Another argument for disk brakes?

Sorry I didn't attach this to the "Disk vs. V-brake" thread; I don't
have access to the thread's ancestors...

I ride a 26-20 lowracer
(http://hebb.mit.edu/~ben/bike/side_naked_unoccupied.png). I live in
Boulder, CO, USA, which presents numerous opportunities for rides with
enormous altitude gain--at least to those stronger than I. The
problem with altitude gain is the altitude loss. I've heard a rumour
that rim brakes on a 20" rim over long descents can dump enough heat
into the wheel that it actually melts the tube.

Anyone else heard of this? Does it sound plausible?

And while we're on the topic, what's the current story with this?:
http://www.ne.jp/asahi/julesandjames...ase/index.html
(ie. disk brakes put vastly more force on your front dropout quick
release than it was designed for)

Cheers!
-Ben

Please excuse the email address mangling...

--
Ben Pearre http://hebb.mit.edu/~ben PGP: CFDA6CDA
Free music at http://hebb.mit.edu/FreeMusic
Don't let Bush read your email! http://www.gnupg.org

Ben Pearre wrote:
Sorry I didn't attach this to the "Disk vs. V-brake" thread; I don't
have access to the thread's ancestors...

I ride a 26-20 lowracer
(http://hebb.mit.edu/~ben/bike/side_naked_unoccupied.png). I live in
Boulder, CO, USA, which presents numerous opportunities for rides with
enormous altitude gain--at least to those stronger than I. The
problem with altitude gain is the altitude loss. I've heard a rumour
that rim brakes on a 20" rim over long descents can dump enough heat
into the wheel that it actually melts the tube.

Anyone else heard of this? Does it sound plausible?

i've seen a failure that looked remarkably like this.


And while we're on the topic, what's the current story with this?:
http://www.ne.jp/asahi/julesandjames...ase/index.html
(ie. disk brakes put vastly more force on your front dropout quick
release than it was designed for)

/that/ is a thoroughly discreditable "chicken little" story.

1. for a correctly mounted wheel*, pullout force exceeds ejection force
many times. annan "neglected" the fact that serrated axle faces bite
into fork ends to make the pullout process require shear though a
substantial amount of material.

2. the presence of "lawyer lips" is completely disregarded.

in the face of both these serious omissions, together with the fact that
no one here [with the exception of annan himself of course] has
experienced such an ejection, we can pretty much discount this "alarm".
you can /rely/ on this group for the delight in corroboration of a
horror story if it were possible.

google this group for the archive on this debate.


* the only possible way for the front axle to come loose is if it's not
mounted correctly or the axle assembly fails. the first is operator
error - just like not fastening a brake cable clamp or even mounting
brake pads the wrong way around. the second is a disaster anyway and is
nothing to to with the brake. see sheldon's excellent article on quick
skewers for clarification.

http://sheldonbrown.com/skewers.html


Cheers!
-Ben

Please excuse the email address mangling...

--
Ben Pearre http://hebb.mit.edu/~ben PGP: CFDA6CDA
Free music at http://hebb.mit.edu/FreeMusic
Don't let Bush read your email! http://www.gnupg.org

Ben Pearre wrote:
Sorry I didn't attach this to the "Disk vs. V-brake" thread; I don't
have access to the thread's ancestors...

I ride a 26-20 lowracer
(http://hebb.mit.edu/~ben/bike/side_naked_unoccupied.png). I live in
Boulder, CO, USA, which presents numerous opportunities for rides with
enormous altitude gain--at least to those stronger than I. The
problem with altitude gain is the altitude loss. I've heard a rumour
that rim brakes on a 20" rim over long descents can dump enough heat
into the wheel that it actually melts the tube.

Anyone else heard of this? Does it sound plausible?


rim heating from braking is well known to cause failure in tandems or
other bikes carrying heavy loads on 700c wheels. Seems plausible that a
20 inch wheel would heat up faster than a 700c, so it may be a worry on
'bents. It's never been clear to me that the tube actually melts, I've
always thought it was the rim/tire interface getting "slippery" and then
the tire shifts, causing the valve to sheer off. I've also heard the
higher pressure in the tire caused by heat blamed, but since the
pressure rise is proportional to the rise in absolute temperature, I've
never really believed this would cause failure unless the tire was way
overinflated or already suspect in some way.

Whatever the reason for failure, it does happen, and disk brakes do help
in this regard. They will fail from heat, but at least you don't lose
the tire when it happens.

Baird

jim beam wrote:
Ben Pearre wrote:

And while we're on the topic, what's the current story with this?:
http://www.ne.jp/asahi/julesandjames...ase/index.html
(ie. disk brakes put vastly more force on your front dropout quick
release than it was designed for)

/that/ is a thoroughly discreditable "chicken little" story.

Some very knowledgeable people disagree. And not all of them are
people Jim Beam is pursuing with a vendetta. See
http://www.ne.jp/asahi/julesandjames...e/experts.html



1. for a correctly mounted wheel*, pullout force exceeds ejection force
many times. annan "neglected" the fact that serrated axle faces bite
into fork ends to make the pullout process require shear though a
substantial amount of material.

Who was that prominent British mountain biker who was paralyzed in an
accident when his disk brake ejecting his front wheel? Apparently, his
bike "neglected" the same thing.

- Frank Krygowski

wrote:
jim beam wrote:

Ben Pearre wrote:


And while we're on the topic, what's the current story with this?:
http://www.ne.jp/asahi/julesandjames...ase/index.html
(ie. disk brakes put vastly more force on your front dropout quick
release than it was designed for)

/that/ is a thoroughly discreditable "chicken little" story.


Some very knowledgeable people disagree. And not all of them are
people Jim Beam is pursuing with a vendetta. See
http://www.ne.jp/asahi/julesandjames...e/experts.html

4 people out of how many? 4 people & only 1 is an engineer? and that
engineer is jobst brandt??? and jobst's credentials include such
masterpieces as the non-brinelling headset bearing, the stainless steel
spoke with an endurance limit, the wheel whose strength increases as
spoke tension increases, etc. sure, that's a mighty mighty weight of
support.




1. for a correctly mounted wheel*, pullout force exceeds ejection force
many times. annan "neglected" the fact that serrated axle faces bite
into fork ends to make the pullout process require shear though a
substantial amount of material.


Who was that prominent British mountain biker who was paralyzed in an
accident when his disk brake ejecting his front wheel? Apparently, his
bike "neglected" the same thing.

- Frank Krygowski

with respect frank, and with no disrespect to the injured, where's the
proof this alledged ejection, that managed to overcome a properly fitted
skewer /and/ lawyer lips, wasn't due to incompetency? "er, yeah, i
checked that skewer". just like the tire shop that "checks" lug nuts on
the car whose wheel falls off 50 miles down the road.

On 2005-09-13, jim beam wrote:
/that/ is a thoroughly discreditable "chicken little" story.

I'm so sorry, but I have not seen it creditably discredited yet. I
was hoping someone here would do me that favour.

If your arguments included a verifiably better explanation of the
geometry, forces that will be on the parts, updated specs showing
large safety margins, etc, I would be more comforted. Or even if you
gave me numbers to show that the serrations, lawyer lips, etc, are now
being designed to competently handle the new forces...? AFAIK they're
still designed as a last line of defense against a fairly gentle
operator error.

1. for a correctly mounted wheel*, pullout force exceeds ejection force
many times. annan "neglected" the fact that serrated axle faces bite
into fork ends to make the pullout process require shear though a
substantial amount of material.

The serrations on the axle are designed for forces that didn't include
disk brake ejection. It seems stupid to rely on these--and lawyer
lips!!--when having the axle actually bear against a solid piece of
enclosure is the correct solution.

For example, would you be comfortable riding an unsuspended bike with
the dropouts mounted upside-down? You're welcome to your lawyer lips
and serrations, mind, but every time you hit a bump or even got on the
bike I hope you'd be wondering how reliable that was. Otherwise you
have more faith in bicycle engineers than I do!

The article describing the problem got the geometry right and got the
math very plausible, and for my bike the effect would be even greater
since I can put more ejection force on my front wheel than most of you
guys can

2. the presence of "lawyer lips" is completely disregarded.

No, it's just _mostly_ disregarded (search the article). Besides, as
the lips' name should suggest, they are not designed as structural
elements in the wheel system, merely as a last line of defense against
operator error. Why orient the brakes to rely on them when you could
easily fix the geometry? Of course, no fix to the geometry (besides
larger disks) will do anything for the risk of the skewers shearing
off Any reports of skewer breakage? My own numbers indicate that
this should be nigh-impossible, but I've made some questionable
assumptions...

in the face of both these serious omissions, together with the fact that
no one here [with the exception of annan himself of course] has
experienced such an ejection, we can pretty much discount this "alarm".

A low failure rate is most comforting. After all, we all take risks
all the time, and we need to balance them against the benefits. So:
what benefit do I get in exchange for this particular risk?

you can /rely/ on this group for the delight in corroboration of a
horror story if it were possible.

I think I am coming to agree with this very quickly Sorry if
contributing it is bad form...

google this group for the archive on this debate.

Thanks for that Good point!

Regarding "operator error"--of course there are some things for which
the designer must trust the user. Not much the engineer can do about
the operator choosing to steer the bike into a tree. But here the
situation is different: there _are_ parts that _can_ be highly loaded
in a direction that was never designed to see high load. Operator
error will compound the problem, but requiring the operator to be
fully conscious of the new requirements of the system, the risks, and
the FACT THAT THE SYSTEM HAS NO SAFETY MARGIN is inexcusable, even if
the problem is clearly and conspicuously documented in the user manual
AND there's an admonition never ever, on pain of death (this should be
stronger than "void your warranty"), to use aftermarket skewers!
Anyone see either of these? (besides, as a software developer, I know
firsthand how many people read the product manuals...)

If there is a good argument for the possibility of a problem, then
it's stupid to wait for "more proof" if "more proof" will involve bad
things like death. If I'm on my bike and there's a driver weaving
back and forth all over the road, I could say "he's drunk" and get off
the road, or I could say "there's no documented proof that he's drunk;
I don't need to do anything yet." Come ON! Next you'll tell me that
there's no concrete proof for global warming so we may as well not do
anything to save ourselves against a threat that's merely plausible.

Oh, and attacking someone's past work does nothing whatsoever to
weaken his current well-documented argument. Rather the reverse.

Cheers
-Ben

--
Ben Pearre http://hebb.mit.edu/~ben PGP: CFDA6CDA
Free music at http://hebb.mit.edu/FreeMusic
Don't let Bush read your email! http://www.gnupg.org

Ben Pearre wrote:
Sorry I didn't attach this to the "Disk vs. V-brake" thread; I don't
have access to the thread's ancestors...

I ride a 26-20 lowracer
(http://hebb.mit.edu/~ben/bike/side_naked_unoccupied.png). I live in
Boulder, CO, USA, which presents numerous opportunities for rides with
enormous altitude gain--at least to those stronger than I. The
problem with altitude gain is the altitude loss.

There is a fix for this; don't brake ;-)

I've heard a rumour
that rim brakes on a 20" rim over long descents can dump enough heat
into the wheel that it actually melts the tube.

I've seen few roads in the US where the runs are long enough and steep
enough for one to need to brake excessively and overheat the rims with
rim braking. So the question is really, can it happen, under what
conditions can it happen, and do those conditions exist in the areas
you ride. I grew up in the Rockies, have ridden all around in them,
and cannot think of anyplace in particular with enough of a run at a
steep enough grade to be much of an issue. Now if we were talking the
Alps, then .....


- rick

On 13 Sep 2005 19:31:05 GMT, Ben Pearre
wrote:

On 2005-09-13, jim beam wrote:
/that/ is a thoroughly discreditable "chicken little" story.

If there is a good argument for the possibility of a problem, then
it's stupid to wait for "more proof" if "more proof" will involve bad
things like death..... Next you'll tell me that
there's no concrete proof for global warming so we may as well not do
anything to save ourselves against a threat that's merely plausible.
Cheers
-Ben

I was with you all the way to the bit about global warming - the
evidence for conventional front dropouts being bad news with disc
brakes is much stronger than that for global warming being either a:
anthropogenic b: a bad thing or c: reversible by policy change, all
of which are highly speculative and susceptible to differences not
only of data interpretation but of opinion. I'm not trying to
initiate an argument about any of these "global warming" issues, just
pointing out that it's a weak analogy if you're trying to persuade
somebody about the authentic, verifiable and mathematically simple
problem of wheel ejection.

The planet can go to hell (or not), but I'm saving myself by switching
to 20mm through axle forks :-)

Kinky Cowboy*

*Batteries not included
May contain traces of nuts
Your milage may vary

Per Ben Pear
/that/ is a thoroughly discreditable "chicken little" story.

I'm so sorry, but I have not seen it creditably discredited yet. I
was hoping someone here would do me that favour.

The one thing that I can see doing somebody in is total skewer failure. Dunno
how that happens - or if it happens.... but that would definitely do the trick.


As long as the skewer is intact, the lawyer lips seem to do their job pretty
well. One day the bike felt funny. I checked the front wheel and the skewer
had come loose - quite loose. How? RCI? Vibration from a long road trip?
Dunno... but that sucker was *loose*. Now I try to check it every time before
riding. Haven't got myself fully trained yet - but I'm working on it.

--
PeteCresswell

Ben Pearre wrote:
On 2005-09-13, jim beam wrote:

/that/ is a thoroughly discreditable "chicken little" story.


I'm so sorry, but I have not seen it creditably discredited yet. I
was hoping someone here would do me that favour.

If your arguments included a verifiably better explanation of the
geometry, forces that will be on the parts, updated specs showing
large safety margins, etc, I would be more comforted.

that's been done. google is your friend.

Or even if you
gave me numbers to show that the serrations, lawyer lips, etc, are now
being designed to competently handle the new forces...? AFAIK they're
still designed as a last line of defense against a fairly gentle
operator error.


1. for a correctly mounted wheel*, pullout force exceeds ejection force
many times. annan "neglected" the fact that serrated axle faces bite
into fork ends to make the pullout process require shear though a
substantial amount of material.


The serrations on the axle are designed for forces that didn't include
disk brake ejection.

that's what annan would have you believe, and you bought it.

It seems stupid to rely on these--and lawyer
lips!!--when having the axle actually bear against a solid piece of
enclosure is the correct solution.

but it's not so good for quick roadside puncture repair.

bottom line, if a skewer can clamp & achieve a pullout force of 5000N
and experiences a max of 1800N in service, it there a problem or not?
bear in mind that your answer also needs to accord with the reality of
what is seen in countless thousands of disk braked mtb's all over the globe.


For example, would you be comfortable riding an unsuspended bike with
the dropouts mounted upside-down?

hmm, you need to read this article:
http://sheldonbrown.com/hercules.html
scroll down or search for "Bianchi Osprey".

You're welcome to your lawyer lips
and serrations, mind, but every time you hit a bump or even got on the
bike I hope you'd be wondering how reliable that was. Otherwise you
have more faith in bicycle engineers than I do!

ones that know their business, yes!


The article describing the problem got the geometry right and got the
math very plausible, and for my bike the effect would be even greater
since I can put more ejection force on my front wheel than most of you
guys can


2. the presence of "lawyer lips" is completely disregarded.


No, it's just _mostly_ disregarded (search the article).

now that's /really/ straw clutching.

Besides, as
the lips' name should suggest, they are not designed as structural
elements in the wheel system, merely as a last line of defense against
operator error. Why orient the brakes to rely on them when you could
easily fix the geometry? Of course, no fix to the geometry (besides
larger disks) will do anything for the risk of the skewers shearing
off Any reports of skewer breakage? My own numbers indicate that
this should be nigh-impossible, but I've made some questionable
assumptions...

so, just clarify your position for me: is a failed skewer somehow worse
than a failed fork crown? how about brake line? handlebar? how about
a flat that bunches the tire up in the fork & locks the wheel? [i've
got the scars on that one.] reality is, every single component on the
bike can fail in some way. the question is, what is the /probability/
of failure.



in the face of both these serious omissions, together with the fact that
no one here [with the exception of annan himself of course] has
experienced such an ejection, we can pretty much discount this "alarm".


A low failure rate is most comforting. After all, we all take risks
all the time, and we need to balance them against the benefits. So:
what benefit do I get in exchange for this particular risk?

well, you /do/ have, a low failure rate. seriously, has anyone other
than annan experienced ejection here? i fully sympathize with, and am
fully aware of pete cresswell's scenario, and i did in fact experience
that myself once on a road bike, but on examination, i'd not seated the
cup washer under the open cam skewer mechanism properly. i may not
enjoy admitting it, but that was operator error, no excuse.



you can /rely/ on this group for the delight in corroboration of a
horror story if it were possible.


I think I am coming to agree with this very quickly Sorry if
contributing it is bad form...

recognition of reality is better form.



google this group for the archive on this debate.


Thanks for that Good point!

Regarding "operator error"--of course there are some things for which
the designer must trust the user. Not much the engineer can do about
the operator choosing to steer the bike into a tree. But here the
situation is different: there _are_ parts that _can_ be highly loaded
in a direction that was never designed to see high load. Operator
error will compound the problem, but requiring the operator to be
fully conscious of the new requirements of the system, the risks, and
the FACT THAT THE SYSTEM HAS NO SAFETY MARGIN

no safety margin? 5000N vs 1800N??? are you serious? and the fact
that you have lawyer lips on top of that is of no consequence? how much
more "SAFETY MARGIN" do you need? some minor fudges aside, annan's math
is fine, right up until the point where he fails to bother analyzing the
pullout force side of the equation. that's the beauty of a scary story
- is that frayed old piece of rope /really/ the big scary monster's tail
where he's hiding behind the rock? or is it just a piece of old rope?

is inexcusable, even if
the problem is clearly and conspicuously documented in the user manual
AND there's an admonition never ever, on pain of death (this should be
stronger than "void your warranty"), to use aftermarket skewers!
Anyone see either of these? (besides, as a software developer, I know
firsthand how many people read the product manuals...)

now you're playing the sensation game.


If there is a good argument for the possibility of a problem, then
it's stupid to wait for "more proof" if "more proof" will involve bad
things like death. If I'm on my bike and there's a driver weaving
back and forth all over the road, I could say "he's drunk" and get off
the road, or I could say "there's no documented proof that he's drunk;
I don't need to do anything yet." Come ON! Next you'll tell me that
there's no concrete proof for global warming so we may as well not do
anything to save ourselves against a threat that's merely plausible.

well, leaving the looney global warming rant aside, you're getting all
frothy about the possibility of failure. if that's such a concern for
you, you'd better not ever fly in a plane. i mean, 3 major airliners in
august alone if i'm not mistaken. how about tower cranes? they fall
over all the time. elevators? cars? you could even be struck by
meteorite sitting alone in your hardened anti-technology bunker.

reality is, any human endeavor carries risk. the smart ones assess the
/probability/ of failure. for wheel ejection, the probability is such
that you can happily ride a disk braked bike for many thousands of miles
over several years and never see the slightest evidence of ejection.
ever. google is your friend.

Oh, and attacking someone's past work does nothing whatsoever to
weaken his current well-documented argument. Rather the reverse.

er, annan has had ample time to revise his work, collect corroborative
evidence and receive endorsement of credible engineers... instead, we
have highly selective sensationalistic drum beating - and increasing
adoption of disk brakes across a very highly populated sample group
whose use failure stats are in direct contradiction of annan's predictions.


Cheers
-Ben

--
Ben Pearre http://hebb.mit.edu/~ben PGP: CFDA6CDA
Free music at http://hebb.mit.edu/FreeMusic
Don't let Bush read your email! http://www.gnupg.org