Carlton Reid on QR safety

In article ,
Helen Deborah Vecht wrote:

"Andy H" typed



"Richard" wrote in message
...
Snip -
......but as I neither sell, use, maintain, nor have any access to disk
brakes or QR axles, I could add nothing useful to the debate.

R.
Then do just that, you have no potential problems do you? Do you have the
statistics to hand?

Andy H


The problem is not statistical.

The problem is anecdotal.

Many here in the UK will know of a single catastrophic event that might
have been the result of wheel ejection.

A single catastrophe does not a statistic make but it does not mean
there is not a problem.

That IS the problem.

Please comment upon the force diagram for front disc brakes.

--
Michael Press

On Sun, 05 Feb 2006 04:46:49 GMT, Michael Press wrote:

In article ,
"Andy H" wrote:

"David Martin" wrote in message
oups.com...

Werehatrack wrote:
Those of us who have seen your prior postings about the issue of disc
brake ejections are fully aware of your position on the matter. Is it
possible for you to accept the fact that for the majority of the
readers, the evidence thus far published is not persuasive that there
is a serious problem here which is not related to user error?

Why do you claim to speak for the majority of readers, most of whom
have expressed no public opinion on the matter?

..d

Does the fact that the majority of people have expressed no public opinion
(read; interest) speak volumes as to the severity of the problem? Do YOU
know the relevant statistics to say that this is a major problem or design
flaw?

Life is inherently risky and I for one would rather check my qr's before a
ride and have disk brakes than try to do what I do with rim brakes.

I draw inferences from the fact that those who claim there
is no problem refuse to comment upon the force diagram.

You confuse inaction with refusal; they are not the same.

Thus far, the number of incidents documented for which no user error
could be identified is small, and there has been no analysis that I've
seen showing that the rate of failure varies from what is found on
non-disc-brake bikes. Yes, the force diagram indicates that a force
can be present which could lead to this event, but the fact remains
that in the direct experience of the majority of disc-brake-equipped
riders, this force does not have the described effect. Their wheels
are not leaping out, and their brakes are, in the main, stopping them
safely and surely; as a result, they have a hard time seeing that
there's a problem here.

To make matters worse, this is not like the flaming Pinto syndrome, in
which the result was easily duplicated in a test setting. Of course,
as far as I can tell, no one seems to have tried to duplicate the
wheel ejection event in a lab, either, or if they have tried, perhaps
the results have not been conclusive or predictable; I haven't seen
results published in any event.

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.

Most of the reason I'm taking this position is that it is essential,
if the problem is to be addressed, for those advocating change to
understand that the task is not merely to show that something *can*
occur, but that it is *likely*, and most importantly to demonstrate
when, and how, that event is most likely to take place so that a
genuinely repeatable demonstration of the risk is possible. Ford did
nothing about the Pinto fuel tank until the crash test film was shown
on national TV...and the Pinto was a popular car, with a large number
of users who were potentially at risk. Bikes with disc brakes are not
all that common to begin with, and a flaw in them will be of direct
concern to fewer people, so the proponents of change will have to work
even harder to develop a compelling argument in favor of mandatory
action before the existing and potential consumers can be reached and
convinced that they should not buy or use the product until the design
has been made resistant to the described fault.

As is true for most things, the majority responds only to those things
that they both understand and believe are important to them. They
remain silent when they are confident that they and their interests
are not directly at risk. Thus far, they have been silent on the
subject of disk ejection; most are probably unaware of the issue, in
my opinion, and this reflects the lack of interest by the news
dissemination channels, for whatever reason. But before it will be
possible to get the word out, a much stronger case will need to be
built, and the seriousness of the risk will need to be much more
reliably demonstrable than it is at present.


--
Typoes are a feature, not a bug.
Some gardening required to reply via email.
Words processed in a facility that contains nuts.

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:

to which the response may as well be: "strangely, there's no space in
this article for any evidence of this supposed disaster ever being
attributable to anything other than inability to use a q.r."


---
Chris Juden, Technical officer, CTC:
"It's not just scaremongering, but all hangs together and makes perfect
sense. In fact I'm kicking myself for not thinking of it before."

strange how he hadn't noticed disk brakes ejecting /before/ reading
chicken littles tale of doom...


"changes must be made to the way disk brakes and front wheels are
attached to forks"

Jobst Brandt, author, "The Bicycle Wheel":
"The more I see on this the more I find the defense of the status quo
stranger than fiction. Why are writers trying to say that it can't
happen? What motivates writers to claim that disc brakes as currently
offered are not a hazard?

as above, how are we not swamped with reports of ejected disks here on
r.b.t? the chicken littles, would /LOVE/ to jump aboard if ejection was
actually an occurrence.


The mechanism has been clearly stated, the forces have been identified
in magnitude and direction, and credible descriptions of failures have
been presented. What's going on here! There is no easter bunny.
Believe it!"

i'll believe it when i see it. i've been riding disk 3 years - never
any slippage or ejection. and i still ask among others i meet with
negative results. strange how reality seems to be so easily discounted
around here.


John Forester, author, "Effective Cycling":
"All that I can say is gross negligence."

another one suckered into the hysteria.


Unnamed Marzocchi Tech Support:
"It is recommended that an 8" rotor is not used on a standard axle fork
because the forces exerted on the wheel can potentially pull the axle
out of the dropouts."

un named? that's credible james. especially when force is /less/ for
an 8" disk compared to 6".


Brant Richards, On-One:
"From the next batch, our rigid forks will have dropouts which are
angled forward at 45degrees or thereabouts.

This is because when I was coming home, and pulling a stoppy outside my
driveway, I kept finding the front wheel shifted in the dropout."

and his axle faces were serrated? and his dropouts were made of what?


Dave Gray, Surly:
"You are correct. I've noticed the problem on my Karate Monkey fork."

as above, steel fork.


Ben Cooper, Kinetics, describing his experiment:
"Conclusion: From the above, there seems to be an effect from the disc
brake which causes the quick release to loosen."
---

eh? "loosening" is not slippage or ejection.



And even more strangely, although he mentions the ongoing Walmart case
concerning children's bikes, and refers repeatedly to user error, he
also didn't find space to mention the recent out of court settlement in
which a manufacturer paid off an (experienced adult) rider who was
seriously injured by a front wheel ejection on a disk+QR fork.


James

bottom line, we still have yet to see any disk brake ejection. james,
you get 10 points for effort in trying to create this storm, but alas,
your teacup of evidence is bone dry. stick to climatology if you want
to keep your name in the headlines - this is a q.r. user competency
issue, not a disk brake design issue. what's next? the crusade against
fundamentally unstable two-wheelers?

jim beam wrote:


bottom line, we still have yet to see any disk brake ejection. james,
you get 10 points for effort in trying to create this storm, but alas,
your teacup of evidence is bone dry. stick to climatology if you want
to keep your name in the headlines - this is a q.r. user competency
issue, not a disk brake design issue. what's next? the crusade against
fundamentally unstable two-wheelers?

Fundementally, it's all about James' ego. That's why he busts out his
yawn-inducing troll every four months or so.

Funny thing - no movement at all in my Shimano XT QR on Marzocchi
Flylight 80. Commuter with slicks - lots of hard, high-g braking.
Lever got closed at about 80 degrees, which is a little less than
normal for me.

His chatter, along with the sycophantic "me toos", seems to have no
effect on the ability of the QR to do its basic function. Heh.

E.P.

jim beam wrote:

i'll believe it when i see it. i've been riding disk 3 years -

Clearly you're one of the many who don't need disks riding nothing
off-road but the wimpier trails of Marin.


bottom line, we still have yet to see any disk brake ejection.

So what happened to Russ Pinder, someone who knows how to tighten a QR
and checked his before his fateful ride? You're really offensive with
your adamant refusal to acknowledge the failures that have happened.

Greg
--
"All my time I spent in heaven
Revelries of dance and wine
Waking to the sound of laughter
Up I'd rise and kiss the sky" - The Mekons

jim beam wrote:

James Annan wrote:

Brant Richards, On-One: "From the next batch, our rigid forks will have
dropouts which are angled forward at 45degrees or thereabouts. This is
because when I was coming home, and pulling a stoppy outside my
driveway, I kept finding the front wheel shifted in the dropout."

and his axle faces were serrated? and his dropouts were made of what?

What clamping force did he apply to the QR? Was it perhaps less than it
should have been due to poor lubrication? What was the geometry and centre
of mass of the bike+rider+panniers? What is the maximum instantaneous
braking force it is possible to apply for this configuration?

No thanks, I'll stick to a design that doesn't rely so heavily on so many
unknowns and variables. Adding serrations to directly resist pullout of a
critical component is not good design, it's a kludge required to make a
fundamentally flawed design work most of the time. See if you can find a
qualified mechanical engineer who disagrees.

--
Benjamin Lewis

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

Michael Press typed



The problem is not statistical.

The problem is anecdotal.

Many here in the UK will know of a single catastrophic event that might
have been the result of wheel ejection.

A single catastrophe does not a statistic make but it does not mean
there is not a problem.

That IS the problem.

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.

--
Helen D. Vecht:
Edgware.

On Sun, 05 Feb 2006 20:31:15 +0000, Michael Press wrote:


Please comment upon the force diagram for front disc brakes.

Are there any besides Annan's hand-drawn on a photo?

That one omits the vertical load the forks put on the spindle, which at
maximum braking effort will be weight of the rider plus ( bicycle minus
front-wheel) .


To eject the spindle the force trying to do so from the geometry of the
brakes will need to be greater than that vertical load _plus_ the
frictional force from the clamping of the spindle -- be it QR or hex
nut. To do the calculations you need to know the coefficient of friction
between tyre & road, and the location of the Centre of Gravity of the
rider+bike combination as well as the location of the brake pads,
the front wheel & brake diameters, and the wheelbase.

Because the CoG of recumbents is somewhat lower than an upright, the
braking forces can be greater (10-15% -- not as much better as some
believe) so I would expect a genuine problem to turn up first on
disk-braked 'bents. I've been reading the HPVA mailing lists and
alt.rec.bicycles.recumbents for many years and don't remember seeing this
problem mentioned. OTOH, maybe 'bent riders know how to do up a QR
properly.



Mike

Mike Causer writes:

Please comment upon the force diagram for front disc brakes.

Are there any besides Annan's hand-drawn on a photo?

That one omits the vertical load the forks put on the spindle, which
at maximum braking effort will be weight of the rider plus ( bicycle
minus front-wheel) .

To eject the spindle the force trying to do so from the geometry of
the brakes will need to be greater than that vertical load _plus_
the frictional force from the clamping of the spindle -- be it QR or
hex nut. To do the calculations you need to know the coefficient of
friction between tyre & road, and the location of the Centre of
Gravity of the rider+bike combination as well as the location of the
brake pads, the front wheel & brake diameters, and the wheelbase.

You can isolate the forces of interest more simply by noting the ratio
of wheel OD to brake disk diameter and from that assess forces
(assuming a traction coefficient of one, which is appropriate for
knobby tires on stiff clay or road tires on dry pavement). The rear
portion of the disk rotates upward through the brake caliper that
stops the wheel and thereby receives an upward force of wheel:disk
ratio times the load on the wheel, even tough the downward force on
the dropout is only half the wheel load, each dropout carrying half
that load.

I think that calculation accurately states the problem and should make
apparent why this is a bad design. Forget about GC and other
calculations that muddy the straight forward relationship between
downward and upward forces on the dropout in question. I think
caliper position is an obvious main item for discussion.

Jobst Brandt

Werehatrack wrote:
On Sat, 04 Feb 2006 13:24:51 -0800, "G.T."
wrote:

David wrote:
James Annan wrote:

Werehatrack wrote:

Those of us who have seen your prior postings about the issue of disc
brake ejections are fully aware of your position on the matter.



However, those who read Carlton's article on Bikebiz might think it
safe to draw the conclusion that "industry experts say QRs are safe,
when used correctly", even though numerous industry experts have quite
clearly expressed the contrary view.

They will also not know that one case was recently settled in favour
of the rider.

James


Out of court settlements almost always include a statement that the
plantiff is not admitting liability. It is often less costly to pay a
small settlement than it is to defend the claim, particularly if the
jurisdiction is known to be plaintiff-favorable.

That first plantiff should be defendant.

True, as is the statement so amended.

And in fact, in most such cases, getting an out-of-court settlement
also has two other beneficial results for the defendant; it ends the
case completely without any opening for it to continue through some
sort of appeal, and it precludes the possibility that the case can be
used as a precedent. Given the combination of cost of defense, the
possibility that the suit might initially be lost (and thereby often
bring on a spate of me-too suits), the hazard that the defense expense
might dwarf the actual settlement if an appeal is (or must be) filed,
and the hazard that the finding might be cited in other cases as a
precedent, there's lots of reason to shut down the process by making
an offer to settle even when the case isn't necessarily all that
strong for the plaintiff.

The fact is that most cases settle -- except med mal, where the
consequences of settlement are significant (doctor gets reported to
national registry, premiums go through the roof), and the chances of
winning generally are high. Notwithstanding what you read in the news,
it is the rare case when a plaintiff wins a med-mal case. Products
cases -- even big ones -- usually settle unless there is an
exceptionally low chance of liability or the probable award is way
lower than plaintiff's demand. Also, some companies just try
everything, and some companies settle everything. Toro -- the lawmower
company -- puts everything into mediation. Make a claim, go to
mediation.

In some states, the impetus to settle is being reduced by
defendant-friendly changes to statute, often made under the guise of
"ending lawsuit abuse". Sometimes, what's billed as an abuse-control
measure turns out to be a PLI-defense attorney's nightmare...because
the defense lawyers don't get paid the big bucks for doing the
slam-dunk early dismissal filings, they only make the big bucks when
the case goes on long enough to rack up some worthwhile billable
hours.

You have been reading too many Grisham novels. Every time some tort
reform package is put together, it usually gets smushed like a bug. All
I see are statutes creating new claims for relief and not ending them,
particularly in the employment field.

Look for subtle and stealthy moves by PLI defense attorneys, and more
open ones by plaintiff lawyers, to get plaintiff-friendly changes made
if their billable hours drop too low. They both have a vested
interest in keeping the process alive.

There is very, very little legislation proposed by defense lawyers, and
most of that is "law improvement" legislation, e.g., clarificaiton of a
poorly drafted statute or process-related changes like amending the
rules of civil proceedure. Most all of that is done on a bi-partisan
basis. Most of the defense-friendly tort reform legislation is proposed
by industry or professional organizations including the AMA and the
Chamber of Commerce. On the other hand, ATLA and some of the
plaintiff's attorneys groups do propose or oppose legislation more
vigorously -- which generally means a welter of Erin Brockovich
commercials until the legislation passes or fails. -- Jay Beattie.