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Cannondale's tests of disks and QRs



 
 
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  #21  
Old September 16th 04, 01:48 PM
SuperSlinky
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Helen Deborah Vecht said...

James Annan typed

"A light hand force of 5 lbs was


Umm... I used to have a grip of 100lb[1]. Of what would 5lb be representative?

[1] measured by hand surgeon doing research.

--
girlie


A bike rider using the brake but not wanting to lock the wheel or go
OTB? What do you think would happen if you used that 100lb grip on the
brakes going 15.5 mph? Oy, this topic is getting very tired, and all the
dweebs trying to concoct a grand conspiracy theory about it is just
pathetic. In fact, I would suspect that the typical grip on the brake
lever at 15.5 mph would be much less than 5 lb.
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  #22  
Old September 16th 04, 02:14 PM
SuperSlinky
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Bonehenge said...

I'm on the Board of Directors for a mountain bike advocacy group with
almost 700 members in our chapter, and thousands more across other
states. I also work at a very busy bike shop. We are located in the
US within driving distance for Plattekill Mountain, Mount Snow, and
other competitive downhill locations. I have no connection to any
manufacturer, bike, fork, or anything else.

News of wheel ejections on disc brake equipped bikes would travel very
fast, along the lines of "Did you hear what happened to my buddy?"
The tale would grow taller as it passed down the line, and eventually
everyone would have a "buddy" who had this happen. This is news that
would travel quickly at events and festivals.

No one that I know has EVER heard of this, 'nor do we see forks with
damaged QR seating areas coming in for service at the shop.

Should I wear a "sandwich board" to Interbike looking for someone who
is familiar with this widespread problem? Forgetting to close the QR
dosen't count! G

Barry


The only place you will hear about it is on Usenet and a few UK based
message boards. I believe there is one clear case of it happening--to
James Anaan. But instead of him coming to the common sense conclusion
that his case was a perfect storm of bad ingredients, he runs around
like Chicken Little telling everyone the sky is falling. He had a steel
tandem fork without retention lips and a very unfortunate dropout angle.
The tandem allows extraordinary leverage and braking forces. You won't
be doing an endo by locking the front brake on a tandem. The dropouts
were angled perfectly to allow the wheel to pop out if the disc brake
pad was a pivot. No retention lips. The painted dropouts meant that the
only thing that was really holding the wheel to the fork was the
friction of the paint on steel.

In the very beginning, he had an interesting story to tell. Now he is
like Don Quixote, trying to create a reality that never existed.
  #23  
Old September 16th 04, 02:44 PM
Peter Clinch
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SuperSlinky wrote:
Bonehenge said...


News of wheel ejections on disc brake equipped bikes would travel very
fast, along the lines of "Did you hear what happened to my buddy?"


If your buddy was Russ Pinder then it might have done just that...

The only place you will hear about it is on Usenet and a few UK based
message boards. I believe there is one clear case of it happening--to
James Anaan. But instead of him coming to the common sense conclusion
that his case was a perfect storm of bad ingredients, he runs around
like Chicken Little telling everyone the sky is falling.


It probably was a perfect storm of bad ingredients, but perfect storms
of bad ingredients can happen, and if they can still be avoided without
too much extra trouble then there's no good reason not to avoid them.
Unless you think complacency is a good reason.

Or you could just bluster about saying it hardly ever happens, so it's
not a problem. Like Chernobyl, for example...

Pete.
--
Peter Clinch Medical Physics IT Officer
Tel 44 1382 660111 ext. 33637 Univ. of Dundee, Ninewells Hospital
Fax 44 1382 640177 Dundee DD1 9SY Scotland UK
net http://www.dundee.ac.uk/~pjclinch/

  #24  
Old September 16th 04, 02:55 PM
jim beam
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James Annan wrote:
jim beam wrote in message ...


polite as always. james, the point is not my "single case" but the lack
of cases that you present to the contrary. post some pics of forks
evidencing slippage if you please.



http://www.velotech.de/saz_12_-_03_-_05.pdf

which I found by googling a previous post of mine in r.b.t, so don't
pretend you haven't seen it before. Unfortunately, I can't find the
rebuttal that you presumably offered, so I'd be grateful for a
reminder.


i have deep regret that

1. my german is not strong enough to follow all of the text
2. that i don't have either the time or the ax to grind to look for this
stuff.

only when i show up on r.b.t. do i ever get to see articles like that,
so please james, emotive language like "don't pretend you've never seen
it before" merely serves as antagonism.



now, to address your cannondale point, it is clearly a carefully guarded
response, but i fail to see how you'd expect anything else



Is this really all you can bring yourself to say about it?

Let me remind you of their test:


"A light hand force of 5 lbs was applied to the brake lever every 10
seconds for 3 seconds duration. This caused braking torque to be applied
to the wheel. The drums had 3 equally-spaced cleats (0.5" high the same
as those used on wheel fatigue test T027) to create bumps for the front
wheel to go over."

And then we have:

"Conclusion:

"The conclusion is that the braking action of disc brakes is not causing
the quick release mechanism to unscrew. This test is unable to cause
loosening. At this time there are no reasons to believe that anything is
missing or over constrained in this test."


i did read it, thanks. what is restatement trying to achieve?



You describe that as "carefully guarded, but i fail to see how you'd
expect anything else"!

Remember that this is not just something they happened to have done
and offered to throw into the ring, but a piece of work they were
specifically commissioned to do by the CPSC in order to investigate
whether there was a potential danger.

Have you really no "reasons to believe that anything is missing or
over constrained in this test"? You have no opinion beyond "carefully
guarded, but i fail to see how you'd expect anything else"?

I would be equally amused to hear Mark Hickey's assessment of this
test, and Tony Raven's, too.


you're just too busy being a victim to make progress in this. if you're
serious about getting traction, why don't /you/ commission an
independent test from a reputable third party and have your attorney
submit it? habeus corpus. any attorneys here want to represent james?

  #25  
Old September 16th 04, 03:17 PM
Tony Raven
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James Annan wrote:


I would be equally amused to hear Mark Hickey's assessment of this
test, and Tony Raven's, too.


I'm staying out of this. My views are well known and there is not a lot
of point repeating them in the church of the faith. I did plan to do
what no-one seems to have done and go and find out what 5lbs force on
the brake lever was like. I know I don't squeeze my brakes as hard as I
possibly can so I know 100lbs is not realistic. However I have no idea
at present what 5lbs represents in my normal range of braking. Is it
top end, bottom end, middling? Can anyone here say yet because until
they can then ridiculing the figure absent realistic reference points is
conviction not scientific enquiry.

Damn, I just got sucked in.

Tony

  #26  
Old September 16th 04, 03:36 PM
Gary Young
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jim beam wrote in message ...
James Annan wrote:
jim beam wrote:

James Annan wrote:
snip

"The conclusion is that the braking action of disc brakes is not causing
the quick release mechanism to unscrew. This test is unable to cause
loosening. At this time there are no reasons to believe that anything
is missing or over constrained in this test."


james, did you check out the pics i posted of my own disk brakes?



Yes, but if you thought I'd be interested in a single case of "my wheel
didn't slip" then you have missed the point very very badly indeed.


polite as always. james, the point is not my "single case" but the lack
of cases that you present to the contrary. post some pics of forks
evidencing slippage if you please. dismissal of evidence that
contradicts your accusations does not add credibility to your case.

bottom line is this; put yourself in the position of a manufacturer.
are you going to pay attention to a guy on the net who, with respect,
misses a vital part of their analysis, then descends to personal attack
when challenged, or are you going to rely on your distributor network's
return data?


This from Mr. Sock Puppet! It's too rich! Did it ever occur to you
that few people pay attention to your counterexample not only because
it's somewhat beside the point, but that you've proven yourself
unreliable here on rbt? James may be "a guy on the net," but at least
he makes his name and his qualifications known. By your own reasoning,
we should give no credence to you.


trust me, i have been carefully on the lookout for potential ejection
problems among all the people i've ridden mountain with since you raised
this issue, and you may be interested to learn that i have actually seen
one case of slip! but problem is, there was no ejection and it was
clearly attributable to an open cam skewer, badly crudded up, that the
rider couldn't be bothered to close properly. so, like a broken chain
that's attributable to it not being fitted correctly or an under-clamped
brake cable slipping and causing brake failure, the only disk wheel
slippage i've seen was due to incorrect skewer deployment. and even
then, if i hadn't been specifically looking for the slippage, the rider
would never have known because he hadn't, nor had he /ever/ had, any
problems! certainly not anything as serious as ejection.

now, to address your cannondale point, it is clearly a carefully guarded
response, but i fail to see how you'd expect anything else in the face
of a serious liability threat that's not supported by any statistical
evidence.


It wasn't a carefully guided response. It was a confidential
communication between Cannondale and the CPSC and under the
circumstances both of them probably have a legal duty to be forthright
about the facts regardless of the legal consequences.

Furthermore, to the extent statistics has a bearing on this issue, it
also should clue you in to why your counterexample doesn't count for
much. Does the fact that I could take photographs of thousands of
upright SUVs mean that SUVs don't have a rollover problem?

mtb brakes changed from cantilever to linear p.d.q. once it
was established that incorrect usage combined with fouling could send a
rider over the bar. i don't know the numbers, but i'll wager there were
not many o.t.b's before manufacturers made the switch, however
statistically unlikely. unless disk brake ejection is actually
evidenced, then who is going to fix a problem that doesn't exist?


Now, have you any "reasons to believe that anything is missing or over
constrained in this test"?

Inquiring minds want to know...

James

  #27  
Old September 16th 04, 05:20 PM
Werehatrack
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On Wed, 15 Sep 2004 15:05:32 +0100, Helen Deborah Vecht
wrote:

James Annan typed

"A light hand force of 5 lbs was


Umm... I used to have a grip of 100lb[1]. Of what would 5lb be representative?

[1] measured by hand surgeon doing research.


The grip force required to lock up the wheel is far less than that
with any useful braking system, of course.

Still, it appears to me that they designed a passable test rather than
an exhaustive one. If so, they may have shot themselves in the foot;
should a later determination show that their test was flawed *and that
they had reason to know this*, the investigators will not be pleased.

I agree with another poster's statement; a variety of application
pressures, a range of bump sizes with simulation of jumping (some of
which is "landed" with the brakes engaged), and a higher stress and
load level in general seems to be merited.

In their partial defense, I will note that they seemed to be focusing
solely on the issue of whether common, normal vibration levels in
low-stress riding could result in QR loosening. I'm pretty sure
that's the wrong question, and in any event, they tested only one QR
design. Combined with the lack of test conditions that simulate the
popularly-expected potential failure mode scenarios, I feel that it is
best to regard this test as not dispositive of disc brake safety in
and of itself.

All that said, I'm still going to keep riding the bike that has a
front disc. I'm not convinced that there's a significant wheel
ejection hazard in the type of riding that I do.
--
Typoes are a feature, not a bug.
Some gardening required to reply via email.
Words processed in a facility that contains nuts.
  #28  
Old September 16th 04, 05:28 PM
Dave
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Helen Deborah Vecht wrote in message ...
"Paul - xxx" typed


How was the 5 lbs measured ?


As an ex Torque Control Engineer (Desoutter / Georges Renault) I feel the
tests would be more relevant using a range of braking forces from light to
as much as possible, commensurate with the force a human hand can exert ...


This is, I believe' in the 100-200lb range and consistent with panic braking.

IMHO all bike equipment has to cope well with maxima.


Seems the real world question is how much lever force is required to
lock up the rotor. Beyond that all you are testing is the lever
strength. Given that disc systems are designed for single digit
applications, and most levers accept no more than two fingers, using
full hand grip strength is not valid. I found some data on grip &
pinch strengths at http://www.bleng.com/pdf/grip1.pdf for anyone
interested. Dave D.
  #29  
Old September 16th 04, 06:35 PM
Simon Brooke
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in message , Helen Deborah
Vecht ') wrote:

"Paul - xxx" typed

How was the 5 lbs measured ?


As an ex Torque Control Engineer (Desoutter / Georges Renault) I feel
the tests would be more relevant using a range of braking forces from
light to as much as possible, commensurate with the force a human
hand can exert ...


This is, I believe' in the 100-200lb range and consistent with panic
braking.

IMHO all bike equipment has to cope well with maxima.


The people who point out that if you slam on the brakes on a mountain
bike you go over the top anyway are right, you know; I've seen it
happen. And hydraulic disk brakes are very sensitive. So Cannondale's
five pounds may in fact be typical of the maximum safe braking force;
certainly my Hayes HFX-9 equipped Cannondale has very light brakes. My
own guess would be that panic stop force is slightly higher but it
certainly isn't very high.

Of course by exerting more force you can lock the front wheel. But the
injury consequent on locking the front wheel at speed is not greatly
different from the injury consequent on the wheel ejecting at speed.

This isn't to say that I believe disk ejection can't happen. I think
there's enough independent testimony to indicate it can. But I believe
that it is extremely rare in practice. Me? I ride a Lefty.

--
(Simon Brooke) http://www.jasmine.org.uk/~simon/

;; All in all you're just another hick in the mall
-- Drink C'lloid

  #30  
Old September 16th 04, 07:05 PM
Simon Brooke
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in message , Just zis Guy, you know?
') wrote:

Helen Deborah Vecht wrote:

Umm... I used to have a grip of 100lb[1]. Of what would 5lb be
representative?


A rider on a disk-brake equipped Cannondale being very, very careful
not to make the QR come undone ;-)


There's two major objections to that account. Firstly, most disk brake
equipped Cannondales do not have quick releases on the front. F
series[1] and Chase hardtails, Scalpel, Jeckyll[1] and Prophet full
suspension bikes all have Lefty 'forks' which don't have a removable
front axle. Gemini[2] models have through axles front and rear. The
only models I could find in Cannondale's 2005 'mountain' line up with
both disk brakes and a front quick-release are the F600 and the
remaining Jekyll.

Secondly, as I've pointed out elsewhere on the thread the hand pressure
required to lock the wheel with hydraulic disks is not very high and
while I wouldn't like to say categorically that five pounds is the
maximum safe braking pressure it's in the right ball park.

[1] Some older models have Fatty forks which do have quick release; some
low end models have non-Cannondale forks which do have quick release.
Few of these also have disk brakes.

[2] 2005 models certainly; it's possible that some older models have
quick release.

--
(Simon Brooke) http://www.jasmine.org.uk/~simon/

;; Usenet: like distance learning without the learning.
 




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