Disc brake front wheel ejection: fact or fantasy?

(Spider) wrote in message . com...
(James Annan) wrote in message . com...

http://www.boltscience.com/pages/vibloose.htm

What has this to do with cammed, knurled-surface QRs, again?

Hey, it didn't mention the colour or any other irrelevant detail. Why
not mention the purple anodising too?

and not brought bang up-to-date a few weeks ago with this irrelevant
demonstration that has absolutely nothing whatsoever to do with
unscrewing of QR skewers:

http://kinetics.org.uk/html/disc_brakes___qrs.html

If you think that this website actually supports your hypothesis, you
haven't read it. His one (1) experiment with a Ti skewer is not
representative.

His conclusions are about the same as the most of the MTB community
that has read your hypothesis.

His conclusion is that the CPSC had better not look into it carefully,
because he has seen that there is a real problem.

In
any case, your motivations are certainly not as clear as you pretend
they are.

I'd be grateful if you could help me out and tell me what they are.
Oh, and while you're doing the mindreading, how about telling me what
I'm having for breakfast next Tuesday.

James

James Annan said...

Unproven since the 1960s, as lamely described on this far-fetched web
site:

http://www.boltscience.com/pages/vibloose.htm

But they aren't talking about bicycle skewers, are they? Bicycle skewers
have safeguards against just this sort of thing happening. The heavily
knurled surfaces in contact with the soft metal of the forks are going
to be a major obstacle. I also noticed that my bolt-on skewers have a
buffer against your purported unscrewing mechanism. The allen head spins
freely inside the cup that has the knurled surface that clamps to the
dropouts. This will isolate it from any torque that might act to unscrew
it if the friction in the threads is greater than the friction of the
allen head against the cup, especially if the allen head is on the same
side as the brake. I don't know which side has more friction, but my
guess is that the threads have more, and consequently this setup isn't
very likely to unscrew, even if we suspend disbelief and accept your
theory as fact. This effect can be enhanced by putting graphite in the
cup and allen head interface and using thread lock on the threaded side.

and not brought bang up-to-date a few weeks ago with this irrelevant
demonstration that has absolutely nothing whatsoever to do with
unscrewing of QR skewers:

http://kinetics.org.uk/html/disc_brakes___qrs.html

With all due respect to the author of the article, I'm sure he's a nice
guy and means well, but this ranks among the most superficial and
unscientific 'experiments' I have ever heard of. I'm surprised you
bothered to point it out. He wants to see if there is unscrewing
happening, but he didn't even do something as basic as putting matching
hash marks on the fork and skewer or checking the dropouts for telltale
signs of wear. If a properly tightened skewer is forced to move in the
dropouts, IT WILL DAMAGE THE DROPOUTS. I really don't know how to make
it any plainer. If this were happening as often as you claim, then we
would all see it and it would have been thoroughly discussed before now.
Aside from that, he didn't come down very hard on your side. He said
that his QR and disc brake combo hadn't loosened in a year and a half of
riding when tightened to his own satisfaction. He also said the effect
disappeared when the cam lever was installed on the left. I can't think
of a reason why this would nullify the alleged unscrewing effect,
because a QR isn't isolated from the clamp surface the way the allen
head in my bolt-on skewer is. But I suppose there would be some
isolation since they aren't welded together.

I don't expect that he, or anyone else for that matter, agrees with
every word I have said - in fact, I'm not sure that even I agree with
every word that I've said - but what I've heard from him and his
friends has been generally supportive. If you or anyone else wants to
see what he said not long ago try reading this:

http://www.singletrackworld.co.uk/fo...8#reply_523608

James

Russ's accident was a tragic thing to be sure. That it could have been
any one of us makes it hit even closer to home. As such, it would have
been hard to chime in on that discussion with a dissenting point of
view. You seem to focus much of your attention on downhill accidents,
like what happened to Russ. Downhill is certainly the most dangerous
part of a ride and the brakes play a key role there, but a small problem
with that hang up is that a downhill is the last place we would see the
maximum brake ejection force. Brakes must be used judiciously and gently
going downhill, or you will just skid out the front wheel or endo. Going
downhill, the friction available to the wheels will be smaller, and
since you are already at an angle, less force will be required to
produce an endo. You will see the maximum ejection force on level
ground. So your proposed loosening isn't likely to start on the downhill
if the skewer stayed tight through the rest of the ride. The only thing
you can say is that if the skewer is already loose, the downhill can
quickly provide the agitation to finish it off.

I'm not going to say I know what happened in this accident. It sounds to
me like it all happened so fast that nobody knows how it unfolded. This
is typical of most of my own comparatively minor trail accidents, as I
have said previously. I'm being perfectly honest when I say that until
there is more evidence in your favor, I don't see how you are doing
anyone any favors by linking this accident to your theories. In spite of
your condescending arrogance, you have failed to impress the CPSC, or
anyone else with the power to affect change, that there is any hard
evidence in support of your claims. But carry on like you have. I'm sure
the whole thing will die of apathy and be forgotten soon enough.

(James Annan) wrote in message . com...
(Spider) wrote in message . com...
(James Annan) wrote in message . com...

http://www.boltscience.com/pages/vibloose.htm

What has this to do with cammed, knurled-surface QRs, again?

Hey, it didn't mention the colour or any other irrelevant detail. Why
not mention the purple anodising too?

Hmmm, here's a couple of "irrelevant details" from the website you
gave:

"Through the efforts of the American National Standards Subcommittee
B18:20 on locking fasteners, three basic locking fastener categories
have been established. They a free spinning, friction locking, and
chemical locking.

The free spinning type are plain bolts with a circumferential row of
teeth under the washer head. These are ramped, allowing the bolt to
rotate in the clamping direction, but lock into the bearing surface
when rotated in the loosening direction. The "Whizlock" is in this
category."

And,

"In general terms, the key to preventing self loosening of fasteners
is to ensure that :

1. There is sufficient clamp force present on the joint interface to
prevent relative motion between the bolt head or nut and the joint.

...."

Now, let's see here - knurling, and a cam-activated mechanical
advantage lever to get more clamping. How odd that you would consider
these two important parts of the QR irrelevant.

You are nearly Vandemanesque in your ability to see the data you like,
and "not see" the data that inconvenient. Perilously close to what is
know as "junk science."

and not brought bang up-to-date a few weeks ago with this irrelevant
demonstration that has absolutely nothing whatsoever to do with
unscrewing of QR skewers:

http://kinetics.org.uk/html/disc_brakes___qrs.html

If you think that this website actually supports your hypothesis, you
haven't read it. His one (1) experiment with a Ti skewer is not
representative.

His conclusions are about the same as the most of the MTB community
that has read your hypothesis.

His conclusion is that the CPSC had better not look into it carefully,
because he has seen that there is a real problem.

Here is the only thing he actually said about the CPSC:

"The CPSC in the States is investigating, but they have not been the
most balanced cycling test body on previous occasions."

He also says this:

"Unlike James Annan, I do not believe that there is a fatal design
flaw with *all* combinations of disc brake, fork and quick release."

In his conclusions, he says this:

"There are three levels of solution, depending on how paranoid you are
feeling at the moment...

Level 1 paranoia: (cheap or no-cost DIY solutions)

*
Use a good quality branded skewer from one of the major
manufacturers - make sure that it has good serrations and that the
lever action feels smooth and has a definite "clunk" as you close it.
*
Fit the skewer with the lever on the left side. This means that
the entire skewer has to turn, instead of just the nut, making visual
checks easier.
*
Close the lever as hard as you can manage by hand - it should
leave a definite imprint in your palm (if you use your palm). If you
don't have that much hand strength, lay the bike on it's side and
stand on the lever, but don't go OTT.
*
Make sure that the lever is not touching anything when it's
closed - it should not be touching the fork leg, for example. I know
it's not as neat, but closing the skewer so it points horizontally
backwards is the best way.
*
Use a releasable cable tie to sttach the lever to the fork leg,
to stop it flipping open.

Level 2 paranoia: (cheap low-hassle aftermarket solutions)

*
Several manufacturers are producing (or have on the drawing
board) various types of locking skewer. These could be a good idea,
assuming that they lock with enough force, as they'd prevent any
vibration loosening.
*
Use a solid axle nutted hub instead. The clamping force of a
10mm nut is much higher than that of a QR skewer, which is why track
bikes use them.

Level 3 paranoia: (serious bombproof solutions)

*
Use a bolt-through front hub. This requires new forks and a new
wheel, but is totally solid.
*
Several manufacturers are introducing forks with forward-facing
dropouts - this means that the ejection force is no longer pushing the
axle out of the slot.
*
Use forks with the caliper on the front of the right fork leg.
This alters the angle of the force so it is no longer a problem. This
would require a custom fork, of course.

Personally, I'm a level 1 person..."

No, James, he just doesn't agree that this is an earth-shattering
problem. THe fact that you would misrepresent his analysis speaks to
your obfuscation on the issues.

In
any case, your motivations are certainly not as clear as you pretend
they are.

I'd be grateful if you could help me out and tell me what they are.

Well, that a clever bit of irony, but considering the other two claims
that you have made in this last post of yours, shown to be hilariously
misleading at best, your claims of purity of motivation strike me as
hollow, tending toward disingenuous. I won't call you a deliberate
liar, because I do not know if this is the case of not. But your
communication style has again gotten in the way of your message, and
you are doing your best to alienate the folks you should be trying to
recruit.

My apologies for quoting so much material - I just wanted to be clear
that what James says, and what is actually written, can be two
entirely different things.

Spider

Super Slinky wrote in message et...

But they aren't talking about bicycle skewers, are they? Bicycle skewers
have safeguards against just this sort of thing happening. The heavily
knurled surfaces in contact with the soft metal of the forks are going
to be a major obstacle.

They are talking about threaded bolts in general, which includes
skewers. They specifically mention the value of knurling, but it's
clear that the mechanism by which this works (when it does) is by
preventing movement. When it fails to prevent movement, it won't
prevent unscrewing either.

I also noticed that my bolt-on skewers have a
buffer against your purported unscrewing mechanism.

I'm not talking about your skewers. Perhaps this is why you've been so
hostile - did you think I was telling you that _your_ skewers were
slipping and unscrewing, and you had failed to notice? Of course I
believe you when you say this has not happened. All I have been trying
to say is that _some_ skewers have been seen to slip and unscrew, even
when correctly used.

http://kinetics.org.uk/html/disc_brakes___qrs.html

With all due respect to the author of the article, I'm sure he's a nice
guy and means well, but this ranks among the most superficial and
unscientific 'experiments' I have ever heard of.

I agree, but he happens to be the only person (that I know of) who has
bothered to (a) measure the unscrewing repeatedly, and (b) put up a
web page about it. So it's a handy reference. Unless you think he's
lying, or too incompetent to make this simple observations, it's hard
to avoid the conclusion that his skewer did, in fact, unscrew.

If a properly tightened skewer is forced to move in the
dropouts, IT WILL DAMAGE THE DROPOUTS.

Probably there will be some fretting, yes. I'm not sure what point you
are trying to make here. Unless you think that the velotech lab faked
their measurements (and even photos too) then their skewer certainly
moved. In fact Ernst Brust says he has known about this skewer
movement for several years and has warned manufacturers, but they have
ignored him. Although IMO this alone is prima facie evidence of a bad
design (the axle isn't supposed to move under ordinary braking forces)
it seems like no-one had previously thought of the potential for
unscrewing from repeated transverse movement, so the danger wasn't
apparent.

I really don't know how to make
it any plainer. If this were happening as often as you claim, then we
would all see it and it would have been thoroughly discussed before now.

I haven't made any strong claim as to the frequency. It happens to
some people, and to a subset of them, it's a very real problem.

Downhill is certainly the most dangerous
part of a ride and the brakes play a key role there, but a small problem
with that hang up is that a downhill is the last place we would see the
maximum brake ejection force. Brakes must be used judiciously and gently
going downhill, or you will just skid out the front wheel or endo. Going
downhill, the friction available to the wheels will be smaller, and
since you are already at an angle, less force will be required to
produce an endo. You will see the maximum ejection force on level
ground. So your proposed loosening isn't likely to start on the downhill
if the skewer stayed tight through the rest of the ride. The only thing
you can say is that if the skewer is already loose, the downhill can
quickly provide the agitation to finish it off.

Certainly hard braking on level ground can provide exceptionally large
momentary forces - this is why Planet-X recently changed the angle of
their dropouts, since rider(s) (cerainly Brant Richards, another vocal
critic of me, has reported it, and they give this explanation on their
website) can move the front wheel when doing low-speed stoppies.

Some people have reported loosening under rather tame testing (like
Ben Cooper) but it seems reasonable to me that fast rough downhill is
particularly testing as it will can generate lots of up and down
forcing in a very short interval of time. There needs to be
significant upwards forcing too, as the steady force of body weight
alone will probably not be enough to move the axle back up to the
correct position. Hitting bumps fast can certainly provide that. I
don't see any reason why friction itself is reduced by a slope, and it
takes a very steep slope to prevent firm front brake use if the
terrain is reasonably firm.

I'm sure
the whole thing will die of apathy and be forgotten soon enough.

Planet X and a couple of tandem builders have already made design
changes, rumour has it that Pace may do for next year and (according
to the journalists involved) the major manufacturers have all but
promised it for 2005 in the hope that the journalists will shut up
about it. That doesn't sound like apathy to me. In fact it seems to me
that things are pretty well wrapped up except for how to deal with the
forks in use and being sold at the moment. That's where the debate
should be, not on whether the problem exists at all.

James

James Annan said...

I'm not talking about your skewers. Perhaps this is why you've been so
hostile - did you think I was telling you that _your_ skewers were
slipping and unscrewing, and you had failed to notice? Of course I
believe you when you say this has not happened. All I have been trying
to say is that _some_ skewers have been seen to slip and unscrew, even
when correctly used.

I guess that is part of the problem and where a lot of the disagreement
is. If this is true, maybe more energy should have been spent trying to
see what their specific problem is and how it can be remedied using what
we have available to us now. After looking at my bolt-on skewers, I
think that most of your concerns, whatever merit they may have, can be
addressed with skewer design. If the QR cam lever and nut were isolated
from the clamping surfaces, and the nut was a locking design that had
more friction with the threads, your proposed unscrewing mechanism would
have another major obstacle to overcome. When combined with retention
lips, a skewer like this would have the even better safety benefit of
making it far less likely to loose the wheel if the rider forgot to
tighten it or tightened it inadequately. It wouldn't as easily unscrew
the rest of the way from vibration, no matter what brake system was
used. But a simple fix like this begs the question why it hasn't already
been done. The obvious answer is that very few people have a problem
with skewers the way they are now. It would be more expensive skewer
with more parts to lose and it would be harder to get on and off. Would
anyone want it or pay extra for it?

Another shameful consequence of you trying to railroad through wholesale
changes to a design that appears to be safe and functional for almost
everyone might be that new designs may turn out to be ultimately less
safe than what we have now. Since countless thousands of people have
been using the current design with so few problems, how long is it going
to take us to really know if there has been a net gain in safety? If new
designs cause twice as many accidents as we have now, who will ever know
if there isn't another media induced hoopla to point it out? We would
never know about the unintended consequences of increasing costs or
diverting scant engineering and tooling resources toward this instead of
something else that might be even more beneficial.

I agree, but he happens to be the only person (that I know of) who has
bothered to (a) measure the unscrewing repeatedly, and (b) put up a
web page about it. So it's a handy reference. Unless you think he's
lying, or too incompetent to make this simple observations, it's hard
to avoid the conclusion that his skewer did, in fact, unscrew.

That is your take on it. Mine is different. I don't think there is
enough information there to make it noteworthy.

Probably there will be some fretting, yes. I'm not sure what point you
are trying to make here. Unless you think that the velotech lab faked
their measurements (and even photos too) then their skewer certainly
moved. In fact Ernst Brust says he has known about this skewer
movement for several years and has warned manufacturers, but they have
ignored him. Although IMO this alone is prima facie evidence of a bad
design (the axle isn't supposed to move under ordinary braking forces)
it seems like no-one had previously thought of the potential for
unscrewing from repeated transverse movement, so the danger wasn't
apparent.

The point I'm trying to make is that this is the smoking gun if there is
one. It is physical evidence, not anecdotes, not amateurish experiments
or force equations. If properly tightened skewers are being jerked
around as you say, then damage to the dropouts will be seen. There would
be a clear difference between the condition of the brake side dropout
and the right side dropout. The paint would be stripped away and there
would be an oval shaped wear pattern with considerable scoring of the
metal on the fork leg and metal shavings. If you had been producing this
kind of evidence from the start, then you would have something.

You keep repeating the Velotech testing as if it is irrefutable proof of
what you say, but I'm not so easily impressed by one lab in a foreign
country doing tests using equipment and conditions that I know nothing
about. Nor do I accept your implication that what they have done is
somehow infallible or above reproach. I don't know what their reputation
is, how they are funded, if they are audited or regulated or anything
else that might shed some light on what they are trying to prove. I work
in a testing lab and I know how difficult it can sometimes be to produce
data that is free from error or flawed test methods. What I have heard
about the Velotech testing hasn't made me want to go buy a thru-axle
fork just yet. The last I heard the testing was incomplete and merely
showed that the axle moved under brake load. You proved more than that
with your accident and the resulting photos. It didn't say they had been
able to get a skewer to unscrew, which you claim is the basic threat, or
that they had even been able to show that there is up and down movement.

Certainly hard braking on level ground can provide exceptionally large
momentary forces - this is why Planet-X recently changed the angle of
their dropouts, since rider(s) (cerainly Brant Richards, another vocal
critic of me, has reported it, and they give this explanation on their
website) can move the front wheel when doing low-speed stoppies.

I looked at the Planet-x forks and I saw that they shared most of the
unfortunate design qualities of your tandem fork--lack of retention
lips, rearward facing dropouts, steel construction. Not that there is
anything wrong with steel, but the vast majority of disc brakes are
mounted to magnesium suspension forks which would provide a better grip
for the skewer.

Some people have reported loosening under rather tame testing (like
Ben Cooper) but it seems reasonable to me that fast rough downhill is
particularly testing as it will can generate lots of up and down
forcing in a very short interval of time. There needs to be
significant upwards forcing too, as the steady force of body weight
alone will probably not be enough to move the axle back up to the
correct position. Hitting bumps fast can certainly provide that. I
don't see any reason why friction itself is reduced by a slope, and it
takes a very steep slope to prevent firm front brake use if the
terrain is reasonably firm.

The frictional force available from the ground on the slope is reduced
by multiplying the weight of the bike and rider by the cosine of the
angle of the slope. On level ground, you get all of the frictional
force. Falling off a cliff, the friction of the cliff face is irrelevant
because you have no weight pressing against it. Level ground: Cos(0º)=1,
falling off a cliff: cos(90º)=0. On a 25º slope, 10% of the maximum
braking force is lost. The slope also raises the center of gravity
relative to the axle, decreasing the force required to produce an endo,
and consequently reducing maximum braking force yet again by the same
factor. All if this is in addition to the fact that the typical
coefficient of friction of a dirt trail will always be much less than on
pavement. To sum it all up, the largest maximum braking force will be
seen on level pavement and the smallest maximum braking force would be
on a downhill slope off-road. My point is that your proposed unscrewing
mechanism isn't likely to start on a downhill.

The force required to move the axle back up if it is forced down from
its original position by braking force is also a very important
question, as Joe Riel pointed out in r.b.t. We know that the downward
force must be considerably greater than the upward force, or your brake
induced movement of the axle can't happen. In addition to that, the
upward force will increase to its maximum at the same time that the
downward force is approaching its critical point, because all of the
weight of the bike and rider will shift to the front wheel.

But it gets worse. 95-99% of disc brakes are mounted to suspension
forks. This means that the almost all the weight on a front axle is
sprung weight and this greatly decreases the upward forces generated.
That is what a suspension does, and that is why the upward force needed
to produce that up and down unscrewing motion of yours may not be
possible, because the upward force must also overcome the clamping force
of the skewer and there is a very limited amount of upward force
available.

Planet X and a couple of tandem builders have already made design
changes, rumour has it that Pace may do for next year and (according
to the journalists involved) the major manufacturers have all but
promised it for 2005 in the hope that the journalists will shut up
about it. That doesn't sound like apathy to me. In fact it seems to me
that things are pretty well wrapped up except for how to deal with the
forks in use and being sold at the moment. That's where the debate
should be, not on whether the problem exists at all.

Whatever. If this is true, then I guess we can thank you for increasing
our costs and possibly delaying other innovations that might have proved
more useful.

(James Annan) wrote:

Planet X and a couple of tandem builders have already made design
changes, rumour has it that Pace may do for next year and (according
to the journalists involved) the major manufacturers have all but
promised it for 2005 in the hope that the journalists will shut up
about it. That doesn't sound like apathy to me. In fact it seems to me
that things are pretty well wrapped up except for how to deal with the
forks in use and being sold at the moment. That's where the debate
should be, not on whether the problem exists at all.

All contributors to these Annan Principal threads are starting to
sound like broken records.

I'll repeat my main point one more time:

The "problem" - assuming it IS a problem - is a relatively
insignificant one as far as the bicycle industry is concerned: it's
frequency of occurrence is negligible when viewed against the total
number disc brake equipped mountain bikes with QR's in use. No huge
lawsuits have been filed; no horrible publicity has been generated a
la Ford Pinto and Firestone tires. Moreover, the CPSC, having been
alerted to the issue by Annan, has determined there is insufficient
evidence to date in order to determine the brake/fork/QR configuration
constitutes a "substantial product hazard" under Section 15 of the
CPSA.

Consequently, the industry has no incentive whatsoever voluntarily to
recall or modify existing equipment is use. It would be prohibitively
expensive and would "kill" the industry. Future equipment may well
incorporate designs to eliminate any hint or questions of wheels being
ejected due to disc brake forces. But until such time as it becomes
more cost effective to recall the existing product than to maintain
the status quo (huge lawsuits) or the CPSC requires it, there will be
NO change in the status quo and NOTHING will be done about forks in
use and sold at the moment.

You can take that to the bank,

--dt

Chris Phillipo wrote:

Now if Joe Machineshop comes up with this magical design that clamps
with 5 times the force and fits in a standard droupout/hollow axle, Joe
might make a ton of money capitalizing on this problem that doesn't
exist, thanks to his unwitting lackys. Joe would do well not to let
this greed get the best of him and skip out to the Bahamas before
collective damage his design has caused to frames everywhere becomes
evident.

His name is "James," not Joe.

--dt