Carlton Reid on QR safety

On Mon, 06 Feb 2006 05:53:44 -0800, David Martin wrote:

Except that it is perfectly possible to set up a *stationary* bicycle such
that increases in rider weight will increase the ejection force.

Sure, make the dropout point anywhere _above_ the horizontal.


As soon as the contact patch moves behind the
brake, the riders weight adds to the ejection force.

As the contact patch moves either forward or backward from directly under
the spindle the anti-ejection force due to weight of rider + bike will
diminish until it becomes zero when the contact patch is horizontal with
the spindle. As this force diminishes so does the braking power
available, until it also becomes zero when contact patch is horizontal.



Mike

Quoting Andy H :
Life sucks and **** happens, our (my anyway) pastime is rife with risk.

That doesn't really create a desire for extra risk without any extra fun.

If
the design is inherently flawed why have we not all been maimed by our
disk/qr problems?

Hyperbole. A design can be unsafe relative to other designs without the
failure rate being such as to injure every user.
--
David Damerell Kill the tomato!
Today is Olethros, February - a weekend.

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.
--
Typoes are a feature, not a bug.
Some gardening required to reply via email.
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Mike Causer wrote:
On Mon, 06 Feb 2006 05:53:44 -0800, David Martin wrote:

Except that it is perfectly possible to set up a *stationary* bicycle such
that increases in rider weight will increase the ejection force.

Sure, make the dropout point anywhere _above_ the horizontal.


As soon as the contact patch moves behind the
brake, the riders weight adds to the ejection force.

As the contact patch moves either forward or backward from directly under
the spindle the anti-ejection force due to weight of rider + bike will
diminish until it becomes zero when the contact patch is horizontal with
the spindle.

It is zero for a *stationary* bike when the contact point is under the
brake. As the patch moves behind the brake then the force becomes
negative (ie there is a pivot around the brake.)

Draw a line normal to the forces and plot on that line the force
applied to each point. That from the contact point is upward. That from
the brake is downward. The turning moment observed will show you that a
riders weight can provide an ejection force.


As this force diminishes so does the braking power
available, until it also becomes zero when contact patch is horizontal.

Indeed, but if the brake is binding than the available force is neither
here nor there as long as the rider is still staying behind the CoG.

...d

"James Annan" wrote in message
oups.com...

Jay Beattie wrote:
James Annan wrote:
Carlton Reid has a puff piece about a new "Secure QR
system" on bikebiz:
http://www.bikebiz.co.uk/daily-news/article.php?id=6427

While promoting this new mechanism as "safer" than the
existing system,
he also insists that "industry experts say QRs are safe,
when used
correctly".

This assertion is backed up with a quote from "industry
expert" Bob
Burns (actually Trek's *lawyer*), which is nothing more
than a
boilerplate denial dating to a few years ago when the
QR/disk issue
first surfaced.

Strangely, alongside this there is no space in his article
for these
quotes from people who actually have some relevant
engineering and
technical experience:

Gee, James, some pretty slick editing on your part,

_MY_ part? Did you not realise that the bikebiz article was
written by
Carlton Reid, not me?


This is a _direct_ cut and paste, completely unedited, from the
middle
of Carlton's article:

---
[...] industry experts say QRs are safe, when used correctly.

In 2003, Bob Burns, Trek's US-based General Counsel, told
BikeBiz.com:

The slick editing I am talking about is your post putting in the
bit about Bob Burns being Trek's *lawyer* and then leaving out
the part about how he has responded to your requests to look into
the problem (quote from Singletrack):

Trek's legal eagle in the USA has told BikeBiz.co.uk he will
"definitely talk to the relevant vendors and take a look at this
issue." What's needed are lab tests but even the proponent of the
wheel pop-out theory doesn't believe the supposed problem can
always be replicated away from the dirt. So, is it just a problem
with Ti skewers and badly-angled drop-outs, a problem easily
solved, or should bike trade execs be banging tech-heads together
to find out if the problem is more widespread?


Bob Burns, Trek's US-based General Counsel, has read the BikeBiz
story from earlier this week and has agreed to investigate
Annan's theory further. Trek is the first major company to agree
to such an undertaking.

Burns reports that the Trek warranty department has had no
reports of the kind of equipment failure described by Annan, the
Scottish climate research scientist, based in Japan.

However, Annan says the problem he describes is usually
mis-diagnosed as 'pilot error', in other words riders not
fastening their QRs correctly. Because of the mis-diagnosis risk,
Burns agreed to probe.

"Trek has not seen this, but [we] will be making inquiries of the
relevant component manufacturers," Burns told BikeBiz.co.uk.

"Virtually all 'defective quick release' claims that I have seen
relate to an improperly used quick release. Either the consumer
has ridden with the QR open; ridden with the QR losed like a wing
nut (rather than closing it over the cam); or ridden with
insufficient ightness to the adjusting nut to engage the cam. You
can generally determine this by examining the dropout surfaces,
which will show the marks left behind as a consequence of he
loose clamp force.

"We take great pains in our owner's manual to explain how to use
a QR, as do most good cycling books."

Annan says this is all well and good for rim-brake set-ups but QR
skewers may not be strong enough for disc-brake equipped bikes
pushed hard and fast by enthusiast riders.

(end quote)

The tone of your post is that there is some, sinister conspiracy.
You should give the complete story and disclose that Trek
actually listened to you. -- Jay Beattie.

On 5 Feb 2006 22:47:12 -0800, "James Annan"
wrote:

Werehatrack wrote:

It is very hard to convince people that a problem is both real *and
serious* when you don't have anything but math and a few isolated
phenomena to offer as evidence. That the problem is real they may
accept if they are math-literate, but since nearly everything has risk
of one sort or another, it's also necessary to convince them that the
problem is serious enough (not just in terms of potential harm should
it occur, but more specifically in terms of the potential for the harm
to come *to them* at all) before they will be persuaded that action is
warranted or necessary. The paucity of demonstrated failures speaks
volumes to the masses.

Do you think that Shimano were wrong to recall their brake cables?

http://www.bikebiz.com/daily-news/article.php?id=4933

----
A statement from Shimano said:

"It is possible that the tensile strength of the joint between the
cable and the cable end (nipple) may not meet Shimano's usual standards
and that therefore the nipple, when under stress during application of
the brake, could pull loose or detach from the cable. This could lead
to brake failure.

"Shimano is not aware of any case in which the nipple has separated
from one of these cables during use on a bicycle."
----

Note that not only was there not a single injury as a result of this
fault, there wasn't even a single failure in use. Numerous recalls are
made on a similar basis - this was just the first I googled. I question
whether you are aware of the relevant laws on the matter.

This was an example of a readily replicatable and demonstrated
shortcoming in a product. Shimano acted correctly even though no
in-service failures were on record.

The problem with the brake ejections is that as far as I have been
able to discover, no one has yet produced a method of demonstrating
the failure mode. When a failure is intermittent and not readily
reproducible, it is not yet considered to be fully understood, and
acting on what is at this point merely a combination of a small number
of unexplained incidents and an academic analysis showing *one
possible* factor (which remains just a possible factor until the
connecion is physically demonstrated) is not considered proper.
People in the product safety field would likely point out that further
analysis might demonstrate that the ejections resulted from a third
factor that has not yet been identified, and may show that this third
factor is the more serious one in need of attention. Consumer product
safety regulators despise acting before they are certain of what is
wrong, how it fails, and what needs to be done. This is not like
aviation safety, where the FAA has a mandate to ground a class of
aircraft if a fault is suspected and is not yet understood. Here, the
burden is the other way; no one will act until the fault is proven
*and* understood. The lack of a demonstrably repeatable failure mode
means that it's not proven that the failure is adequately understood.
If it was understood, the means of repeatably demonstrating it would
be apparent.

From a product liability standpoint, there are so many manufacturers
involved, supplying such a range of forks, wheels, brake assemblies
and quick releases, that I doubt that anything short of a real, live
demo is going to spur them to action either. In point of fact, no
single manufacturer produces the entire system, making it very
difficult to even get the manufacturers to get together and look at
the issue; each is likely to view it as "somebody else's problem".

The best bet for getting action is still to put together a repeatable
demo that shows the failure. With that in hand, published to the web,
I suspect that the action would be swift. If it's not possible to
demonstrate the problem, a much larger number of in-service failures
will have to be accumulated (and will have to span a much broader
cross-section of the riding public) before anything will happen.
--
Typoes are a feature, not a bug.
Some gardening required to reply via email.
Words processed in a facility that contains nuts.

On 06 Feb 2006 15:22:28 +0000 (GMT), David Damerell
wrote:

Quoting Andy H :
If
the design is inherently flawed why have we not all been maimed by our
disk/qr problems?

Hyperbole. A design can be unsafe relative to other designs without the
failure rate being such as to injure every user.

The stated attitude, however, is at the root of the problem. To
convince someone of a risk, it must be presented to them in terms that
they can understand, and it must look like something that could
actually be a problem *for them*. Thus far, I have to say that the
evidence for wheel ejection as a problem for the average rider is much
too thin to be compelling. One good, repeatable demo could change
that. I doubt that anything else will.
--
Typoes are a feature, not a bug.
Some gardening required to reply via email.
Words processed in a facility that contains nuts.

Mike Causer writes:

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. The
friction coefficient tyre-ground needs to be 0.65 or better. Higher
friction won't gain any more retardation. At this point the whole
of the weight of bike and rider is carried by the front axle,

Forget about the back wheel. I said that when the front wheel skids
on good traction (which my be rear wheel lift-off) the forces are
simply front wheel related and rider position etc. have no bearing.

Jobst Brandt

In article ,
says...

Holes in the current disks reduce surface area and do nothing positive
for cooling. As I mentioned earlier, the holes seem to be a holdover
from auto drum brake mystique.

I thought the holes were there to attract all the weight weenies. At
interbike there was a company selling custom brake rotors with all sorts
of cut outs.
-------------
Alex

On Mon, 06 Feb 2006 14:00:36 +0000, 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.

OK, my comment is a special case of your general case. However as the
majority of drop-outs are pretty close to vertical I hope it's a
simplification we can live with.



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.

I thought somebody did, but maybe that was in another of the interminable
threads about this. If I ever got a bike with lawyer lips I'd grind the
damn things off anyway.


Mike