Why do some forks and frames have brake rotor size limits?

wrote:
On Friday, October 27, 2017 at 8:54:45 PM UTC-7, Ralph Barone wrote:
John B. wrote:
On Sat, 28 Oct 2017 01:13:54 +0000 (UTC), Ralph Barone
wrote:

John B. wrote:
On Fri, 27 Oct 2017 09:32:04 -0700, Joerg
wrote:

On 2017-10-27 09:25, Frank Krygowski wrote:
On 10/27/2017 9:58 AM, Joerg wrote:

Finally after many decades the bicycle industry woke up and adopted
what the automotive guys had all along, disc brakes. Why should I
accept an inferior brake system on a new bike when there is a much
better one?

sigh There are advantages and disadvantages to this equipment choice,
just as with other equipment choices. The disadvantages of discs have
been discussed. If they don't matter or apply to you, fine; but they
matter to others.


Many others just don't know any better. I have witnessed several people
riding a bike with hydraulic disc brakes for the first time and the
reaction was usually "WHOA!". Same with me, it almost sent me over the bar.


But I'll note that you're currently in a project to increase your disc's
diameter from something like 160mm or 180mm up to 200mm or more. You
seem to feel bigger diameter is better.


Because bigger is better here.


Well, even "better," why not go up to roughly 622mm? That's what lots
of us prefer, with cable actuation.


The disadvantages have been discussed ad nauseam. A rim brake is not a
disc brake. Not even close.

Care to explain the mechanical difference? I mean a rotating surface
and two friction pads that are tightened against it....
--
Cheers,

John B.

As far as I can tell, the differences between a rim brake and a 622 mm disk
a

1) The disk doesn't have to provide tire clearance, so the pads can sit
closer, facilitating higher mechanical advantage.

I'm not sure that is correct. After all some old Greek guy was
supposed to have said, "Give me a lever and a place to stand and I
will move the earth". Nothing about being close.

No. I'm pretty certain I'm right here. Let's say that you can pull 100 lbs
on your brake lever and the lever has 2" of play before it hits your bars.
You can fiddle with leverage many places in the system, but the product of
that initial 100 lbs and 2" will be constant in the system. If the final
travel of the brake pads is 1/2", then you can apply 400 lbs force to the
pads. If you tighten up your tolerances such that the pads only have to
move 1/16", then you can increase the leverage to the point where you can
apply 3200 lbs force to the pads. In disk brake systems this reduction in
pad-disk distance allow the MA to be increased to compensate for the
decreased leverage of the disk on the wheel. The increases brake pad
pressure at a given bike deceleration is what gives disk brakes more
consistent performance in the wet.

But the leverage includes the respective diameters of the wheel and disk
which actually reduces the STOPPING power of the wheel and also puts a
hell of a lot more strain on the spokes.


Yes, I said that. "allows the MA to be increased to compensate for the
decreased leverage of the disk on the wheel." The increased
pressure/friction at the disk is reduced at the wheel by the ratio of the
wheel to the disk. However, at a given bicycle deceleration (which is what
counts), a disk brake system will have a higher pad pressure that a rim
brake. That will give the disk brake more consistent performance in the
wet (I fixed my typo above).

On Friday, October 27, 2017 at 11:19:12 PM UTC-7, Ralph Barone wrote:
Frank Krygowski wrote:
On Friday, October 27, 2017 at 11:54:45 PM UTC-4, Ralph Barone wrote:
John B. wrote:
On Sat, 28 Oct 2017 01:13:54 +0000 (UTC), Ralph Barone
wrote:

John B. wrote:
On Fri, 27 Oct 2017 09:32:04 -0700, Joerg
wrote:

On 2017-10-27 09:25, Frank Krygowski wrote:
On 10/27/2017 9:58 AM, Joerg wrote:

Finally after many decades the bicycle industry woke up and adopted
what the automotive guys had all along, disc brakes. Why should I
accept an inferior brake system on a new bike when there is a much
better one?

sigh There are advantages and disadvantages to this equipment choice,
just as with other equipment choices. The disadvantages of discs have
been discussed. If they don't matter or apply to you, fine; but they
matter to others.


Many others just don't know any better. I have witnessed several people
riding a bike with hydraulic disc brakes for the first time and the
reaction was usually "WHOA!". Same with me, it almost sent me over the bar.


But I'll note that you're currently in a project to increase your disc's
diameter from something like 160mm or 180mm up to 200mm or more. You
seem to feel bigger diameter is better.


Because bigger is better here.


Well, even "better," why not go up to roughly 622mm? That's what lots
of us prefer, with cable actuation.


The disadvantages have been discussed ad nauseam. A rim brake is not a
disc brake. Not even close.

Care to explain the mechanical difference? I mean a rotating surface
and two friction pads that are tightened against it....
--
Cheers,

John B.

As far as I can tell, the differences between a rim brake and a 622 mm disk
a

1) The disk doesn't have to provide tire clearance, so the pads can sit
closer, facilitating higher mechanical advantage.

I'm not sure that is correct. After all some old Greek guy was
supposed to have said, "Give me a lever and a place to stand and I
will move the earth". Nothing about being close.

No. I'm pretty certain I'm right here. Let's say that you can pull 100 lbs
on your brake lever and the lever has 2" of play before it hits your bars.
You can fiddle with leverage many places in the system, but the product of
that initial 100 lbs and 2" will be constant in the system. If the final
travel of the brake pads is 1/2", then you can apply 400 lbs force to the
pads. If you tighten up your tolerances such that the pads only have to
move 1/16", then you can increase the leverage to the point where you can
apply 3200 lbs force to the pads. In disk brake systems this reduction in
pad-disk distance allow the MA to be increased to compensate for the
decreased leverage of the disk on the wheel. The increases brake pad
pressure at a given bike deceleration is what gives disk brakes misread
consistent performance in the wet.

2) The disk is not connected to the rim, so it doesn't bend and warp when
you hit a pothole. Again, the pads can sit closer and have higher MA.

3) The disk doesn't thermally couple to the tire, so no blowouts on long
descents.

4) The disk is solid, so there's less flexing when you squeeze it with the
pads.

I won't quarrel with Ralph's list of disc advantages. My main points are these:
One can also come up with a list of advantages for caliper brakes; and most
cyclists have no real need of most of the disc advantages. For them, as
throughout bicycling's history, caliper brakes are fine.

That last point is often lost on disc promoters - as in "If they are better,
why not use them?" all the way up to "I'd never buy another bike without disc
brakes."

Just for fun, here's a report on disc brakes compared to other types in an
extreme situation: mountain descents on tandems.

https://tandemgeek.wordpress.com/201...if-you-prefer/

- Frank Krygowski

To be frank Frank, I wasn't trying to make the case for disks being better
than rim brakes, only trying to answer the question "what would the
difference be between a rim brake and a 622 mm disk brake?"

However, if you'd like me to give equal time to the rim brake camp...

1) Disk brakes require an additional component (the disk), while the rim
has to be there anyway.

2) Tighter clearances on disk brakes can mean persnickety adjustments and
weird noises when things aren't perfectly aligned.

3) Disk brakes (but not 622 mm disks) apply more torque to the fork and
they apply it asymmetrically, while rim brakes apply a lower torque, in a
balanced manner, to a stronger part of the fork.

3a) Rim brakes apply force to the rim at right angles to the dropouts, so
there is much less likelihood of wheel ejection.

4) Rim brakes have greater thermal mass (but a lower maximum temperature).

And I'm sure there are another handful of arguments on both sides.

1) They also require special hubs and much stronger spokes. The hubs require larger diameter axles which in turn require redesigned forks.

Under heavy braking on a street bike not specifically designed for disks from the ground up you can see the results of distortion of the forks via the need to constantly correct your path.

I will say that I would have a great deal more faith in the strength of carbon forks for disk bikes that are used with rim brakes.

On Friday, October 27, 2017 at 11:24:01 PM UTC-7, Ralph Barone wrote:
John B. wrote:
On Sat, 28 Oct 2017 03:54:43 +0000 (UTC), Ralph Barone
wrote:

John B. wrote:
On Sat, 28 Oct 2017 01:13:54 +0000 (UTC), Ralph Barone
wrote:

John B. wrote:
On Fri, 27 Oct 2017 09:32:04 -0700, Joerg
wrote:

On 2017-10-27 09:25, Frank Krygowski wrote:
On 10/27/2017 9:58 AM, Joerg wrote:

Finally after many decades the bicycle industry woke up and adopted
what the automotive guys had all along, disc brakes. Why should I
accept an inferior brake system on a new bike when there is a much
better one?

sigh There are advantages and disadvantages to this equipment choice,
just as with other equipment choices. The disadvantages of discs have
been discussed. If they don't matter or apply to you, fine; but they
matter to others.


Many others just don't know any better. I have witnessed several people
riding a bike with hydraulic disc brakes for the first time and the
reaction was usually "WHOA!". Same with me, it almost sent me over the bar.


But I'll note that you're currently in a project to increase your disc's
diameter from something like 160mm or 180mm up to 200mm or more. You
seem to feel bigger diameter is better.


Because bigger is better here.


Well, even "better," why not go up to roughly 622mm? That's what lots
of us prefer, with cable actuation.


The disadvantages have been discussed ad nauseam. A rim brake is not a
disc brake. Not even close.

Care to explain the mechanical difference? I mean a rotating surface
and two friction pads that are tightened against it....
--
Cheers,

John B.

As far as I can tell, the differences between a rim brake and a 622 mm disk
a

1) The disk doesn't have to provide tire clearance, so the pads can sit
closer, facilitating higher mechanical advantage.

I'm not sure that is correct. After all some old Greek guy was
supposed to have said, "Give me a lever and a place to stand and I
will move the earth". Nothing about being close.

No. I'm pretty certain I'm right here. Let's say that you can pull 100 lbs
on your brake lever and the lever has 2" of play before it hits your bars.
You can fiddle with leverage many places in the system, but the product of
that initial 100 lbs and 2" will be constant in the system. If the final
travel of the brake pads is 1/2", then you can apply 400 lbs force to the
pads. If you tighten up your tolerances such that the pads only have to
move 1/16", then you can increase the leverage to the point where you can
apply 3200 lbs force to the pads. In disk brake systems this reduction in
pad-disk distance allow the MA to be increased to compensate for the
decreased leverage of the disk on the wheel. The increases brake pad
pressure at a given bike deceleration is what gives disk brakes more
consistent performance in the wet.

Movement of the parts doesn't make any difference the efficiency is
the pressure applied to the brake lever versus the pressure applied to
the braking device, usually the pads themselves.

A lever that is 1 foot long and moves, lets say, one quarter of the
diameter of a 2 foot circle applies the same force to a load located 1
foot from the fulcrum as a 100 ft lever which moves 1/4 of the
diameter of a 200 ft circle applies to a load that is 100 ft. from the
fulcrum. The first lever moves 19 inches and the second moves 157
feet.

Sure. But the distance you can move your brake lever is limited by the
length of your fingers, and so the distance you can move at the lever end
is essentially fixed. To increase the mechanical advantage in THAT system,
you have to reduce the distance the brake pads move. No ifs, ands, buts or
maybes.

This is only in linear systems. The new Skeleton Campy brakes open further and the brakes close to perhaps 3/32nds from the rim. This gives you immense leverage. They really are quite amazing.

On 2017-10-29 09:15, wrote:
On Friday, October 27, 2017 at 8:17:45 PM UTC-7, Joy Beeson wrote:
On Fri, 27 Oct 2017 06:59:56 -0700, Joerg
wrote:

Oh yeah, now we have to wash out bikes after each rain ride. Standing
out there in the rain with sponge and shampoo. Great.

You don't have a garden hose?

Back when I could ride after the outside faucets had been turned off
for the winter, I used to hose salt and ice off my bike by filling my
water bottles with hot tap water, reserving the first squirt from each
bottle to get under the fenders. I don't think I ever had to make
more than two trips into the house for more water.

Come to think of it, I don't think I ever hosed it in the summer
(except when cleaning the braking surfaces, of course), because I rode
only on pavement. There was one mile of gravel road in an adjacent
county, but the grader wore out and it was cheaper to pave the road
than to buy a new grader.

Yes Joy, but you're a lady and ladies are neat. Except for my wife, the hoarder.


I can't even count how often my wife let off comments such as "But you
sure won't park the bike INSIDE the garage like THIS?!". Or admonished
me that another dirt clump dried, fell off and pulverized in all
directions on the garage floor. So now I have a broom parked next to the
bikes.

The weather forecaster said that I will receive a free bike wash next
weekend.

--
Regards, Joerg

http://www.analogconsultants.com/

On Saturday, October 28, 2017 at 8:09:18 AM UTC-7, Joerg wrote:

And grandpa has driven his cars without safety belts yet survived ...

For people who do not shy away from unpaved roads or use a lot of
singletrack and ride in the rain there is a much more extreme issue: Wet
mud.

There is NO brake the is proof against wet mud. In fact it is perhaps worse on a disk since the additional pressure of the pads can turn the silicon present in most muds into cutting instruments that on rim brakes cuts into the rubber show rather than the hard and thin disk pad.

On Saturday, October 28, 2017 at 12:08:44 PM UTC-7, Sir Ridesalot wrote:
On Saturday, October 28, 2017 at 11:09:18 AM UTC-4, Joerg wrote:
On 2017-10-27 17:11, John B. wrote:
On Fri, 27 Oct 2017 06:58:27 -0700, Joerg
wrote:

On 2017-10-27 01:11, John B. wrote:
On Wed, 25 Oct 2017 07:53:11 -0700, Joerg
wrote:

On 2017-10-24 17:21, John B. wrote:
On Tue, 24 Oct 2017 11:47:12 -0700, Joerg
wrote:

On 2017-10-24 07:27, wrote:
On Tuesday, October 24, 2017 at 2:19:48 AM UTC-7, John B. wrote:
On Mon, 23 Oct 2017 10:09:20 -0700, Jeff Liebermann
wrote:

On Mon, 23 Oct 2017 12:48:29 +0700, John B.
wrote:

On Sun, 22 Oct 2017 20:51:15 -0700, Jeff Liebermann
wrote:

On Mon, 23 Oct 2017 07:02:08 +0700, John B.
wrote:

But re disc brake cooling F1 car brakes appear to work with
the discs red hot. In the 1,000 degree (F) range. And they
use Carbon Fiber discs too :-) And everyone knows that CF
is better.

"Thermal Conductivity of Carbon Fiber, and other Carbon
Based Materials"
http://www.christinedemerchant.com/carbon_characteristics_heat_conductivity.html


"So...Is Carbon Fiber a good heat conductor?
As usual the answer is "it depends." The short answer is NO
not when regular carbon fiber is made up in regular epoxy and
expected to conduct heat across the thickness. IF a highly
carbonized pan fiber with graphite or diamond added, is
measured for heat transmission in the length of the fiber it
is very good and can rival and exceed copper."

On the other hand, they seem to work pretty well :-) See
https://www.youtube.com/watch?v=h5JcHAEmIYM for a visual
indication of heat dissipation. :-)

Impressive. I'll assume it's a carbon-carbon rotor, since all F1
cars seem to using them.

Undoubtedly so. But if the advantage of "carbon" bikes can be
extolled that a carbon-carbon frame must have twice the bragging
rights :-)


http://www.racecar-engineering.com/technology-explained/f1-2014-explained-brake-systems/


(4 pages)
"A typical road car uses a cast iron brake disc with an organic
brake pad. In an F1 car, though, the same material is used for
both disc and pad, and this material is known as carbon-carbon -
a significantly different material to the carbon-fibre
composites used in the rest of the car" In other words, the F1
brakes are NOT made from CF.

Some detail on Formula 1 brakes:
https://www.youtube.com/watch?v=ev6XTdlKElw

Fun destroying brakes:
https://www.youtube.com/watch?v=KslGsXMgmqg The brake starting
at 4:45 sure looks like CF but I'm not sure.

Maybe twin disk brakes would be easier?
http://nuovafaor.it//public/prodotto/75/nccrop/DOPPIO_FRENO_CROSS_ENDURO.jpg


https://i.ytimg.com/vi/Pvwj-WWlKkg/maxresdefault.jpg
https://gzmyu4ma9b-flywheel.netdna-ssl.com/wp-content/uploads/2011/09/Gatorbrake-dual-hydraulic-front-disc-brakes-carbon-rotors01.jpg


https://lh4.googleusercontent.com/-cDfAFWrGR6Q/VHKPsm-f6YI/AAAAAAAAX10/2FCyj87xs0g/s640/14%2520-%25201.jpg
https://www.minibikecraze.co.uk/wp-content/uploads/bs0978.jpg
https://endless-sphere.com/forums/viewtopic.php?f=28&t=56268

Given the coefficient of friction between a 1.25" wide rubber tire
(32mm) and a wet road probably dragging the feet will work. :-)

Joerg's experience is with full suspension MTB's. These things are
incredibly heavy and long wheelbased. He has his judgement of disks
and it is no doubt quite accurate for his experience and riding..

I have disks on a much lighter and shorter wheelbased bike. I know
the failings up close and personal. I simply cannot imagine WHY a
person would want a more complicated system than that offered by the
Campy Skeleton brakes.


The reason can be summed up in one word: Rain :-)

But last Sunday I started out my "weekend" ride in the rain. It had
been raining nearly all night and the roads had a lot of water on them
- note we have been having floods here in Bangkok lately - but it
appeared that the rain was ending so off I went.

Unfortunately my weather forecasting facility wasn't working very well
and I rode 20 Km of a 30 Km ride in light rain and flooded roads in
many places. I was splashing through water in some places and cars
were splashing through (and splashing me) in others.

Of course, Sunday is much lighter traffic then on work days but still,
Bangkok is rated as one of the cities with the most chaotic traffic
in the world, and I did have to stop suddenly several time, on flooded
roads with wet wheels and brakes.

My brakes worked just as they do in the dry. Back brake stops me
somewhat slowly and front brake stops rather suddenly, both brakes
together provides best stopping. No long wait after grabbing a brake
lever although I did think of you with your stopping problems and I
have the feeling that the brake lever pressure might be a tiny bit
more to stop in the rain but if it was it was so little that it
couldn't be quantified.

But of course I am using quality brake pads. Why it costs me US$12.12
a wheel just for pads alone.... but they do last a year or more.


It seems Californian rain and Thai rain aren't the same. When it rains
heavily and I have to do a surprise emergency stop after not having used
the brakes for a while there is 1-2sec of nada, absolutely nothing.. It
makes no difference whatsoever whether I use $17 high-falutin Koolstop
rain-rated pads or $4 Clarks pads. The experience of other riders around
here and in this NG is similar.

Which, to be honest, I find a little mystifying as I've had pretty
constant success with conventional brakes.

Frankly, I can't believe this is solely because I'm somehow so
uniquely skilled or that y'all are all in the awkward squad

I do see a number of people here and many who are not here who seem to
have ridden for years using conventional brakes without complaint and
some of the blogs I read don't even talk about brakes. Dave Moulton,
for example. An old fellow, used to race bikes, came to the U.S. in
about 1979 and built frames commercially for years, now retired, has
one entry in his blog about brakes - "centering side pull brakes".

Another blog from the long distance side of the bicycleing world, The
Blayleys, who are into Audex's and who apparently each ride in the
neighborhood of 10,000 miles annually, mentions Vee brakes in
reference to a Tandem while a photo of them on a tandem on their web
page shows disc brakes. On the other hand, when she discusses a "good
brevet bike she simply says that the "brakes must clear the fenders
and probably long reach caliper brakes will suffice".

In short, it seems that brakes just don't seem to be a hot subject in
much of the cycling fraternity.


To a large part that is because most cyclist will not ride in driving
rain. Some do and those know exactly how that delay with rim brakes
feels. Occasionally it is called "free fall" because that's how it feels
like.

Well, the Blayleys state that the husband, John, has ridden 10 - 17
thousand miles a year for the past 25 years and the wife, Pamela, has
ridden from 10 - 14 thousand miles a year for the past 20 years, or
another way to put it might be that together they have ridden from 20
- 30 thousand miles a year for the past 20 years.

Somehow I suspect that they may have encountered rain in that period.


And grandpa has driven his cars without safety belts yet survived ...

For people who do not shy away from unpaved roads or use a lot of
singletrack and ride in the rain there is a much more extreme issue: Wet
mud. You may have never encountered it but I have many times. You reach
in and, after a second or two of nothing, the rim brakes come on but let
off an awful grinding noise. You can literally hear the rim being
tortured but because of a rapidly approaching curve you can't let go. As
I have mentioned before the rims on my old MTB are only 1000mi old but
the front rim is almost shot from all that. Deep grooves.

I stand by my opinion that rim brakes are fair weather brakes. Then they
are fine but not when the going gets tough. Like this kind of weather:

https://www.youtube.com/watch?v=mX_EKybzK4Y


I might comment that I've ridden coaster brakes, drum brakes, rod pull
brakes, cantilever brakes, side pull single pivot caliper brakes,
double pivot caliper, Vee brakes and for one short ride a cable disc
brake. and at the time I rode them I found all the brakes to give
acceptable service. Well with one exception, rim brakes and chrome
plated steel rims were sometimes a bit iffy :-)


Yes, those were the worst. It got a little better with aluminum rims but
not a lot. In the world of automotive such a brake "system" would not
stand the slightest change of being legal.

Finally after many decades the bicycle industry woke up and adopted what
the automotive guys had all along, disc brakes. Why should I accept an
inferior brake system on a new bike when there is a much better one?

Well, when I worked on airplanes I remember that the F-4 had multi
plate disc brakes which provided a tremendous amount of stopping power
in a very small package.


Some tandems have that as well, and of course motorcycles: Two discs up
front. But not stacks of discs.


One supposes that will be next big improvement in bicycle brakes. Or
perhaps a drag chute for those long downhill's to keep the rims from
melting?


I've thought about it :-)

--
Regards, Joerg

http://www.analogconsultants.com/

Oh ****! I've ridden many hundreds of miles off road in dry and wet sand, mud, heavy rain, rutted roads/trails and did so on an MTB with cantilever brakes and NEVER had trouble stopping either when I needed to or when I wanted too. I've ridden on ice and in 4 inches+ deep snowand also never had trouble stopping.

Perhaps you ride too fast for the conditions/sight lines or you don't keep your brakes adjusted properly.

Now that reads far more reasonably. I can't remember riding in snow and probably haven't but I have ridden in hail that quickly covered the entire road on a steep downhill. Pretty scary but from tire traction and not braking system requirements.

On 2017-10-29 08:22, wrote:
On Friday, October 27, 2017 at 5:11:29 PM UTC-7, John B. wrote:

Well, the Blayleys state that the husband, John, has ridden 10 -
17 thousand miles a year for the past 25 years and the wife,
Pamela, has ridden from 10 - 14 thousand miles a year for the past
20 years, or another way to put it might be that together they have
ridden from 20 - 30 thousand miles a year for the past 20 years.

Somehow I suspect that they may have encountered rain in that
period.

For three years while between jobs I road almost continuously
including several long distance tours each year. I barely made 10,000
miles per year and usually only cleared that hurdle with a last
minute sprint. So unless the Blayley's are on a continuous tour I
would question those miles.


I don't know who the Blayleys are but I am only riding 2-3 times a week
and between the MTB and the road bike the odometers clock a total of
about 4000mi/year. When I fully retire I can hopefully add in another
ride or two and beef one ride up to all-day. That can easily put people
to 10000mi. During my university days I was around 6000mi/year and still
had a 19h/week job plus had to study for my degree. However, like today
I used a bike for every errand or journey if at all possible.

Last year my car rolled all of 757mi. Got to start thinking about a
battery tender.

--
Regards, Joerg

http://www.analogconsultants.com/

On Saturday, October 28, 2017 at 4:59:49 PM UTC-7, jbeattie wrote:
On Saturday, October 28, 2017 at 3:40:36 PM UTC-7, AMuzi wrote:
On 10/28/2017 4:27 PM, jbeattie wrote:
On Saturday, October 28, 2017 at 12:08:44 PM UTC-7, Sir Ridesalot wrote:
On Saturday, October 28, 2017 at 11:09:18 AM UTC-4, Joerg wrote:
On 2017-10-27 17:11, John B. wrote:
On Fri, 27 Oct 2017 06:58:27 -0700, Joerg
wrote:

On 2017-10-27 01:11, John B. wrote:
On Wed, 25 Oct 2017 07:53:11 -0700, Joerg
wrote:

On 2017-10-24 17:21, John B. wrote:
On Tue, 24 Oct 2017 11:47:12 -0700, Joerg
wrote:

On 2017-10-24 07:27, wrote:
On Tuesday, October 24, 2017 at 2:19:48 AM UTC-7, John B. wrote:
On Mon, 23 Oct 2017 10:09:20 -0700, Jeff Liebermann
wrote:

On Mon, 23 Oct 2017 12:48:29 +0700, John B.
wrote:

On Sun, 22 Oct 2017 20:51:15 -0700, Jeff Liebermann
wrote:

On Mon, 23 Oct 2017 07:02:08 +0700, John B.
wrote:

But re disc brake cooling F1 car brakes appear to work with
the discs red hot. In the 1,000 degree (F) range. And they
use Carbon Fiber discs too :-) And everyone knows that CF
is better.

"Thermal Conductivity of Carbon Fiber, and other Carbon
Based Materials"
http://www.christinedemerchant.com/carbon_characteristics_heat_conductivity.html


"So...Is Carbon Fiber a good heat conductor?
As usual the answer is "it depends." The short answer is NO
not when regular carbon fiber is made up in regular epoxy and
expected to conduct heat across the thickness. IF a highly
carbonized pan fiber with graphite or diamond added, is
measured for heat transmission in the length of the fiber it
is very good and can rival and exceed copper."

On the other hand, they seem to work pretty well :-) See
https://www.youtube.com/watch?v=h5JcHAEmIYM for a visual
indication of heat dissipation. :-)

Impressive. I'll assume it's a carbon-carbon rotor, since all F1
cars seem to using them.

Undoubtedly so. But if the advantage of "carbon" bikes can be
extolled that a carbon-carbon frame must have twice the bragging
rights :-)


http://www.racecar-engineering.com/technology-explained/f1-2014-explained-brake-systems/


(4 pages)
"A typical road car uses a cast iron brake disc with an organic
brake pad. In an F1 car, though, the same material is used for
both disc and pad, and this material is known as carbon-carbon -
a significantly different material to the carbon-fibre
composites used in the rest of the car" In other words, the F1
brakes are NOT made from CF.

Some detail on Formula 1 brakes:
https://www.youtube.com/watch?v=ev6XTdlKElw

Fun destroying brakes:
https://www.youtube.com/watch?v=KslGsXMgmqg The brake starting
at 4:45 sure looks like CF but I'm not sure.

Maybe twin disk brakes would be easier?
http://nuovafaor.it//public/prodotto/75/nccrop/DOPPIO_FRENO_CROSS_ENDURO.jpg


https://i.ytimg.com/vi/Pvwj-WWlKkg/maxresdefault.jpg
https://gzmyu4ma9b-flywheel.netdna-ssl.com/wp-content/uploads/2011/09/Gatorbrake-dual-hydraulic-front-disc-brakes-carbon-rotors01.jpg


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https://www.minibikecraze.co.uk/wp-content/uploads/bs0978..jpg
https://endless-sphere.com/forums/viewtopic.php?f=28&t=56268

Given the coefficient of friction between a 1.25" wide rubber tire
(32mm) and a wet road probably dragging the feet will work. :-)

Joerg's experience is with full suspension MTB's. These things are
incredibly heavy and long wheelbased. He has his judgement of disks
and it is no doubt quite accurate for his experience and riding.

I have disks on a much lighter and shorter wheelbased bike. I know
the failings up close and personal. I simply cannot imagine WHY a
person would want a more complicated system than that offered by the
Campy Skeleton brakes.


The reason can be summed up in one word: Rain :-)

But last Sunday I started out my "weekend" ride in the rain. It had
been raining nearly all night and the roads had a lot of water on them
- note we have been having floods here in Bangkok lately - but it
appeared that the rain was ending so off I went.

Unfortunately my weather forecasting facility wasn't working very well
and I rode 20 Km of a 30 Km ride in light rain and flooded roads in
many places. I was splashing through water in some places and cars
were splashing through (and splashing me) in others.

Of course, Sunday is much lighter traffic then on work days but still,
Bangkok is rated as one of the cities with the most chaotic traffic
in the world, and I did have to stop suddenly several time, on flooded
roads with wet wheels and brakes.

My brakes worked just as they do in the dry. Back brake stops me
somewhat slowly and front brake stops rather suddenly, both brakes
together provides best stopping. No long wait after grabbing a brake
lever although I did think of you with your stopping problems and I
have the feeling that the brake lever pressure might be a tiny bit
more to stop in the rain but if it was it was so little that it
couldn't be quantified.

But of course I am using quality brake pads. Why it costs me US$12.12
a wheel just for pads alone.... but they do last a year or more.


It seems Californian rain and Thai rain aren't the same. When it rains
heavily and I have to do a surprise emergency stop after not having used
the brakes for a while there is 1-2sec of nada, absolutely nothing. It
makes no difference whatsoever whether I use $17 high-falutin Koolstop
rain-rated pads or $4 Clarks pads. The experience of other riders around
here and in this NG is similar.

Which, to be honest, I find a little mystifying as I've had pretty
constant success with conventional brakes.

Frankly, I can't believe this is solely because I'm somehow so
uniquely skilled or that y'all are all in the awkward squad

I do see a number of people here and many who are not here who seem to
have ridden for years using conventional brakes without complaint and
some of the blogs I read don't even talk about brakes. Dave Moulton,
for example. An old fellow, used to race bikes, came to the U.S. in
about 1979 and built frames commercially for years, now retired, has
one entry in his blog about brakes - "centering side pull brakes".

Another blog from the long distance side of the bicycleing world, The
Blayleys, who are into Audex's and who apparently each ride in the
neighborhood of 10,000 miles annually, mentions Vee brakes in
reference to a Tandem while a photo of them on a tandem on their web
page shows disc brakes. On the other hand, when she discusses a "good
brevet bike she simply says that the "brakes must clear the fenders
and probably long reach caliper brakes will suffice".

In short, it seems that brakes just don't seem to be a hot subject in
much of the cycling fraternity.


To a large part that is because most cyclist will not ride in driving
rain. Some do and those know exactly how that delay with rim brakes
feels. Occasionally it is called "free fall" because that's how it feels
like.

Well, the Blayleys state that the husband, John, has ridden 10 - 17
thousand miles a year for the past 25 years and the wife, Pamela, has
ridden from 10 - 14 thousand miles a year for the past 20 years, or
another way to put it might be that together they have ridden from 20
- 30 thousand miles a year for the past 20 years.

Somehow I suspect that they may have encountered rain in that period.


And grandpa has driven his cars without safety belts yet survived ....

For people who do not shy away from unpaved roads or use a lot of
singletrack and ride in the rain there is a much more extreme issue: Wet
mud. You may have never encountered it but I have many times. You reach
in and, after a second or two of nothing, the rim brakes come on but let
off an awful grinding noise. You can literally hear the rim being
tortured but because of a rapidly approaching curve you can't let go. As
I have mentioned before the rims on my old MTB are only 1000mi old but
the front rim is almost shot from all that. Deep grooves.

I stand by my opinion that rim brakes are fair weather brakes. Then they
are fine but not when the going gets tough. Like this kind of weather:

https://www.youtube.com/watch?v=mX_EKybzK4Y


I might comment that I've ridden coaster brakes, drum brakes, rod pull
brakes, cantilever brakes, side pull single pivot caliper brakes,
double pivot caliper, Vee brakes and for one short ride a cable disc
brake. and at the time I rode them I found all the brakes to give
acceptable service. Well with one exception, rim brakes and chrome
plated steel rims were sometimes a bit iffy :-)


Yes, those were the worst. It got a little better with aluminum rims but
not a lot. In the world of automotive such a brake "system" would not
stand the slightest change of being legal.

Finally after many decades the bicycle industry woke up and adopted what
the automotive guys had all along, disc brakes. Why should I accept an
inferior brake system on a new bike when there is a much better one?

Well, when I worked on airplanes I remember that the F-4 had multi
plate disc brakes which provided a tremendous amount of stopping power
in a very small package.


Some tandems have that as well, and of course motorcycles: Two discs up
front. But not stacks of discs.


One supposes that will be next big improvement in bicycle brakes. Or
perhaps a drag chute for those long downhill's to keep the rims from
melting?


I've thought about it :-)

--
Regards, Joerg

http://www.analogconsultants.com/

Oh ****! I've ridden many hundreds of miles off road in dry and wet sand, mud, heavy rain, rutted roads/trails and did so on an MTB with cantilever brakes and NEVER had trouble stopping either when I needed to or when I wanted too. I've ridden on ice and in 4 inches+ deep snowand also never had trouble stopping.

Perhaps you ride too fast for the conditions/sight lines or you don't keep your brakes adjusted properly.

Really? I have trouble standing up on ice. There is a point at which you don't want super-strong brakes.

-- Jay Beattie.


Yeah me too.
Snow is one thing - I'm used to that- but ice is quite
another. Depending on the recent weather, a frozen slick
patch of ice under snow will dump me right on my ass. We
mere humans would have some trouble with Jobst's famous tour
down a frozen Swiss river.

I live at a whopping 400 feet (about) elevation. The garage in my building is probably 0 feet. That minor elevation change sometimes means the difference between ice and no ice -- so I walk outside in the morning and say f*** this! And then I jump in the car and half-way to work, creeping along in traffic, there is no ice -- and then I regret not riding. So, in order to avoid that regret, I have done some pretty stupid sh** spinning around on ice or hoofing it in my SPDs to get out of my neighborhood and then being freaked out riding over the slick bridges and viaducts into town. I met up with another guy on a bike who was fish-tailing down the road on one of those mornings, and we looked at each other and shook our heads -- "we're a couple of idiots." So, now I'm working on not feeling regret or guilt if I drive. And don't get me going about the dopes who jump into their Malibus with no-season/no-tread tires and crash on the ice and/or snow. I'll slap on the snow tires in November. I really miss studs, but I'm doing penance with studless.

What sort of clothes do you wear to ride to work? And do you change at work or what?

A local job in a very convenient location is probably within riding distance but the position (at HALF of what it should be paying) will probably need neat attire.

On 10/29/2017 12:41 PM, wrote:
On Friday, October 27, 2017 at 11:24:01 PM UTC-7, Ralph Barone wrote:

Sure. But the distance you can move your brake lever is limited by the
length of your fingers, and so the distance you can move at the lever end
is essentially fixed. To increase the mechanical advantage in THAT system,
you have to reduce the distance the brake pads move. No ifs, ands, buts or
maybes.

This is only in linear systems. The new Skeleton Campy brakes open further and the brakes close to perhaps 3/32nds from the rim. This gives you immense leverage. They really are quite amazing.

OK, I'm curious about that brake mechanism. I didn't realize they did
anything unusual. How do they work?


--
- Frank Krygowski

On 2017-10-29 09:45, wrote:
On Saturday, October 28, 2017 at 8:09:18 AM UTC-7, Joerg wrote:

And grandpa has driven his cars without safety belts yet survived
...

For people who do not shy away from unpaved roads or use a lot of
singletrack and ride in the rain there is a much more extreme
issue: Wet mud.

There is NO brake the is proof against wet mud. In fact it is perhaps
worse on a disk since the additional pressure of the pads can turn
the silicon present in most muds into cutting instruments that on rim
brakes cuts into the rubber show rather than the hard and thin disk
pad.


Actually, no. I've had mud literally dripping from the calipers which
had become barely recognizable brownish blobs. The only thing that
happens is that they make an awful grinding noise just like muddy rim
brakes do. With the two major differences that they still come on full
force immediately and that this grinding does not eat up aluminum.
Aluminum as one of the braking surfaces plain does not make any sense,
certainly not in a muddy environment.

A downside of bicycle disc brakes is that in contrast to most motor
vehicles the rotors have "vent holes" and weight weenie spiders. This
results in rather fast heat-up and in "brake mousse" when you plow
through thick vegetation on an overgrown trail. Mashed star-thistle and
other weeds get shredded and a sort of pulp develops which cakes up in
the holes of the rotor. It doesn't diminish the brake force but lets of
a bad stench. One of the reasons why I carry a Swiss Army knife in a
pocket. Not in a pannier, so I can whip it out in seconds. This also
helps in poking out the giant mud clump that forms behind the BB and can
prevent the rear wheel from turning.

--
Regards, Joerg

http://www.analogconsultants.com/