Carlton Reid on QR safety

Or you could just mount the caliper on the leading side of the fork
and eliminate the need for the discussion entirely.

In article
,
"Clive George" wrote:

"Michael Press" wrote in message
...

Please comment upon the force diagram for front disc brakes.

I am neither a physicist nor engineer; many here are.

I will leave comments to those more qualified.

You owe it to yourself to see for yourself.

Micheal, you seem to be confusing comment with understanding. Understanding
the force diagram is easy enough. Being able to comment on it in a useful
manner, especially without repeating what has already been said, is entirely
different.

Or do you feel "me too" is an acceptably useful post?

Some folks are adamant that there is not a problem; but
never address the force diagram, and its consequences.
Being able to comment upon it in a useful manner is a
prerequisite to productively entering this discussion.

--
Michael Press

In article
pan.2006.02.06.12.13.39.502443@firstnamelastname. com.inva
lid,
Mike Causer wrote:

On Mon, 06 Feb 2006 04:12:58 +0000, Michael Press wrote:

You owe it to yourself to see for yourself. Jobst Brandt has already
posted a clear word picture of what is going on. The braking force of the
disk caliper on the disk generates a force. At the fork tips the braking
force translates into a force on the axle in the direction out of the fork
tips,

This is correct if the caliper is behind the fork and the fork slots
are vertical.


and this force is opposed only by the clamping of a quick release
on the fork tips.

Incorrect. There is the weight of the bike and rider as well.

The weight of the bike is there. True. Braking force plus
vibrations of rough trails where the amount of rider
weight taken up at the axle-fork tip interface varies
wildly means that the quick-release clamp frets and the QR
nut loosens through fretting. Many riders have reported
consistent loosening or QR nuts. The nut loosens, and soon
there is not even that holding the wheel in the fork tips.

--
Michael Press

In article ,
Tony Raven wrote:

Mike Causer wrote:
On Mon, 06 Feb 2006 04:12:58 +0000, Michael Press wrote:

You owe it to yourself to see for yourself. Jobst Brandt has already
posted a clear word picture of what is going on. The braking force of the
disk caliper on the disk generates a force. At the fork tips the braking
force translates into a force on the axle in the direction out of the fork
tips,

This is correct if the caliper is behind the fork and the fork slots
are vertical.


Wrong. Provided the caliper is not mounted in line with the centre line
of the fork slot there will be a component of the force along the centre
line of the slot. If the caliper is behind the centre line the force
component will be out of the slot, in front and its into the slot.

No one has yet commented on how the QR gets over the lawyers lips
without anyone noticing how loose the wheel has become in the forks and
the disc rubbing on the pads as the wheel flops from side to side.

Loosening of the quick release nut from brake forces and
rough terrain vibration. The quick release clamp is not
designed for these conditions.

--
Michael Press

Michael Halliwell writes:

Anyways, I think that checking the front quick release before each
ride might be a good idea. In fact, I think I'll go check it right
now...

You mean, like most manufacturers recommend before each ride in
their owners manuals?

What a novel concept!

That is "novel" if you mean that literally, as in "new". In the many
years I have ridden bikes with QR hubs, I have not done that and also
never found a loose QR when taking a wheel out for, for instance
repairing a flat on the road. Maybe the QR's of today are no good and
open themselves, as John Howard claimed in his now famous testimony
that brought us lawyer lips.

This is all so reminiscent of AUDI unwanted acceleration, that was an
old story long before because AARP folks driving Cadillacs had a
history of stepping on the gas when they meant the brake... so today
we must push the brake pedal before engaging the automatic
transmission. Not a bad idea, but useless for drivers with good
habits.

Jobst Brandt

In article ,
Werehatrack wrote:

On Mon, 06 Feb 2006 04:17:22 GMT, Michael Press wrote:

There are many people who do not crash an are constantly
retightening the quick release nut. It loosens under load
and vibration for which it is not designed.

True or False? You know the results of the free body
analysis and say that it is not a problem.

I have heard of this, but I have never encountered it on either of my
QR-equipped disc-front-brake bikes. I have asked a few other
disc-using riders around here if they have had this problem; none have
experienced it. I will point out that my sample is at least an order
of magnitude away from statistically significant, but as I said, it's
hard to convince people that there's a problem when they aren't having
it...and it's obvious to me that there is at least a good chance that
many (if not most) disc brake users are, in fact, neither aware that
there is even an issue being raised, nor having any problems that
would lead them to suspect one.

This does not mean that a convincing and repeatable demo would not
change their opinion. Look what happened with Kryptonite locks when a
certain video hit the net, despite the fact that it later turned out
that lots of the locks were not openable via the exploit. It is not
necessary for a problem to be a clear and present hazard for everyone,
it is merely necessary for them to *believe* that it is. So far, the
evidence for wheel ejection as a common hazard is entirely too scant
and academic, and does not fit with what the users see. *Show* them
the problem in a repeatable manner that reflects on an actual usage
scenario of some sort, and they will probably believe that it's
serious and that it needs to get fixed *right now*. Otherwise,
they're likely to dismiss it as another bunch of alarmist hand-waving.

You have not commented upon the free body diagram.

--
Michael Press

Mike Causer wrote:

On Mon, 06 Feb 2006 04:05:23 +0000, jobst.brandt wrote:

I am not questioning the direction of the load, what I _am_ questioning
is its magnitude in relation to the other loads present. To find the
value of the ejection force and the value of the retaining forces we
need to know the geometry of the whole bike and rider.

I don't see why. All that is required is what I stated, the ratio of
disk diameter to tire OD and the position of the caliper. The fore that
the caliper puts on the fork relative to the wheel is as I stated, only
caliper location is the matter at hand.

Except that there is a maximum force that be generated in this way, and
to find the maximum we need to consider the factors I've mentioned.

Assuming a conventional upright bike, with wheelbase a little over 1
metre, the maximum braking effort is found when the back wheel lifts, at
which point the retardation will be about 0.65g.

You don't think you can momentarily spike the braking force above that
without doing an endo?

(I don't know if you can, or by how much, but the point seems to have been
neglected).

--
Benjamin Lewis

Now is the time for all good men to come to.
-- Walt Kelly

James Annan wrote:
Tony Raven wrote:


No one has yet commented on how the QR gets over the lawyers lips
without anyone noticing how loose the wheel has become in the forks
and the disc rubbing on the pads as the wheel flops from side to side.


By Jove, Tony, I think you've got it! In 3 years of this "debate",
no-one has yet mentioned this critical and obvious point! What were we
all thinking of?

Sheesh. That's a truly lame attempt at denial, even by your own standards.

James

by jove, james, that's a really weak and pathetic denial of a pertinent
and obvious point! truly lame, even by your own standards.

Michael Press wrote:
In article ,
Tony Raven wrote:


Mike Causer wrote:

On Mon, 06 Feb 2006 04:12:58 +0000, Michael Press wrote:


You owe it to yourself to see for yourself. Jobst Brandt has already
posted a clear word picture of what is going on. The braking force of the
disk caliper on the disk generates a force. At the fork tips the braking
force translates into a force on the axle in the direction out of the fork
tips,

This is correct if the caliper is behind the fork and the fork slots
are vertical.


Wrong. Provided the caliper is not mounted in line with the centre line
of the fork slot there will be a component of the force along the centre
line of the slot. If the caliper is behind the centre line the force
component will be out of the slot, in front and its into the slot.

No one has yet commented on how the QR gets over the lawyers lips
without anyone noticing how loose the wheel has become in the forks and
the disc rubbing on the pads as the wheel flops from side to side.


Loosening of the quick release nut from brake forces and
rough terrain vibration. The quick release clamp is not
designed for these conditions.

it's nylocked /and/ serrated, therefore it /is/ designed to resist
vibration.

Tim McNamara wrote:
Or you could just mount the caliper on the leading side of the fork
and eliminate the need for the discussion entirely.

no tim, it's bad deployment of both fork material and caliper material.
compressive force [rear mounting] is much safer. which is why it's done.