CPSC judgement on disk brakes and QR forks

[Tim McNamara]

In article <[email protected]>, [email protected]
(Spider) wrote:

> Tim McNamara <[email protected]> wrote in message
> news:<[email protected]>...
> > In article <[email protected]>, [email protected] (Spider)
> > wrote:
> >
> > > Solid hypotheses and theories will withstand pointed questions. In fact, pointed questions can
> > > serve to bolster them. Those familiar with science understand this.
> >
> > Annan's hypothesis withstands such questions.
>
> Actually, it doesn't. It may fall on the basis of whether or not the QR unscrewing mechanism is
> repeatable, and *under what conditions.*

That part of the hypothesis is gaining support, as has been already discussed. That's not
surprising, since the dynamics of the unscrewing of the QR nut is consistent with well-known
principles. (Not, I hasten to add, that they were particularly well-known to me before this
discussion. I've been observing nuts and bolts coming loose for many years without knowing what
caused it).

> > The problem is that most of the "pointed questions" to date are not in fact questions but
> > instead are ad hominem attacks.
>
> This, of course, is unadulterated B.S. Nowhere have I attacked James, I have just asked questions
> where I see there to be holes or clarifications.

You're personalizing my comments and misconstruing them. I didn't say that you had engaged in ad
hominem nor was I commenting on any one person's behavior. There has been a lot of ad hominem
directed towards Annan and collaterally towards Jobst and myself. I don't really bother to track
who says what, it's not worth the energy. If you say you haven't engaged in this, I'll take your
word for it.

> This is not a personal thing, but a desire to really see what's going on here. I do not know yet
> how large a design compromise the vertical drop-out/rear-caliper disk brake set-up happens to be.

I'm not sure what you're referring to here. We're talking about the front brake. The standard
placement for the rear disk brake does not create problems. As far as design compromise, all that
has to be done is to move the caliper ahead of the fork leg, which will result in a retention force
rather than an ejection force. End of problem. It would cost no more to make a fork with that
mounting than the current design.

> > I suppose people don't like thinking they've been hoodwinked into spending a lot of money of a
> > faulty product, and irrationally they attack the person who has pointd out the flaw instead of
> > the manufacturer who failed to apply basic freshman-year engineering pronciples to the design.
>
> This is an interesting comment from a non-scientist. Tim, I am a research chemist, and understand
> experimental science quite well.

You're personalizing again. I'm also reasonably well-versed in science, experimental design,
statistics, etc. from my psych graduate school days. My knowledge is rusty to be sure, as I don't
use it on a daily basis. I read research reports frequently, but I don't do research myself.

> I know what is meant by "statistically representative sample" and "controlled experiments." So
> far, neither has been fully done in regards to this question.

I agree that there have not been double-blind, randomized sample, with a control, etc. experiments
done. They aren't necessary in this sort of problem.

> In any case, you may feel free to point out wherever I have attacked James personally because of
> the hypothesis. Feel free to look carefully, but if I were you, I wouldn't waste more than an hour
> or so trying to find something, because it's just not there. This line of logic is what's known as
> a strawman argument.

Umm, you're the one setting up a straw man in this case, by misinterpreting what I've written in a
personal manner reflecting upon yourself. You say you have not engaged in personal attacks, and I
have not accused you of such.

> > The defensiveness and obtuseness has come from those people unwilling to perceive the situation
> > for what it is.
>
> An ad hominem attack? Weren't you just saying something about that?

You're personalizing again. Do we have that part clear, so that we can go on with a (hopefully)
fruitful discussion?

 

[Tim McNamara]

In article <f694b.33109$cj1.842@fed1read06>,
"Mike S." <mikeshaw2@coxDOTnet> wrote:

> If there's a serious design flaw, please post an exact count of how many people have been either
> injured or killed by this "design flaw" that CANNOT be traced to problems with the QR.

Ah, nice try. If you can't make sense, obfuscate.

> > How many failures are "significant?" Ten? Ten thousand? The design is faulty and, as such, one
> > failure is significant IMHO. It is not acceptable that the design puts an ejection force on the
> > front wheel. It's as simple as that.
>
> A statistical sample shows how many people with a real problem?

Every person using this equipment has the problem. The current design is flawed. It's really simple.

> Hell, I'll bet that you don't even ride a mtn bike with disc brakes!

You would win that bet. I've never bought a disk brake equipped bike because it's a silly design
that solves one problem: braking in deep mud. Since I actually care about the trail conditions
around where I live and want the trails to stay open, I don't ride in the mud. Hence I don't need
disk brakes which solve one problem and introduce several others.

 

[Super Slinky]

Tim McNamara said...

> It may come as a surprise to you that I do know this. However, the ejection force is easily
> estimated according to known engineering principles. The clamping force of the skewer is less
> easily estimated, but the limits are predictable. The ejection force has been shown to exceed the
> minimum clamping force required by CPSC rules. There is a well-known mechanism for loosening
> skewers, based on the mechanics of bolts, which increases the risk of the problem occurring.

Blah blah blah. If you are trying to impress me with techno-babble, you are barking up the wrong
tree. I don't know what your background is, but I do have a hard science degree (chemistry). I have
a better math education than most engineers and most of the physics. I know enough about these
simplified force models to be unimpressed with them. I doubt that a thorough investigation of all
the forces involved has ever been done. It would probably be good fodder for a graduate level
research paper. It is quite beyond the scope of a usenet discussion and just so much hot air.

> It is a problem caused usually by incorrect installation: dry tapers, dry threads, improper
> seating of the crank on the spindle, and inadequate torque on the bolt.

Yet you say that loosening QRs, a much rarer problem, is mistakenly attributed to incorrect
installation too often. Glaring inconsistency noted.

> Most people do stop and tighten their QRs, though- at the start of every ride after they've
> driven their bike to the trailhead. As has been pointed out, most rides may be of insufficient
> duration for the problem to advance to the point that the wheel can be ejected. Few people ever
> test the equipment to its limits, after all, although most riders like to think that they do on a
> regular basis.

I haven't touched my QRs in weeks. I only do so when I have occasion to remove the wheel. I suppose
I should check them more often just as a safety issue, but it has always been, and continues to be,
not a problem.

> We actually did need someone to tell us about it to prevent misattribution of cause and effect.
> Otherwise bicyclists would continue to blame user error as the cause of the wheel being ejected,
> misapplying the standard lore of QRs to a situation that is different than any other in this
> regard. On a bike with rim brakes, there is no ejection force on the wheel. On a bike with disk
> brakes, there is an ehection force. That changes the situation dramatically, and it is a
> significant design flaw even if millions of disk brake users never lose their wheels.
>
> Maybe only a few hundred people lose their front wheels because of this ejection force. One
> quadraplegia, one death is too many given that the problem is remediable by a simple design
> change. I am not willing to be blase about people getting injured or killed due to bad product
> design, although it is a typical American attitude to talk about "acceptable losses" in the name
> of "progress." We believe we control our destinies and that if somebody gets hurt, it must be
> their own damned fault. Unfortunately, this type of thinking is delusional.

I would be with you here if there were any indication that these hundreds of cases exist. James
Annan lost his front wheel on a tandem of all things. This is a special case, to put it nicely. You
hang out in
r.b.t. Surely you know that tandems require special consideration in terms of strength of parts to
ensure safe operation. The forces applied to the fork during braking would be much greater
than a one person bike. Use those force models to help show you why this is the case. The
other famous Missy Giove example involved a professional downhiller doing 'goofy stuff' on
one of the lightest, flexiest race specific XC forks on the market, and she didn't even lose
her wheel. Other anecdotes have been so vague as to be vaporous. Meanwhile, I hang out in
alt.mountain- bike and scour the Net for mountain bike information, and I have yet to see any
mention of this problem. You can believe what you want to believe, but I am quite convinced
that I have more immediate things to worry about.

 

[Mike S.]

<[email protected]> wrote in message news:[email protected]...
> Tim McNamara writes:
>
> > How many failures are "significant?" Ten? Ten thousand? The design is faulty and, as such, one
> > failure is significant IMHO. It is not acceptable that the design puts an ejection force on the
> > front wheel. It's as simple as that.
>
> Make that:
>
> "It is not acceptable that the design 'gratuitously' puts an ejection force on the front wheel."
> because this force could easily be a retention force by positioning the brake caliper forward of
> the fork. This is the basic error in the design, and proves that brake reaction forces were not
> considered by fork designers.
>

Actually, I'd think that it was the brake companies that designed the system first, the fork guys
just made what the brake companies wanted them to make. I could be wrong, but that's what I think
happened. That the fork manufacturers didn't take the time to see if the system was 100% perfect
is a given.

> Some contributors have stated that disengagement can occur only when the QR is not tight
> enough. How tight is "enough" and how can this be defined for the person buying such a bicycle?
> I find this proposal ridiculously irresponsible, and one that would not be seen favorably by
> any court of law.
>

> Jobst Brandt [email protected] Palo Alto CA

 

[Mike S.]

> If there's a serious design flaw, please post an exact count of how
> > many people have been either injured or killed by this "design flaw" that CANNOT be traced to
> > problems with the QR.
>
> Ah, nice try. If you can't make sense, obfuscate.

Not at all. You're telling me that there's a problem in the system. I want to know which part: if
its QR related, it goes in category A, etc.

The problem is that no one can tell me what percentage of the actual occurences of wheels ejecting
from the dropouts occured with a perfectly functioning QR.
>
> > > How many failures are "significant?" Ten? Ten thousand? The design is faulty and, as such, one
> > > failure is significant IMHO. It is not acceptable that the design puts an ejection force on
> > > the front wheel. It's as simple as that.
> >
> > A statistical sample shows how many people with a real problem?
>
> Every person using this equipment has the problem. The current design is flawed. It's
> really simple.
>
If there's so many people with this problem, why aren't wheels being ejected every day? From what
y'all are saying, it seems that the occurence of this problem should be an almost daily occurence.
For the statistical sample of mtn bikers riding discs, there HAS to be some idiot that doesn't do up
his/her QR right, or it breaks, or... That there have been what? 2-3 cases WORLDWIDE, means that
someone is overstating things.

If I'm incorrect on the # of cases, please correct me.

> > Hell, I'll bet that you don't even ride a mtn bike with disc brakes!
>
> You would win that bet. I've never bought a disk brake equipped bike because it's a silly design
> that solves one problem: braking in deep mud. Since I actually care about the trail conditions
> around where I live and want the trails to stay open, I don't ride in the mud. Hence I don't need
> disk brakes which solve one problem and introduce several others.

Since your mind is closed to the idea of riding discs, I won't even begin to explain the benefits.
I'll let you know my subjective opinion of my new XTR V-brakes on the "new" Dean I'm riding since I
sold the F3000 yesterday. If the Dean had disc mounts, they'd be on in a heartbeat, but it doesn't
so I'm stuck with V-brakes.

Mike

 

[Jobst Brandt]

Mike Shaw writes:

>>> How many failures are "significant?" Ten? Ten thousand? The design is faulty and, as such, one
>>> failure is significant IMHO. It is not acceptable that the design puts an ejection force on the
>>> front wheel. It's as simple as that.

>> Make that:

>> "It is not acceptable that the design 'gratuitously' puts an ejection force on the front wheel."
>> because this force could easily be a retention force by positioning the brake caliper forward of
>> the fork. This is the basic error in the design, and proves that brake reaction forces were not
>> considered by fork designers.

> Actually, I'd think that it was the brake companies that designed the system first, the fork guys
> just made what the brake companies wanted them to make. I could be wrong, but that's what I think
> happened. That the fork manufacturers didn't take the time to see if the system was 100% perfect
> is a given.

You may think that but the brakes existed long before they were applied to mountain bikes and just
as the brake pad manufacturer is not responsible for fork attachment, so is the disk and caliper
manufacturer not responsible for that. These are OEM components that the fork manufacturer
integrates into a bicycle. He and the bicycle manufacturer are responsible for offering a safe
mechanism.

>> Some contributors have stated that disengagement can occur only when the QR is not tight enough.
>> How tight is "enough" and how can this be defined for the person buying such a bicycle? I find
>> this proposal ridiculously irresponsible, and one that would not be seen favorably by any court
>> of law.

Yes?

Jobst Brandt [email protected] Palo Alto CA

 

[Doug Taylor]

"Joe Riel" <[email protected]> wrote in message news:[email protected]...

>
> So your position is no longer that the problem should be nipped in the
bud,
> but rather wait until damage awards have been issued? Do you think it would have been better for
> Ford to do something as soon as they knew about the problem?

This response begs the question, which is, of course, IS there a problem? If there IS a problem, and
if it is significant, of course it is the interst of everyone, bicycle industry to consumer, to nip
it in the bud. Industry, to avoid financial ruin; consumer to avoid injury.

To date, I reiterate, the industry, apparently, has not found a problem; the following, apparently,
have not occured: 1) irrefutable proof of the premise (that disc brakes cause front wheel
ejection); 2) statiscally significant evidence of injury caused by front wheel ejection justifying
a warning or recall.

Until either of those two occur, it is not cost effective to recall all forks and disc brakes. That
would be financially ruinous in itself.

> > It's a gamble and time will tell. Three possibilities: 1) nothing will happen or change and
> > discs/forks will continue to be made as they are
now;
> > 2) old equipment will not be recalled, but new equipment will be altered "just in case;" 3)
> > Numerous lawsuits will be filed, huge damage awards rendered, old equipment recalled, new
> > equipment altered.
>
> >
> > I'm betting on 1 or 2. If 3 occurs, I'll publically eat crow. If 3
doesn't
> > occur, I'll expect the Annan, Brandt McNamara crowd publically to eat
crow.
>
> > Fair enough?
>
> Hardly. James et al are not hoping that 3 occurs, not as far as I can
tell.

Actually, there is a 4th possibilty, which I assume would be the Annan position: prove the
premise, recall the offending equipment, and change the design, BEFORE the grievous injuries and
big lawsuits.

> If there isn't a problem---as you appear to be saying---why is 2 a win for you? Of course, no one
> "wins" in this game...

2 is the best for the bicycle industry, if there is a problem (1 assumes no problem), reasoning
as follows:

There is evidence that disc brakes, in some circumstances, DO cause front wheel ejection.
Thankfully, it requires a "perfect storm" of events to coincide before it can occur, and therefore
does not occur frequently when viewed against the total number of disc brake equipped bicycles in
use. Consequently, exisiting reserves will pay for any liability suits that may arise from use of
exisitng equipment; there is no need to recall it. New equipment will then be designed to eliminate
the "perfect storm" event. The industry survives. A few unlucky individuals lose. Such is life in
any physical activity as potentially dangerous as off-road cycling.

 

[Joe Riel]

Super Slinky <[email protected]> writes:

> I know enough about these simplified force models to be unimpressed with them.

If you see a technical problem with the analysis, please point it out.

Engineering is a practical/applied science. In a complicated design it is not possible to ascertain
every possible failure mode and rigorously analyze it. Rather, general principles are followed and,
when appropriate, shown to be applicable through testing. Margin is built into the design.

In the case involved, it is easily shown that the ejection force applied to the wheel exceeds the
design limits of the quick release. As such, any reasonable engineer would reject that design as
flawed. That is, if this had been noted in the design phase of a reputable company, the design would
never have made it to the testing phase, let alone the market.

Given that a failure [wheel ejection] will almost certainly injure the rider, the onus must be on
the manufacturers to demonstrate that the design is safe. They cannot point to the paucity of field
failures as evidence. Try getting that one by a standards agency!

> I would be with you here if there were any indication that these hundreds of cases exist.

Have you ever had to work with a safety agency to approve a design? Or resubmit when a
failure occurred?

> James Annan lost his front wheel on a tandem of all things. This is a special case, to put
> it nicely.

Are you suggesting that proper design should not take into account such special cases?

Shifting gears slightly, here's something that all parties might consider.

The *average* upward force on the wheel during riding is significantly less tha the peak downward
[ejection] force applied during hard braking. Given that the fork has shock absorbers, the *peak*
upward force may also be significantly less than the ejection force. As such, one reason that the
typical skewer may not unscrew is that there isn't enough upwards force to move the wheel back up
the dropout. That can be crudely and safelly tested on a MTB with front shocks and a rim brake by
clamping the quick release so that there is a small gap between the skewer and the end of the slot,
riding the bike, and rechecking it later.

Joe Riel

 

[Super Slinky]

Joe Riel said...

> Engineering is a practical/applied science. In a complicated design it is not possible to
> ascertain every possible failure mode and rigorously analyze it. Rather, general principles are
> followed and, when appropriate, shown to be applicable through testing. Margin is built into
> the design.

Thank you for repeating what I said in different words. I said, 'I doubt that a thorough
investigation of all the forces involved has ever been done.'

> In the case involved, it is easily shown that the ejection force applied to the wheel exceeds the
> design limits of the quick release. As such, any reasonable engineer would reject that design as
> flawed. That is, if this had been noted in the design phase of a reputable company, the design
> would never have made it to the testing phase, let alone the market.

Oh, really. Now where might I find the design limits of say a Salsa QR when used with a suspension
fork that has magnesium lower legs? Or am I just supposed to take your word for it? I strongly doubt
that anyone knows what they are, because as you say engineering is an applied science and the vast
majority of bicycle designs have almost certainly came about by trial and error rather than
mathematical modeling.

> Given that a failure [wheel ejection] will almost certainly injure the rider, the onus must be on
> the manufacturers to demonstrate that the design is safe. They cannot point to the paucity of
> field failures as evidence.

A bizarre statement. I can't think of a better way to justify a design than thousands of consumers
using a product under severe conditions and an almost complete lack of failures. Evidently, the
CPSC concurs.

> Try getting that one by a standards agency!

Certification by a standards agency isn't mandatory and if it doesn't help to sell the product, why
would a manufacturer pay for it? Since these alleged failures are so rare, why would a consumer look
for the reassurance of a certification?

> Have you ever had to work with a safety agency to approve a design? Or resubmit when a failure
> occurred?

I work for the most recognizable safety agency in the world and I have designed several chemical
tests that are certified in 48 states. Our customers include the armed forces, municipal governments
and many corporations, some of which are household names. I am audited several times a year and we
discuss and resubmit minor changes to our procedures on an almost daily basis.

> Are you suggesting that proper design should not take into account such special cases?

That's exactly what I'm suggesting, because, you, like everyone else on this crusade repeatedly
ignores the fact that the QR and vertical dropout design is not the only one available. The problem
is with the bike maker choosing this design. All James Annan proved is that maybe this design
doesn't belong on a tandem, just like low spoke count rims don't belong on them.

> Shifting gears slightly, here's something that all parties might consider.
>
> The *average* upward force on the wheel during riding is significantly less tha the peak downward
> [ejection] force applied during hard braking. Given that the fork has shock absorbers, the *peak*
> upward force may also be significantly less than the ejection force. As such, one reason that the
> typical skewer may not unscrew is that there isn't enough upwards force to move the wheel back up
> the dropout. That can be crudely and safelly tested on a MTB with front shocks and a rim brake by
> clamping the quick release so that there is a small gap between the skewer and the end of the
> slot, riding the bike, and rechecking it later.

Balderdash. The wheel isn't going to move much at all until the skewer is loose enough to get past
the lawyer lips. The QR fits snugly inside the lawyer lips and your little test is impossible to do
while they are intact. But thanks for demonstrating that you are yet another person passing
judgement on this subject when you clearly don't know the first thing about it.

 

[Joe Riel]

Super Slinky <[email protected]> writes:

> Oh, really. Now where might I find the design limits of say a Salsa QR when used with a suspension
> fork that has magnesium lower legs? Or am I just supposed to take your word for it?

ISO Technical Commitee 149 wrote a standard for quick-release retention force. I do not know the
current requirement. In the early 90's it was 517 lbs with a 30 lb lever clamping force.

Joe Riel

 

[Jobst Brandt]

Mike Shaw writes:

>> OK. How about a simple experiment, assuming you have access to a disk brake equipped bicycle.
>> Since retention ridges are only on the outside of the fork dropout, remove the QR skewer and
>> perform a static braking test by pushing the bicycle forward with the brake applied. You could
>> also do this at low speed without hazard. Then report whether this disengages the wheel or not.

>> This is intended to demonstrate that there is a separating force, something that has been argued
>> here at length.

> Yeah, and I'll bet that if you did the same with cantis or V-brakes, it'd do the same thing. Since
> I haven't tried it, I don't know. Anyone willing to try?

This response probably wraps up the nature of this discussion the better than any yet offered. I get
the impression that others who defend the status quo also fall into this category level of
mechanical skills. To believe that a rim brake at the fork crown can causes a wheel ejection force
similar to that of the disc brake under discussion, shows beyond any doubt that the mechanics and
dynamics of braking are not understood. It shows an ignorance of forces and their reactions.

That the test was performed at all in order to determine whether there is a separating force,
underscores this lack of understanding and puts those who think there is no problem in the position
of arguing about something they do not understand; while ridicule those that do.

Jobst Brandt [email protected] Palo Alto CA

 

[Jobst Brandt]

Mike Shaw writes:

>> OK. How about a simple experiment, assuming you have access to a disk brake equipped bicycle.
>> Since retention ridges are only on the outside of the fork dropout, remove the QR skewer and
>> perform a static braking test by pushing the bicycle forward with the brake applied. You could
>> also do this at low speed without hazard. Then report whether this disengages the wheel or not.

>> This is intended to demonstrate that there is a separating force, something that has been argued
>> here at length.

> Yeah, and I'll bet that if you did the same with cantis or V-brakes, it'd do the same thing. Since
> I haven't tried it, I don't know. Anyone willing to try?

This response probably wraps up the nature of this discussion better than any yet offered. I get the
impression that others who defend the status quo also fall into this level of mechanical skills.

To believe that a rim brake at, the fork crown, can causes a wheel ejection force similar to that of
the disc brake under discussion, shows beyond any doubt that the mechanics and dynamics of braking
are not understood. It shows an ignorance of forces and their reactions.

That the test was performed at all, in order to determine whether there is a separating force,
underscores this lack of understanding and puts those who think there is no problem in the position
of arguing about something they do not understand; while ridicule those that do.

Jobst Brandt [email protected] Palo Alto CA

 

[Tim McNamara]

In article <[email protected]>,
"Doug Taylor" <[email protected]> wrote:

> "Joe Riel" <[email protected]> wrote in message news:[email protected]...
>
> >
> > So your position is no longer that the problem should be nipped in the bud, but rather wait
> > until damage awards have been issued? Do you think it would have been better for Ford to do
> > something as soon as they knew about the problem?
>
> This response begs the question, which is, of course, IS there a problem? If there IS a problem,
> and if it is significant, of course it is the interst of everyone, bicycle industry to consumer,
> to nip it in the bud. Industry, to avoid financial ruin; consumer to avoid injury.

Well, there clearly is a problem: disk brakes result in an ejection force on the front wheel. That
question has been answered.

Is the problem significant? Define "significant." Do 100 people need to be injured, paralyzed or
killed per year for the problem to be considered "significant?" What's the threshhold of
acceptable losses?

> To date, I reiterate, the industry, apparently, has not found a problem; the following,
> apparently, have not occured: 1) irrefutable proof of the premise (that disc brakes cause front
> wheel ejection); 2) statiscally significant evidence of injury caused by front wheel ejection
> justifying a warning or recall.

What is "statistically significant?" And are you willing to be one of the statistically
insignificant victims of a bad design, maybe spending the rest of your life in a wheelchair, because
someone like you didn't think the risk was "significant" enough to fix the problem and prevent any
possibility of the problem occurring? I think that one injury or death due to faulty design is above
the threshhold of significance. People and their lives are more important. I realize that's an
unfashionable viewpoint in today's Wall Street driven world.

Herein lies the rub. The industry can't find the problem, because finding it would be to admit they
didn't do their design homework. It would be an admission of negligence that would open them up to
individual and class action litigation. Of course, now that the problem is publicly known they are
ethically obligated to examine the design issue, which is straightforward enough actually. It
rapidly becomes a tiny version of the Big Tobacco problems, especially if the industry handles it
with the same mindset that Big Tobacco used.

Personally, I see the situation as being very clear and the path forward as being very simple.
Acknowledge the problem and make changes to new designs to prevent it. Offer an adapter kit to
correct the problem on existing forks, for those who wish to utilize it, under a general recall.
This should minimize the financial costs to the industry.

 

[Tim McNamara]

In article <[email protected]>, Super Slinky
<[email protected]> wrote:

> Tim McNamara said...
>
> > It may come as a surprise to you that I do know this. However, the ejection force is easily
> > estimated according to known engineering principles. The clamping force of the skewer is less
> > easily estimated, but the limits are predictable. The ejection force has been shown to exceed
> > the minimum clamping force required by CPSC rules. There is a well-known mechanism for loosening
> > skewers, based on the mechanics of bolts, which increases the risk of the problem occurring.
>
> Blah blah blah. If you are trying to impress me with techno-babble, you are barking up the wrong
> tree. I don't know what your background is, but I do have a hard science degree (chemistry). I
> have a better math education than most engineers and most of the physics.

Done bragging? Should we talk about the size of our dicks now?

> I know enough about these simplified force models to be unimpressed with them. I doubt that a
> thorough investigation of all the forces involved has ever been done. It would probably be good
> fodder for a graduate level research paper. It is quite beyond the scope of a usenet discussion
> and just so much hot air.

It would be an excellent research paper topic. However, I think that you may be conceptually
overcomplicating the forces involved.

> > It is a problem caused usually by incorrect installation: dry tapers, dry threads, improper
> > seating of the crank on the spindle, and inadequate torque on the bolt.
>
> Yet you say that loosening QRs, a much rarer problem, is mistakenly attributed to incorrect
> installation too often. Glaring inconsistency noted.

This is not what I said. See below. If you're going to contradict me, at least have the intellectual
honesty to accurately represent my position.

> > We actually did need someone to tell us about it to prevent misattribution of cause and effect.
> > Otherwise bicyclists would continue to blame user error as the cause of the wheel being ejected,
> > misapplying the standard lore of QRs to a situation that is different than any other in this
> > regard. On a bike with rim brakes, there is no ejection force on the wheel. On a bike with disk
> > brakes, there is an ehection force. That changes the situation dramatically, and it is a
> > significant design flaw even if millions of disk brake users never lose their wheels.

 

[Tim McNamara]

In article <[email protected]>, Super Slinky
<[email protected]> wrote:

> That's exactly what I'm suggesting, because, you, like everyone else on this crusade repeatedly
> ignores the fact that the QR and vertical dropout design is not the only one available. The
> problem is with the bike maker choosing this design.

That's exactly what Annan has been saying all along.

> But thanks for demonstrating that you are yet another person passing judgement on this subject
> when you clearly don't know the first thing about it.

And your mechanical engineering degree is from which institution? Isn't this the pot calling the
kettle black?

 

[Tim McNamara]

In article <1zf4b.33303$cj1.741@fed1read06>,
"Mike S." <mikeshaw2@coxDOTnet> wrote:

> Actually, I'd think that it was the brake companies that designed the system first, the fork guys
> just made what the brake companies wanted them to make. I could be wrong, but that's what I think
> happened. That the fork manufacturers didn't take the time to see if the system was 100% perfect
> is a given.

That seems quite plausible. It still leaves us with the faulty design, however.

 

[Super Slinky]

[email protected] said...

> This response probably wraps up the nature of this discussion the better than any yet offered. I
> get the impression that others who defend the status quo also fall into this category level of
> mechanical skills. To believe that a rim brake at the fork crown can causes a wheel ejection force
> similar to that of the disc brake under discussion, shows beyond any doubt that the mechanics and
> dynamics of braking are not understood. It shows an ignorance of forces and their reactions.
>
> That the test was performed at all in order to determine whether there is a separating force,
> underscores this lack of understanding and puts those who think there is no problem in the
> position of arguing about something they do not understand; while ridicule those that do.

Well, you would be wrong if you passed that judgement against me. My mechanical skills are just
fine, thank you. I never argued that there wasn't a unique force applied to the QR from disc brakes.
Still, I remain unimpressed by your techno-babble. I have done my time with force models, but
fortunately I am under no obligation to try and account for every force working on a QR on pencil
and paper or to dissect your selective arguments. I have neither the time nor the incentive to do
so. I choose to remain content in the knowledge the the real world reports that no problem exists.
This self-evident fact should be a clue to you that you are missing something. Why you continue to
insist that there is a problem when there are so very few, if any, reports of it only you can
explain. According to better engineers than you, bumble bees shouldn't be able to fly. So even if it
should turn out that on paper wheels should be popping out on every ride, we who use them know that
they do not. I find it hypocritical that you attack those who don't agree with you as being too
stupid to understand when most of you who say that disc brakes and QRs are such a dire threat don't
use them. You don't, Tim McNamara doesn't, Joe Riel doesn't. When the earlier threads were cross-
posted to the dedicated mountain bikers on alt.mountain-bike, it generated about as much interest as
a streaker in a nudist colony. Apparently the only people who think you have a point is about a half
dozen roadies in r.b.t.

 

[Joe Riel]

Super Slinky <[email protected]> writes:

> Balderdash. The wheel isn't going to move much at all until the skewer is loose enough to get past
> the lawyer lips. The QR fits snugly inside the lawyer lips and your little test is impossible to
> do while they are intact.

Have you tried it? On the two forks I have with laywer lips there is enough slop to move the quick
release down so that it is not contacting the top of the drop out.

Joe Riel

 

[Doug Taylor]

"Tim McNamara" <[email protected]> wrote in message news:timmcn->

> Is the problem significant? Define "significant." Do 100 people need to be injured, paralyzed or
> killed per year for the problem to be considered "significant?" What's the threshhold of
> acceptable losses?

It is not up to me, some geek on usenet, to define "significant;" it is up to the manufacturers who
sell the equipment and who will pay the damages if they are found liable for a defective product. To
them, it is simple cost-benefit analysis: "significant" is the point at which it would cost more to
leave the product as it is, than recall it and change the design.

As other posters have noted, the alleged "fact" that discs make QR's fail and cause front wheel
ejection has not been observed in practice to any noticeable extent (you only hear of it on
rec.bicycles.tech; not alt.mountain-bike; not the bike mags; not the newspapers; not in the trial
lawyers' newsletter; not among people who ride or race mountain bikes, etc.) let only any
"significant" extent that would cause the bike industry to change anything.

As for you, please supply the name, date and place for *any* cyclist who has been severly injured,
paralyzed or killed due to your pet problem. Bet you can't find one.

 

[Terry Morse]

Doug Taylor wrote:

> As for you, please supply the name, date and place for *any* cyclist who has been severly injured,
> paralyzed or killed due to your pet problem. Bet you can't find one.

You'd make a great manager at NASA.

"Design problem? What design problem?"
--
terry morse Palo Alto, CA http://www.terrymorse.com/bike/