Cannondale's tests of disks and QRs

On Tue, 28 Sep 2004 12:41:50 -0700, Slacker
wrote in message opse1yb0q7m83lxu@slacker:

Man, you guys can blow more wind than a Floridian hurricane!
When are you gonna blow out of town (or at least stop x-posting)?!?!?!

At a a guess, when the manufacturers stop selling a product with an
apparent serious fault, or produce some credible figures to prove that
the apparent serious fault is not, in fact, an issue. Why?

Guy
--
May contain traces of irony. Contents liable to settle after posting.
http://www.chapmancentral.co.uk

88% of helmet statistics are made up, 65% of them at Washington University

On Tue, 28 Sep 2004 21:28:58 +0100, Just zis Guy, you know? =

wrote:

On Tue, 28 Sep 2004 12:41:50 -0700, Slacker
wrote in message opse1yb0q7m83lxu@slacker:

Man, you guys can blow more wind than a Floridian hurricane!
When are you gonna blow out of town (or at least stop x-posting)?!?!?=
!

At a a guess, when the manufacturers stop selling a product with an
apparent serious fault, or produce some credible figures to prove that=

the apparent serious fault is not, in fact, an issue. Why?

Guy


Because you're sucking valuable brandwidth.

-- =

Slacker

On Tue, 28 Sep 2004 13:43:54 -0700, Slacker
wrote in message opse107gh3m83lxu@slacker:

Man, you guys can blow more wind than a Floridian hurricane!
When are you gonna blow out of town (or at least stop x-posting)?!?!?!

At a a guess, when the manufacturers stop selling a product with an
apparent serious fault, or produce some credible figures to prove that
the apparent serious fault is not, in fact, an issue. Why?

Because you're sucking valuable brandwidth.

Learn to use a killfile, or learn to tolerate people in an open forum
discussing relevant on-topic issues which are nonetheless not of
immediate interest to you.

Or go stick your head in a pig. I don't really care which.

Guy
--
May contain traces of irony. Contents liable to settle after posting.
http://www.chapmancentral.co.uk

88% of helmet statistics are made up, 65% of them at Washington University

Jobst Brandt

On Tue, 28 Sep 2004 21:54:23 +0100, Just zis Guy, you know? =

wrote:

On Tue, 28 Sep 2004 13:43:54 -0700, Slacker
wrote in message opse107gh3m83lxu@slacker:

Man, you guys can blow more wind than a Floridian hurricane!
When are you gonna blow out of town (or at least stop x-posting)?!?=
!?!

At a a guess, when the manufacturers stop selling a product with an
apparent serious fault, or produce some credible figures to prove th=
at
the apparent serious fault is not, in fact, an issue. Why?

Because you're sucking valuable brandwidth.

Learn to use a killfile, or learn to tolerate people in an open forum
discussing relevant on-topic issues which are nonetheless not of
immediate interest to you.

Or go stick your head in a pig. I don't really care which.

Guy


mmmmm... P I G ... I love them piggies!

Can I just do both :-P

Oh wait, Opera aint got no kill-file and their filters blow :-(
-- =

Slacker

Jobst says:



Absolutely nothing!

Is he usually this informative? ;-)

Steve

It seems that there are new participants reading this thread who do
not have a clear picture of what is being claimed and what forces are
causes by a typical front disc brake of a bicycle. I think the force
analysis can be clearly stated as follows:

Front wheels have a brake disc attached to the left side of the hub
rotating with the wheel. A caliper, attached BEHIND the left fork
leg, grasps the disc with friction pads to induce braking forces on
the disk.

Because the disc rotates forward with the wheel, its rearward portion
passing upward through the caliper, transmits and UPWARD force to the
caliper when braking. For hard braking, the magnitude of this force
can be derived from the ratio of the tire to disc diameter. This is
under the reasonable assumption that traction can achieve one-to-one,
(skid force equal to load) for clean pavement or soft firm soil
(knobby tires).

This upward force from the disc to fork leg is about four times
(tire-to-disc-diameter) the downward load on the fork, except that
this reaction force acts on only one side of the wheel. That is
(taking the caliper as the fixed reference), the left end of the axle,
on which the disc is mounted, is pushed downward with force of four
times the wheel load.

This separation force is alone not enough to dislodge the axle if it
is properly closed, however, braking can cause small downward movement
of the axle with every hard brake application and a subsequent upward
motion with downward loading. These small motions, like those of
retaining bolts of Shimano Octalink cranks or left pedal spindles with
right hand threads (some tandems) can unscrew the QR.

Once the QR is loosened or for that matter, initially not adequately
tight, the axle can be forced out of the retention ridge of the
dropout and cause the wheel to yaw and jam in the fork. This
generally causes the bicycle to pitch over forward with the rider.

This CAN occur because the caliper is mounted behind the fork leg
instead of in front, where this could not occur. This is the essence
of the complaint. That the wheel will separate is not claimed, only
that the possibility is inherent in this design that CAN permit such a
separation.

Because the fix (caliper in front) is so simple, the existence of this
design problem appears as a disregard for bicyclist's safety. All
arguments I have seen for not placing the caliper ahead of the fork
leg have been specious arguments at best, presented for reasons that I
do not understand.

Jobst Brandt




Jobst Brandt

Just zis Guy, you know? wrote:

The only thing I can't recall seing come loose is a
Nord-Lock washer set, and I bet even they will in the right (or wrong)
circumstances.


That still works because serrations on the top of the top washer lock it
to the nut rotation. i.e. it uses serrations to work just like a
Shimano skewer.

Tony

Stephen Baker wrote:
Jobst says:



Absolutely nothing!

Is he usually this informative? ;-)

He just likes using that sig to remind everyone he went to Satanford.

Bill "has chosen not to use a Maryland Alumni dot org addy, even AFTER we
won the national title in b-ball" S.

Just zis Guy, you know? wrote:
On Tue, 28 Sep 2004 06:44:07 -0700, jim beam
wrote:


James' proposed mechanism for
QR loosening makes sense from a mechanical perspective, and at the
very least needs to be properly followed up.


no, it _doesn't_ make sense from the mechanical perspective. just
because there is a resolved pullout force does _not_ mean it exceeds the
pullout force necessary to cause slippage, let alone ejection.


And that is precisely the question which I am saying should be
answered: does it exceed the pullout force, and if so, under what
conditions? But nobody with the wherewithal to test it seems terribly
interested in doing so.

i did the math on the pullout force with serrated axle face nuts. it
exceeds the resolved braking force by a factor of at last 3. please
post to forum if you have a different model.



have you
done the math for brake cable pullout? i mentioned this before but it
doesn't seem to have sunk in.


Have you tried riding a bike without a front brake? And without a
front wheel? I mentioned this before but it doesn't seem to have sunk
in.


bottom line, if the pullout force necessary to cause slippage [ignoring
lawyer lips] exceeds the resolved force of braking by a factor of 3 [and
that's a very conservative calculation, unlike the maximized braking
force calc] then this is all a wild goose chase.


You are begging the question. Who says it does? And even if it did,
to what extent can we rely on that given that there is a credible
mechanism advanced for the loosening of the QR under repeated heavy
braking?

what's the mechanism? all i see is locked skewers with 2 anti-loosening
devices that i've never seen budge in use.


So, unresolved questions. Being old-fashioned, my preferred solution
for unresolved questions is to set up some experiments.


Much more important than Cannondale's test is the test that many
thousands of riders do each day.


That's what DeHavilland said about the first few Comet crashes, IIRC.


you're well senior to me if you recall all that first hand.


Ah, so we are not allowed to know history, then? I used to volunteer
at a DeHavilland museum.

you said "iirc". picking nits, that implies you recall the
investigation, not that in a subsequent decade you heard the outcome of
the investigation.

dude, just so you know, volunteering there is /totally/ cool. i really
envy you being able to do that! do they have a mosquito there? truly a
wooden wonder.



failure analysis is all about omissions. in the comet case, it was
omission of research into all the stress concentrations caused by a
relatively small window corner radius in conjunction with a pressurized
fuselage.


Precisely. And in this case it's omission of tests of repeated heavy
braking on a fork / dropout whose geometry was clearly designed for
rim brakes and has not been reworked for the different forces involved
in disc brake use. Nobody thought to check. It's very obvious from
the initial reactions that nobody thought to work out the resultant
force. Having been prompted to do so they are now relying on the fact
that skewers are "obviously" not going to come undone. But "obvious"
things have a habit of being wrong, and no amount of Usenet discussion
will substitute for a realistic test. I am perfectly prepared to
admit that such a test may well show that only a fork such as James',
where the dropout was almost in line with the effective force of the
disc brake, is ever likely to be affected. I'd be quite happy with
that, since I ride a disc-braked bike every day. Until then I'm gogin
to be very paranoid about testing my QR.


in this case, we have one side of
the equation, the resolved braking force, and the other, the force
necessary to cause slippage. this latter has been ignored - a
rudimentary omission. the /real/ debate is whether this omission was
selective to further some other agenda.


The force required to cause slippage has not been ignored by James,
and not by me either. Who are you saying is ignoring it?

Guy

well, as i understand the argument, it goes like this:

resolved "ejection" force is postulated to be 1825N, and iso pullout
spec is alledged to be only 500N, therefore the sky will fall tomorrow.

what's being ignored is that a conservative estimate for pullout force
based on just part of one face of a serrated axle [what all disk brake
hub manufacturers afaik use] is in excess of 5000N. and that's /not/
including any effect of serrated skewer nut facings either. if that's
not ignoring a critical part of the analysis, i don't know what is.