? While as yet unsubstantiated it seems like the kind of help
>> I started this thread for in the 1st place.
>
> The wheel ejection problem is correct in theory but in practice it
> doesn't happen if you do your QRs up reasonably tight.

If there is any motion between the axle and the dropout, this could
cause the QR to loosen. In addition, the skewer could fail or the QR
could be loosened by a minor impact while riding off-road.

While wheel ejection is obviously a rare occurrence, considering the
likely severity of the accident if wheel ejection does occur, NOT
designing the wheel retention system to eliminate the possibility is
irresponsible.

--
Tom Sherman - Holstein-Friesland Bovinia
The weather is here, wish you were beautiful

[Michael Press]

In article >,
Ben C > wrote:

> On 2008-05-03, TBerk > wrote:
> > On May 2, 7:49 pm, Tom Sherman >
> [...]
> >> Be sure to get a system with a through-bolt or one of the rare forks
> >> that has the dropouts and/or caliper mounts arranged so the brake is not
> >> trying to eject the wheel:
> >> <http://www.ne.jp/asahi/julesandjames/home/disk_and_quick_release/inde...>.
> >
> > Now, see? While as yet unsubstantiated it seems like the kind of help
> > I started this thread for in the 1st place.
>
> The wheel ejection problem is correct in theory but in practice it
> doesn't happen if you do your QRs up reasonably tight.

Depend on what you mean by ejection. Many riders reported
a loose quick release at the bottom of the hill that was
tight at the top. Braking reaction force in the direction
of the open fork tip combined with the short, hard forces
of a fast, steep down hill run combine to loosen the
quick release nut.

--
Michael Press

[Peter Cole[_2_]]

Ben C wrote:

>>> OK! You keep making these claims and show no reason or reference for
>>> them. Just inspect BMW cars and note that even their large "sport
>>> cars"do not have holes in the disks.
>>>
>> But they are still vented.
>
> I also haven't seen a disk that wasn't vented in the way you described
> for years. Cross-drilled disks are rarer. You see them on Porsche 911s.

Cross-drilled seems to be more about looks than anything else. "Vented"
or "ventilated" rotors are another matter. They appear to be reasonably
effective, but it's not a *huge* effect (+40%, rather than 100%).

The best paper I have found:
http://adt.lib.rmit.edu.au/adt/uploads/approved/adt-VIT20070108.121737/public/02whole.pdf

Conclusions: The most important thing is air flow to the brake area
(open wheels, etc.), second importance is vehicle speed, third is rotor
venting (radial), etc.

I had thought one of the reasons that "vented" rotors were used was to
make the disk stiffer in the face of thermal distortion, but it's not
clear that is the case. I doubt that they cost much more to make, so
with a significant improvement in dissipation, it's probably a
no-brainer. Outside of the track, it seems like modern front wheel
disks, vented or not, seem to have plenty of capacity, so I don't know
what the big deal is. That's all I've driven for the past 30 years.

[JG]

My physics-fu is feeling a little weak.

While it is true that the limits on grip strength and size will limit
how much force you can put into the brake pads, it does seem that
that force on the pads at a 28" rim is going to be four times as
effective as pads on a 7" rotor, and that a disk brake will be
inherently less effective than a rim brake. Or am I missing
something?

JG

[Tom Sherman[_2_]]

JG wrote:
> My physics-fu is feeling a little weak.
>
> While it is true that the limits on grip strength and size will limit
> how much force you can put into the brake pads, it does seem that
> that force on the pads at a 28" rim is going to be four times as
> effective as pads on a 7" rotor, and that a disk brake will be
> inherently less effective than a rim brake. Or am I missing
> something?
>
Different materials are in contact with each other during braking in
each case.

Rim brakes are fair to poor in the wet, and lousy in mud and snow.

--
Tom Sherman - Holstein-Friesland Bovinia
The weather is here, wish you were beautiful

[A Muzi]

JG wrote:
> My physics-fu is feeling a little weak.
>
> While it is true that the limits on grip strength and size will limit
> how much force you can put into the brake pads, it does seem that
> that force on the pads at a 28" rim is going to be four times as
> effective as pads on a 7" rotor, and that a disk brake will be
> inherently less effective than a rim brake. Or am I missing
> something?

All else being equal, yes. But all else is not equal. Watch you calipers
flex during braking for example. And try to put a pothole rim dent on a
stainless disc for another. And so on.

They are different but IMHO neither is 'better'.
--
Andrew Muzi
<www.yellowjersey.org/>
Open every day since 1 April, 1971
** Posted from http://www.teranews.com **

[Andre Jute[_2_]]

On May 3, 10:42*pm, JG > wrote:
> My physics-fu is feeling a little weak.

Braking is limited by the coefficient of friction between the road and
the tire. Theoretically, at least, there is no intrinsic reason for
any of the brake methods (rim, disc, drum) to be inferior to the
others. In practice the mechanics of bikes are so well developed that
any adult or child can apply enough braking force to exceed the
friction between tire and road, regardless of the type of brake
fitted. Under ideal conditions, which is what theory deals in, all
bicycle brakes are better than good enough and therefore equal.

> While it is true that the limits on grip strength and size will limit
> how much force you can put into the brake pads, *it does seem that
> that force on the pads at a 28" rim is going to be four times as
> effective as pads on a 7" rotor, and that a disk brake will be
> inherently less effective than a rim brake. *Or am I missing
> something?

If only practice could be as simple as theory! (Why, my perpetual
motion machine might suddenly burst into a couple of Hallelujah
choruses...) But, for a start, the available friction against the rim
is limited by rain, snow and just plain dirt, which is not true of
discs and roller brakes. Since the weather is known to be changeable,
that's a major functional inequality already. Also, as Andrew has
pointed out, rims are more vulnerable to becoming uneven than the
competing types of brakes, further detracting from the ideal.

It is good to think about these things. I wonder every time I see a
rear disc brake on a bike what it is *for*.

Someone kindly explain "fu" to me. TIA.

Andre Jute
--
http://members.lycos.co.uk/fiultra/BICYCLE%20%26%20CYCLING.html

[Clive George]

"JG" > wrote in message
...
> My physics-fu is feeling a little weak.
>
> While it is true that the limits on grip strength and size will limit
> how much force you can put into the brake pads, it does seem that
> that force on the pads at a 28" rim is going to be four times as
> effective as pads on a 7" rotor, and that a disk brake will be
> inherently less effective than a rim brake. Or am I missing
> something?

That bit is entirely true. However the material for the disk rotor and pads
can be chosen for friction, not weight, the rotor can be kept true more
easily so the pad to rotor distance can be smaller, and caliper can be a lot
smaller so stiffer.
This means the mechanical advantage of the disc brake (movement of lever vs
movement of pad) can be a lot higher on a disk brake, thus making up for the
diameter-related disadvantage.

cheers,
clive

[Clive George]

"Andre Jute" > wrote in message
...

> It is good to think about these things. I wonder every time I see a
> rear disc brake on a bike what it is *for*.

Apart from the obvious "slowing the bike down"?

Not wearing out the rim.
Not overheating the rim while going slowly down steep hills.
Improved mud clearance.
(Not weighing as much as a drum brake)

Those are the big reasons for the rear disc I've got. Of course there is the
other minor point on that bike that the rear brake does actually do quite a
lot.

clive

[Nate Nagel[_2_]]

JG wrote:
> My physics-fu is feeling a little weak.
>
> While it is true that the limits on grip strength and size will limit
> how much force you can put into the brake pads, it does seem that
> that force on the pads at a 28" rim is going to be four times as
> effective as pads on a 7" rotor, and that a disk brake will be
> inherently less effective than a rim brake. Or am I missing
> something?
>
> JG

I'm ASSuming that the disc pucks float much closer to the disc than the
rim brake pads do to the rim, so you can get more mechanical advantage
with the discs without bottoming out the levers.

NB: I know far, far more about car brakes than I do about bicycle discs,
never even having looked closely at one, so I'm just throwing a WAG out
there.

nate

--
replace "roosters" with "cox" to reply.
http://members.cox.net/njnagel

[Tom Sherman[_2_]]

Andre Jute wrote:
> [..]
> It is good to think about these things. I wonder every time I see a
> rear disc brake on a bike what it is *for*.[...]

Mud clearance on an ATB.

Useful braking on a recumbent with rearward weight distribution.

Prevention of rim erosion on any bike ridden in wet weather.

--
Tom Sherman - Holstein-Friesland Bovinia
The weather is here, wish you were beautiful

[[email protected]]

On May 3, 8:44 pm, Nate Nagel > wrote:
>
> I'm ASSuming that the disc pucks float much closer to the disc than the
> rim brake pads do to the rim, so you can get more mechanical advantage
> with the discs without bottoming out the levers.

That's true. In fact, the disk brake bikes I've ridden seemed to have
a small, constant amount of scraping of the brake pad against the
disk. I don't know that it slowed me down, since the bikes were
rather slow hybrids, anyway. But the slight noise is something I
wouldn't accept from my caliper brakes.

- Frank Krygowski

[Ben C]

On 2008-05-04, > wrote:
> On May 3, 8:44 pm, Nate Nagel > wrote:
>>
>> I'm ASSuming that the disc pucks float much closer to the disc than the
>> rim brake pads do to the rim, so you can get more mechanical advantage
>> with the discs without bottoming out the levers.
>
> That's true. In fact, the disk brake bikes I've ridden seemed to have
> a small, constant amount of scraping of the brake pad against the
> disk. I don't know that it slowed me down, since the bikes were
> rather slow hybrids, anyway. But the slight noise is something I
> wouldn't accept from my caliper brakes.

Car disks are the same-- if the disk is flat and perpendicular to the
axle as it should be the pads stay in light contact with the disk the
whole time. There isn't any kind of spring to pull them away. But since
there's no force being applied it causes very little drag. It's a good
design because you don't get any dead travel before the brakes come on.

I think I would also find it a bit annoying on a bike.

[Ben C]

On 2008-05-03, Andre Jute > wrote:
> On May 3, 10:42*pm, JG > wrote:
>> My physics-fu is feeling a little weak.
>
> Braking is limited by the coefficient of friction between the road and
> the tire. Theoretically, at least, there is no intrinsic reason for
> any of the brake methods (rim, disc, drum) to be inferior to the
> others. In practice the mechanics of bikes are so well developed that
> any adult or child can apply enough braking force to exceed the
> friction between tire and road, regardless of the type of brake
> fitted. Under ideal conditions, which is what theory deals in, all
> bicycle brakes are better than good enough and therefore equal.

Just being able to lock wheels doesn't mean the brakes are good enough.
They might overheat if you keep them on for a while going down a hill,
or, in a car, brake hard 10 or 20 times between tight corners without
long enough straights in between for them to cool down.

Once they overheat you get brake fade of various kinds as discussed and
on bicycle rim brakes you might get the tyre blowing off.

[...]
> It is good to think about these things. I wonder every time I see a
> rear disc brake on a bike what it is *for*.

Just to match the front disk brake.

[Mike]

In article >, Harry Brogan <hbrogan57_AT_NOSPAM_DOT_YAHOO_DOT_COM> says...
> On Thu, 1 May 2008 11:21:35 -0700 (PDT), landotter
> > wrote:
>
> >On May 1, 12:51 pm, Harry Brogan
> ><hbrogan57_AT_NOSPAM_DOT_YAHOO_DOT_COM> wrote:
> >> On Thu, 1 May 2008 06:47:38 -0700 (PDT), landotter
> >>
> >> > wrote:
> >> >On Apr 30, 10:49 pm, TBerk > wrote:
> >> >> Obviously I would assume they could if you clamp down fast enough.
> >>
> >> >Yes, if you don't brace yourself and are unfamiliar with the brake and
> >> >grab wildly, any powerful brake can be dangerous--but so can many
> >> >things in life. Well adjusted brakes should be easy to modulate,
> >> >provided you're not inebriated and have practiced a few panic stops,
> >> >and shouldn't necessitate the purchase of a new bicycle.
> >>
> >> >Be careful when posting questions like this, because you may attract
> >> >'bent riders, who are bearded hammers in search of nails--sometimes
> >> >with orange flippy flags!
> >>
> >> I do NOT have orange flippy flags!
> >
> >Yellow?
>
>
> FUNNY!!!!......No....not yellow either.....Here's a photo....
>
> http://i255.photobucket.com/albums/hh160/1957trike/The%20Rig/1000Miles_01012003_02.jpg
>
Odd thing is that teh 'recumbent beard' has risen up from the chin to just below the nose...

Mike

[TBerk]

This has gotten to be a long thread so let me recap a bit:

- The rim has a 'bubble' bend in it, presumably from a hard hit aginst
a sharp edge, pothole, something.

- I _was_ doing a quick stop manuver on purpouse, but of coure I
hadn't counted on the deformation of the rim which led to an
equivelent 'stick in the rim' action.

- Unrelated to the rim dents, this used bike (found stripped and
abandoned in a field) which I found and rebuilt with what I later
discovered was a set of bent forks. That part is on me to have not
really noticed until the paint began to flake off.

- Hence my interest in new forks which opens up an opportunity to
'upgrade' to a disk brake set up.

Meanwhile we have gotten some thread drift, some 'personalities', and
some actually useful info. Typical Usenet.

The frame itself, (with the rack and seat post with a shock in it),
are pretty decent. Of course the front derailer needs a new shifter;
it's broken (I dislike twist shifters) but over all the thing gets the
job done.

To get a new bike (one I'd feel OK about buying new) means spending
fix'r-up'r car money so I'll give this one another level of rebuild
and save my pennies for now.


Dems me thinks.
TBerk

[Werehatrack]

On Wed, 30 Apr 2008 20:49:12 -0700 (PDT), TBerk
> may have said:

>
>Obviously I would assume they could if you clamp down fast enough.

Bloody unlikely.

>I ask because I bruised some rib bones this week when I stomped the
>front brake and *surprise* I found out later my front rim has a bubble
>bend in it from (I guess) a pot hole at some recent time.
>
>Made for a portion of the rim that just wasn't going to get past the
>brake pads, not while I was trying to actually use said brakes.
>
>It would seem a better setup would be one unaffected by a slightly
>bent rim, or so I wonder.

While this is one of the minor advantages of keeping the braking
surface separate from the rim, it's seldom enough of a factor to
justify the added complexity. Good rim brakes at nearly any level
will produce more grab than typical OEM-supplied disc brakes on
low-end and midrange bikes anyway. To toss the rider over the bars,
the wheel must instantaneously cease motion relative to the fork
without breaking traction or bending the fork, which is seldom going
to occur with *any* brake system. I had it happen to me with a stick
jam through the spokes of the front wheel on an ancient
fender-equipped bike decades ago, when I was a lot lighter, but
generally an unexpectedly high braking effort is just going to throw
the rider off the seat and forward against the bars. To go over them,
there needs to be a couple of other factors present.

>TBerk
>it would have been funny if it hadn't hurt so much at the time

BTDT.

--
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