CPSC judgement on disk brakes and QR forks

[Mike S.]

"James Annan" <[email protected]> wrote in message news:[email protected]...
> Mike S. wrote:
> > . Further independent testing and examination
> >
> >>has verified- in a preliminary fashion at least- both the ejection force and the loosening
> >>of QRs.
> >>
> >
> > When was the last time a QR came undone spontaneously? Snagged on
trees,
> > bushes, bashed on rocks, yes. Loosen completely on its own? Hmmm...
don't
> > think so.
>
> I received this by email recently, from a shop owner who was setting up a bike for a customer:
>
> "Well, just in the parking lot, the disc will demonstrably begin to pull the wheel out of the drop
> out. A few on-off cycles of braking and the nut can be seen backing off, if you keep it up, the QR
> is loose enough to clear the lawyer tabs in just a minute of this action, mind you just in the
> parking lot."
>
> I guess that particular parking lot has more than its fair share of rocks and bushes to snag the
> lever on.
>
> Ben Cooper is another shop owner who has done similar tests and found a correctly fastened skewer
> loosening repeatedly under very light use. If you massively overtighten the skewer, as many MTBers
> have learnt by experience to do, you can reduce the likelihood of this occurring but there is no
> way of knowing in advance how tight is tight enough, nor how much this overtensioning increases
> the likelihood of snapping the skewer, another `operator error' that can have very serious
> consequences.
>
> James
>
Now, if I were to go to any of the shops here in San Diego, grab a bike off the rack, roll it out,
and test it, chances are I'll find that the QR probably isn't going to move. Just like people can
quote the Bible to say pretty well whatever they want, a few "tests" being quoted doesn't a
scientific paper make.

In the years that I've been riding discs, I have not one time, I say again, NOT ONE TIME, have had a
QR either come loose, or the wheel move in the dropouts. Am I extremely cautious? Nope. Am I riding
DH? No to that one too. Am I a competent to tighten a QR without supervision? I guess so.

I don't dispute that there's something going on, but it seems to me that the current setup is
adequate for the majority of riders. That there are a few failures out there doesn't surprise me.
Given a big enough statistical sample, there's going to be a failure in anything.

So, to answer Jobst here, yes I believe that the current setup is adequate. Is it perfect? God no.
Could the interface be better designed? Probably. Do I think it will be? Probably not any time soon.

So, all you that believe that there's an inherent problem in the design, what is the proposition for
fixing the situation? Remember that this design has to work with conventional wheels.

Mike

 

[Tim McNamara]

In article <sQN3b.32234$cj1.10026@fed1read06>, "Mike S." <mikeshaw2@coxDOTnet> wrote:

> . Further independent testing and examination
> > has verified- in a preliminary fashion at least- both the ejection force and the loosening
> > of QRs.
> >
> When was the last time a QR came undone spontaneously? Snagged on trees, bushes, bashed on rocks,
> yes. Loosen completely on its own? Hmmm... don't think so.

Again, like the rest of the Annan-bashers, you've chosen to avoid reality. Loosening QR with front
disk brakes has been demonstrated in an article published in the bike industry press in response
to Annan's Web site. I've posted an URL where you can read the article on three occasions in the
past 8 weeks.

> I just did the test that Jobst recommended and indeed, my disc equipped wheel migrated back and
> down when there was no clamping pressure applied by the QR. However, once there was pressure
> applied by the QR, this tendency was overcome.

Overcome in terms of visible movement for the time being, you mean.

> Questions that just popped into my mind: Exactly how much force does it take to eject the wheel
> from a properly tightened QR/fork interface? How much force is a "typical" QR exerting? Exactly
> where is the tendency of the wheel to come out of the bottom of the fork equal to the clamping
> force of the QR? How much force is the disc brake exerting on the QR/fork interface?

Those things have already been estimated, Mike, and discussed ad nauseum. Where ya been?

 

[Mike S.]

"Tim McNamara" <[email protected]> wrote in message
news:[email protected]...
> In article <sQN3b.32234$cj1.10026@fed1read06>, "Mike S." <mikeshaw2@coxDOTnet> wrote:
>
> > . Further independent testing and examination
> > > has verified- in a preliminary fashion at least- both the ejection force and the loosening of
> > > QRs.
> > >
> > When was the last time a QR came undone spontaneously? Snagged on trees, bushes, bashed on
> > rocks, yes. Loosen completely on its own? Hmmm... don't think so.
>
> Again, like the rest of the Annan-bashers, you've chosen to avoid reality. Loosening QR with front
> disk brakes has been demonstrated in an article published in the bike industry press in response
> to Annan's Web site. I've posted an URL where you can read the article on three occasions in the
> past 8 weeks.
>
> > I just did the test that Jobst recommended and indeed, my disc equipped wheel migrated back and
> > down when there was no clamping pressure applied by the QR. However, once there was pressure
> > applied by the QR, this tendency was overcome.
>
> Overcome in terms of visible movement for the time being, you mean.
>
> > Questions that just popped into my mind: Exactly how much force does it take to eject the wheel
> > from a properly tightened QR/fork interface? How much force is a "typical" QR exerting? Exactly
> > where is the tendency of the wheel to come out of the bottom of the fork equal to the clamping
> > force of the QR? How much force is the disc brake exerting on the QR/fork interface?
>
> Those things have already been estimated, Mike, and discussed ad nauseum. Where ya been?

Watching "the disc brake/QR is faulty" crowd bash it out with the "there's no problem crowd" and
laughing at everyone. I fall firmly into the "there's no real problem" crowd till proven
conclusively that there's a significant occurrence of failures. This is especially true since I
actually mtn bike on a bike with discs, unlike some of the "its the design" crowd.

I just went out and examined my dropouts. You'd think with the prevalence of the problem we're
talking about, that there'd be scores where the axle/QR was moving around. Nothing other than the
normal imprint from attaching the wheel (in one spot) and there's no scoring on the lawyer lips from
the wheel partially ejected. I don't overtighten my QR, so please explain to me why there's a
problem again...

Mike

 

[Joe Riel]

Doug Taylor <[email protected]> writes:

> Forget the fact that if it were true, it would be in the interest of the CPSC and the cycling
> industry to nip it in the bud, BEFORE the tort lawyers blow the whole thing to holy hell.

Like Ford nipped the Explorer/Pinto problems in the bud?

> And that only a tiny minority of cyclists have been injured by this problem, IF it's a problem and
> IF the problem caused the injury.

What percentage of said Ford owners had problems? A tiny minority, perhaps? How is this different?

Joe Riel

 

[Spider]

Tim McNamara <[email protected]> wrote in message
news:<[email protected]>...
> In article <PrL3b.32217$cj1.11028@fed1read06>, "Mike S." <mikeshaw2@coxDOTnet> wrote:
>
> > <[email protected]> wrote in message
> > news:[email protected]...
> >
> > > 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?
>
> Umm, it's been done. It's been written up in this newsgroup.
>
> > I've got an F3000 out in the garage that I can experiment with in a bit. I'll let you know what
> > happens.
>
> Please do. Having checked this out personally, I can tell you what you will find. The wheel will
> stay in the dropouts with caliper brakes, cantilever brakes and V brakes. The wheel will be pushed
> out of the dropout with disk brakes.

Yes, it will. What is the magnitude of the risk of this design compromise? ATM, unknown. Too many
independent parameters to judge at this point.

> This has been verified by informal testing by participants in this newsgroup, and has been
> verified by independent testing within the bike industry.

If you mean by the German group, no, that is not yet in the realm of "verification." Even they say
that more experiments need to be done, as per the article in STW.

> The reference for this has been posted several times, and it is entertaining to note that Annan's
> critics continue to be silent about this.

Wrong again. I pointed out that it was merely preliminary data, and not conclusive.

> The alleged hype and ego are now on the side of the people trying to argue against observable
> reality.

Here's where you folks get into trouble. "Observable reality" is often at odds with what is really
going on. That is why optical illusions exist. Controlled study is the final arbiter, not claims in
a newsgroup, nor self-selected, unknown-condition samples to a website.

> At this point in the discussion, sheer obstructionism or lack of simple comprehension seem to be
> the only explanations.

Another condescending dismissal. It reminds me of folks who are pro-war with regards to Iraq. When
they hear someone has questions, or is hesitant, they level their gaze and say "So, why do you
support Saddam?" or "you're unpatriotic."

Solid hypotheses and theories will withstand pointed questions. In fact, pointed questions can serve
to bolster them. Those familiar with science understand this.

If you can't answer the questions, say "I don't know." If you know the answer, post it or the link.
If you find the questions tiresome, don't bother responding. You (and the others) do yourself a
DISservice by being defensive and obtuse.

Spider

 

[Super Slinky]

Tim McNamara said...

> Oh ********. This is a problem of your interpretation, not a problem with what Annan published
> here and on his Web site. The rational response would have been to examine the analysis and the
> available evidence, which in turn would have brought you to the conclusion that Annan has a valid
> point. Further independent testing and examination has verified- in a preliminary fashion at
> least- both the ejection force and the loosening of QRs.

I agree with the ejection force part of the argument. I have done the experiment with loosening the
QR and applying the front disc. It most certainly does tend to twist the axle out of the dropout,
but then riding with a loose QR is likely to be hazardous to your health regardless of what type of
braking system one has. The big question revolves around whether or not this ejection force is a
cause for concern when set against a properly tightened QR, and that is where things get real
sketchy. You see, lots of parts on a bicycle are bolted together and have forces working against
them. Cranks are an excellent example and crank bolts work loose all the time for some unfortunate
people. It is a big problem. I have seen countless complaints from people who have to tighten their
cranks constantly, but I have yet to see someone complain that they must constantly stop to tighten
front QRs. If this was a common problem, then we wouldn't have needed James Annan to tell us about
it. I'm sorry I have to be the one to say the Emperor wears no clothes, but there just isn't a body
of evidence to back up this tempest in a teapot, hence the CPSC judgement.

 

[Tim McNamara]

In article <AuS3b.32715$cj1.4239@fed1read06>, "Mike S." <mikeshaw2@coxDOTnet> wrote:

> Watching "the disc brake/QR is faulty" crowd bash it out with the "there's no problem crowd" and
> laughing at everyone. I fall firmly into the "there's no real problem" crowd till proven
> conclusively that there's a significant occurrence of failures. This is especially true since I
> actually mtn bike on a bike with discs, unlike some of the "its the design" crowd.

Too bad you lack either the abiliy or the willingness to comprehend the fact that there is a serious
design flaw, and the fact that the flaw has been verified by independent researchers. It's really
very simple, and burying your head in the sand doesn't make the problem go away.

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.

> I just went out and examined my dropouts. You'd think with the prevalence of the problem we're
> talking about, that there'd be scores where the axle/QR was moving around. Nothing other than the
> normal imprint from attaching the wheel (in one spot) and there's no scoring on the lawyer lips
> from the wheel partially ejected. I don't overtighten my QR, so please explain to me why there's a
> problem again...

No. Why continue to waste my time on you? It's been explained.

 

[Chris Zacho "Th]

sounds like a "pass-off" to me.

May you have the wind at your back. And a really low gear for the hills! Chris

Chris'Z Corner "The Website for the Common Bicyclist": http://www.geocities.com/czcorner

 

[Tim McNamara]

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. The problem is that most of the "pointed questions" to
date are not in fact questions but instead are ad hominem attacks.

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
dynamic is well-known (see Ibsen's "Enemy of the People" for example).

> If you can't answer the questions, say "I don't know." If you know the answer, post it or the
> link. If you find the questions tiresome, don't bother responding. You (and the others) do
> yourself a DISservice by being defensive and obtuse.

There's nothing obtuse about the hypothesis. It's simple, straightforward and based on sound
engineering principles. The defensiveness and obtuseness has come from those people unwilling to
perceive the situation for what it is.

 

[Jose Rizal]

Tim McNamara:

> 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. The problem is that most of the "pointed questions"
> to date are not in fact questions but instead are ad hominem attacks.

You're now just being selective. There have been quite reasonable questions about the mechanism for
loosening QRs which have not been satisfactorily (quantitatively) answered, and in fact at least one
of the "references" pointed at for this (eg the German mob) has stated that more work is required.

> 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
> dynamic is well-known (see Ibsen's "Enemy of the People" for example).

You practice what you preach against. This is nothing more than a poor diversion. On the one hand
you have admitted before that the problem occurs on a fairly small sample of users, now you're
saying everyone with disc-equipped forks has been hoodwinked.

I've read your protestations against the questioners of the whole issue, but your arguments have
merely been the echoing of what others understand the problem to be. By your own admission your
background is in the non-engineering, soft sciences, yet you accuse others of failing to "apply
basic freshman-year engineering pronciples to the design". Without being insulting about it, have
you personally verified the calculations, applied the theory of the proposed underlying principles,
and made some quantitative analysis of your own?

> > If you can't answer the questions, say "I don't know." If you know the answer, post it or the
> > link. If you find the questions tiresome, don't bother responding. You (and the others) do
> > yourself a DISservice by being defensive and obtuse.
>
> There's nothing obtuse about the hypothesis. It's simple, straightforward and based on sound
> engineering principles.

There are in fact several hypotheses which need to occur simultaneously for a wheel to be ejected.
That there is a force trying to eject the wheel by using a disc brake is not in contention. What
still requires quantitative analysis and proof is the QR loosening hypothesis. That is, an
"adequately" tightened QR in a bicycle fork equipped with disc brakes. Don't lump this with the
wheel ejection force issue; these are distinctly separate issues. I don't contend that this latter
cannot happen: I contend that there is not enough proof that this is indeed what happens.

> The defensiveness and obtuseness has come from those people unwilling to perceive the situation
> for what it is.

While there have been exaggerated accusations and arguments on the "against" side, your blanket
assessment of the questions raised is just dismissing those legitimate technical questions asked of
the phenomenon, something which makes me think that you also suffer from what you accuse others of
being: unable to understand the "basic freshman engineering" principles of the questions involved.

 

[Super Slinky]

[email protected] (Chris Zacho "The Wheelman") said...

> sounds like a "pass-off" to me.
>
> May you have the wind at your back. And a really low gear for the hills! Chris

Or maybe they are just doing their job. Not every complaint warrants remedial action.

 

[Doug Taylor]

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

> What percentage of said Ford owners had problems? A tiny minority, perhaps? How is this different?

Uh, how about that in the case of the Pinto, as well as Firestone tires, people actually sustained
real and grievous injuries or death, the companies were actually sued, and huge damage awards
entered BEFORE there were any recalls. CSPC and the fork / disc manufacturers apparently have
reviewed the facts and didn't find a problem significant enough to warrant a recall or some type of
warning in the case of the alleged fork/disc malfunction. They apparently do not think there is
enough risk worth the expense of a recall or a design change.

They MAY be wrong - maybe there is a real problem and the tort lawyers will find some "good cases"
(death or severe injuries) to bring lawsuits, or even a number of cases to bring a class action,
THEN prove liability, and then the manufacturers will pay, recall old equipment, and change the
design of new equipment to correct the problem.

OTOH, maybe there is no problem or an insignificant risk, and they will save money in the long run
by keeping the status quo.

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?

 

[Jobst Brandt]

David Damerell writes:

>> How was the 0.6g decelleration figure arrived at? (This is one I've had a problem with from the
>> beginning - I don't know where to get a g-meter for my mtb. I would be willing to experiment if I
>> had one.)

> As was explained to you at the time, the maximum deceleration attainable without lifting the rear
> wheel on the flat is directly determined by the angle between the horizontal and a line drawn
> through the forward contact patch and the centre of gravity of the bike+rider.

That the 0.6g number entered the discussion is unfortunate, because it only ads confusion while
being valuable only in computing maximum disengagement force for a specific rider. One cannot
predict where riders will position their CG when braking hard, it depending on rider skill and
aggressiveness.

The important parameter is that the disengaging force is about three times the downward force when
skidding on solid ground. For pavement, where disk brakes are also used both on road bicycles and
MTB's the coefficient of friction is about one as can be seen from racing pictures with riders
leaning at about 45 degrees to the road surface. Brake disks are a small as 1/4 the wheel, giving a
4:1 force.

Jobst Brandt [email protected] Palo Alto CA

 

[Joe Riel]

"Doug Taylor" <[email protected]> writes:

> "Joe Riel" <[email protected]> wrote in message news:[email protected]...
>
> Uh, how about that in the case of the Pinto, as well as Firestone tires, people actually sustained
> real and grievous injuries or death, the companies were actually sued, and huge damage awards
> entered BEFORE there were any recalls.

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?

> 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. 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...

Joe Riel

 

[Tim McNamara]

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

> Tim McNamara said...
>
> > Oh ********. This is a problem of your interpretation, not a problem with what Annan published
> > here and on his Web site. The rational response would have been to examine the analysis and the
> > available evidence, which in turn would have brought you to the conclusion that Annan has a
> > valid point. Further independent testing and examination has verified- in a preliminary fashion
> > at least- both the ejection force and the loosening of QRs.
>
> I agree with the ejection force part of the argument. I have done the experiment with loosening
> the QR and applying the front disc. It most certainly does tend to twist the axle out of the
> dropout, but then riding with a loose QR is likely to be hazardous to your health regardless of
> what type of braking system one has.

As many others have posted, people can ride around (on the road) quite a bit with a loose skewer and
come to no particular grief, until they try to life the front wheel off the ground. On a mountain
bike or over rough surfaces, this is not so true- and of course we are mostly talking about mountain
bikes in these threads about disk brakes.

> The big question revolves around whether or not this ejection force is a cause for concern when
> set against a properly tightened QR, and that is where things get real sketchy. You see, lots of
> parts on a bicycle are bolted together and have forces working against them.

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.

> Cranks are an excellent example and crank bolts work loose all the time for some unfortunate
> people. It is a big problem.

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.

> I have seen countless complaints from people who have to tighten their cranks constantly, but I
> have yet to see someone complain that they must constantly stop to tighten front QRs.

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.

> If this was a common problem, then we wouldn't have needed James Annan to tell us about it. I'm
> sorry I have to be the one to say the Emperor wears no clothes, but there just isn't a body of
> evidence to back up this tempest in a teapot, hence the CPSC judgement.

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.

 

[Tim McNamara]

In article <[email protected]>, Jose Rizal <_@_._> wrote:

> I've read your protestations against the questioners of the whole issue, but your arguments have
> merely been the echoing of what others understand the problem to be. By your own admission your
> background is in the non-engineering, soft sciences, yet you accuse others of failing to "apply
> basic freshman-year engineering pronciples to the design". Without being insulting about it, have
> you personally verified the calculations, applied the theory of the proposed underlying
> principles, and made some quantitative analysis of your own?

No insult taken- it's a fair question. I've looked at the available math which is pretty easy to
follow, even for someone without an engineering background. I couldn't have created the math from
scratch, without a fair amount of preparatory reading, but understanding it is a different matter-
high school algebra and geomtry are sufficient. The proposed underlying principles are simple as is
the linkage between them.

I don't have the equipment to do a quantitative analysis, but I have done the qualitative analysis
to demonstrate the presence of the ejection force with disk brakes and the lack of that force with
caliper brakes, cantilever brakes, V brakes and drum brakes (the latter, by the way, did also appear
to put some displacement force on the axle, possibly oriented normal to a line from the axle to the
attachment point of the brake arm).

The obligation of the manufacturers was to apply basic engineering principles to the design, and
they clearly did not do so (or they ignored the results). It's not the obligation of the consumer to
do such analysis. Of course, as I've already noted, I had to be convinced about the existence of
this problem since I had subscribed to the notion that "all failures of the QR to retain the wheel
are due to operator error, not to QR failure." I had to chew my way through every step of the
reasoning to come to agreement with Annan. I wanted him to be wrong. He's not.

 

[James Annan]

Jose Rizal wrote:

> You're now just being selective. There have been quite reasonable questions about the mechanism
> for loosening QRs which have not been satisfactorily (quantitatively) answered, and in fact at
> least one of the "references" pointed at for this (eg the German mob) has stated that more work is
> required.

I've just given another couple of references where bike shop owners have recreated the skewer
loosening repeatedly and reliably. There have been many more observations of occasional and
intermittent loosening, in situations such that no-one has been able to suggest a plausible
'operator error' to explain the observations. Most people have understandably not gone out of their
way to repeat the experience.

Interestingly, one of those shop owners (Ben Cooper of Kinetics) offered the following response to
the CPSC decision:

"It's good that the CPSC have decided not to investigate - if they did, you could probably have
kissed goodbye to mountain biking in it's current form."

He certainly knows from his own investigations that there is a real problem. In an amusing reversal
of our usual roles, it is my turn to accuse him of scaremongering with his 'goodbye to mountain
biking' comment.

James

 

[Mike S.]

"Tim McNamara" <[email protected]> wrote in message
news:[email protected]...
> In article <AuS3b.32715$cj1.4239@fed1read06>, "Mike S." <mikeshaw2@coxDOTnet> wrote:
>
> > Watching "the disc brake/QR is faulty" crowd bash it out with the "there's no problem crowd" and
> > laughing at everyone. I fall firmly into the "there's no real problem" crowd till proven
> > conclusively that there's a significant occurrence of failures. This is especially true since I
> > actually mtn bike on a bike with discs, unlike some of the "its the design" crowd.
>
> Too bad you lack either the abiliy or the willingness to comprehend the fact that there is a
> serious design flaw, and the fact that the flaw has been verified by independent researchers. It's
> really very simple, and burying your head in the sand doesn't make the problem go away.
>
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.

> 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? The numbers CERTAINLY make it a
national emergency! Try some more, please.

Hell, I'll bet that you don't even ride a mtn bike with disc brakes!
>
> > I just went out and examined my dropouts. You'd think with the prevalence of the problem we're
> > talking about, that there'd be scores where the axle/QR was moving around. Nothing other than
> > the normal imprint from attaching the wheel (in one spot) and there's no scoring on the lawyer
> > lips from the wheel partially ejected. I don't overtighten my QR, so please explain to me why
> > there's a problem again...
>
> No. Why continue to waste my time on you? It's been explained.

I have to disagree. Its been ASSUMED that there's a problem. But like so many things in this world,
I'll agree to disagree if you will. Like I've said before, I'm man enough to admit that if there is
a real problem, AND it can be proven, I'll be one of the first to change my beliefs. I don't see
that there's sufficient amount of proof, so my opinion stands till proven otherwise.

As a follow-on, I went over to the Supergo across the street to do an informal poll of the guys.
Even the mechanics (one of whom likes to hurl himself and his bike over big jumps) have never heard
of, or had seen anyone with their wheel being ejected out of their bike.

So, I say again: what's so stinkin bad about the design if there aren't any people having real
problems that can't be traced to problems with the QR?

Mike

 

[Jobst Brandt]

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.

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

 

[Spider]

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.*

> 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. 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. There are all sorts of compromises on a
bicycle - and each has to be weighed against the benefits. And to the cost of the solution.

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

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.

> > If you can't answer the questions, say "I don't know." If you know the answer, post it or the
> > link. If you find the questions tiresome, don't bother responding. You (and the others) do
> > yourself a DISservice by being defensive and obtuse.
>
> There's nothing obtuse about the hypothesis.

I'm not talking about the hypothesis, and we both know it. I'm talking about follow-up questions.
Follow-ups that are routinely dismissed in a condescending fashion, with the phrase "a freshman
physics student could understand it." Really? Then where is that frosh to tell me what the mu of
knobbies on dirt happens to be? It's a critical number.

> It's simple, straightforward and based on sound engineering principles.

Each of the component parts is relatively simple, I will agree. There *is* an ejection force. There
always has been, BTW. It's been called, up to this point, "gravity." But nevermind that - the
interaction between ALL the parts is what is complex, and the things tying all these things together
are either dismissed as insignificant without explanation, or just flat not responded to.

> 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?

How about those of us who are trying to understand how the whole thing works together? Those of us
who know that freshman physics is, at best, a gross approximation of what happens in the real world?

Spider