Another argument for disk brakes?

Ben Pearre said:

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 said:

Ben Pearre said:

And while we're on the topic, what's the current story with this?:
http://www.ne.jp/asahi/julesandjames/home/disk_and_quick_release/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/home/disk_and_quick_release/experts.html

Quoted message said:

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

Quoted message said:

jim beam said:

Ben Pearre said:

And while we're on the topic, what's the current story with this?:
http://www.ne.jp/asahi/julesandjames/home/disk_and_quick_release/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/home/disk_and_quick_release/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.

Quoted message said:

Quoted message said:

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.

jim beam said:

/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.

Quoted message said:

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 🙂

Quoted message said:

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...

Quoted message said:

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?

Quoted message said:

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...

Quoted message said:

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 said:

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 ;-)

Quoted message said:

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

In article <[email hidden]>,

Ben Pearre said:

jim beam said:

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

Quoted message said:

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.

The lawyer lips on a suspension fork are a rather substantial counter
bore. I've had an mtb with disc brakes for almost a year, and I have
noticed no loosening of the skewer. In practice, I have not observed a
problem.

--
Mike DeMicco <[email hidden]>

Per Ben Pearre:

Quoted message said:

Quoted message said:

/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

Quoted message said:

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.

Don't the brake blocks melt first?

Quoting Rick <[email hidden]>:

Quoted message said:

Ben Pearre said:

I ride a 26-20 lowracer
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.

Well, the trouble is, he has a smaller rim and much lower air resistance;
just as tandems have this problem with twice the weight behind normal air
resistance.

The OP might want to read Santana's disc testing experiences before
assuming they are the answer; I don't suppose it's feasble to fit a drum
brake...
--
David Damerell <[email hidden]> flcl?
Today is Teleute, September.

Ben Pearre said:

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?

ISTR that even on larger rims, heat buildup on long, steep descents is
known to be able to induce blowouts, though I don't recall what the
exact mechanism of failure was determined to be. I believe that Jobst
Brandt had some testing planned to try to gather hard data.

My opinion is that while disk brakes would eliminate the rim heating
cited, their suitability for use in such applications needs to be
evaluated in terms of the capabilities of the specific disk setup in
question, and the stresses that will be applied. All disk brakes are
not created equal, and some may have fade, warpage, and/or durability
issues in high-load and high-heat applications.

Quoted message said:

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

The current story is that while there are cases of disk ejection,
there are far more cases of disk brake setups staying together just
fine. Thus far, the USCPSC has nof found sufficient evidence to merit
any action on the subject beyond just looking at it to see if there's
a serious problem.
--
Typoes are a feature, not a bug.
Some gardening required to reply via email.
Words processed in a facility that contains nuts.

David Damerell said:

Quoting Rick <[email hidden]>:

Quoted message said:

Ben Pearre said:

I ride a 26-20 lowracer
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.

Well, the trouble is, he has a smaller rim and much lower air resistance;
just as tandems have this problem with twice the weight behind normal air
resistance.

The OP might want to read Santana's disc testing experiences before
assuming they are the answer; I don't suppose it's feasble to fit a drum
brake...

And some drums can be just as bad about fading when hot, anyway.

Brake selection for a high-load or high-heat appliaction needs to be
done based on actual capabilities and limitations of the specific
unit. Assuming that a given design category's members are all
acceptable solutions is a recipe for failure.
--
Typoes are a feature, not a bug.
Some gardening required to reply via email.
Words processed in a facility that contains nuts.

jim beam said:

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.

Indeed. As a lawyer and a mountain bike who has been using disc
brakes for years, I'm wondering where all the huge lawsuits are,
holding everybody from the manufacturer to the local bike shops liable
for zillions for all the catastrophic injuries resulting from this
dire "problem." Not to mention the rush for the manufacturers to
change the brake caliper design to prevent it.

--dt

Ben Pearre said:

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

What usually occurs is that the tire blows off the rim unless the tire
is inflated far below the design limit. This occurs more often on
road bicycles and especially tandems.

I believe other parts fail before inner tubes "melt". Butyl rubber
can withstand high temperatures.

Jobst Brandt

Were is the hatrack said:

ISTR that even on larger rims, heat buildup on long, steep descents
is known to be able to induce blowouts, though I don't recall what
the exact mechanism of failure was determined to be. I believe that
Jobst Brandt had some testing planned to try to gather hard data.

I am relying on a friend to produce the circuit board that will feed
thermocouple information to the data recorder. Other parts of this
experiment are completed and lying on my desk.

Jobst Brandt

Rick said:

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.

RMNP Trail Ridge Road. Not the descent, so much, as all the RV traffic
going 20 mph. There's often no choice but to ride the brakes all the
way down.

RFM

Doug Taylor said:

jim beam said:

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.

Indeed. As a lawyer and a mountain bike who has been using disc
brakes for years, I'm wondering where all the huge lawsuits are,
holding everybody from the manufacturer to the local bike shops liable
for zillions for all the catastrophic injuries resulting from this
dire "problem." Not to mention the rush for the manufacturers to
change the brake caliper design to prevent it.

--dt

"but, but, but, caliper/dropout redesign would be admission of
culpability..." or so the consiracy theorists would argue.

Quoting Werehatrack <[email hidden]>:

Quoted message said:

Quoted message said:

The OP might want to read Santana's disc testing experiences before
assuming they are the answer; I don't suppose it's feasble to fit a drum
brake...

And some drums can be just as bad about fading when hot, anyway.

The problems Santana had with most discs were not fading. The problems
they had were bits melting, catching fire, warping, or falling off.
--
David Damerell <[email hidden]> flcl?
Today is Oneiros, September.

jim beam said:

frank, with respect, you're ignoring the elephant in the room. again.
there are countless examples of "better design" that are never adopted
in practice because they are not needed. left hand threaded lug nuts on
the left side of cars is absolutely a relevant example of what's not
necessary. just like redesigned fork dropouts on disk braked bikes.

Actually, left hand threaded lugnuts on cars *were* universally accepted,
*until a better solution came along* that allowed right hand thread while
still having the benefits of not unscrewing under precession.

*Really* bad example, in other words.

Jasper

jim beam said:

Doug Taylor wrote:

Quoted message said:

Quoted message said:

Indeed. As a lawyer and a mountain bike who has been using disc
brakes for years, I'm wondering where all the huge lawsuits are,
holding everybody from the manufacturer to the local bike shops liable
for zillions for all the catastrophic injuries resulting from this
dire "problem." Not to mention the rush for the manufacturers to
change the brake caliper design to prevent it.

Quoted message said:

"but, but, but, caliper/dropout redesign would be admission of
culpability..." or so the consiracy theorists would argue.

How quickly did the Pinto get redesigned? And the Bridgestone tyres?

Jasper