Carlton Reid on QR safety
James Annan
<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:
---
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."
"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?
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!"
John Forester, author, "Effective Cycling":
"All that I can say is gross negligence."
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."
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."
Dave Gray, Surly:
"You are correct. I've noticed the problem on my Karate Monkey 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."
---
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
--
James Annan
see web pages for email
http://www.ne.jp/asahi/julesandjames/home/
http://julesandjames.blogspot.com/
Werehatrack
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? Merely
casting aspersions on an announcement because it contains a statement
of fact by an attorney (which no one represented as anything but what
it was) is not saying much about the subject.
--
Typoes are a feature, not a bug.
Some gardening required to reply via email.
Words processed in a facility that contains nuts.
David Martin
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
James Annan
> 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.
Tim McNamara
> 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?
All that would prove is that the majority of readers lack an adequate
understanding of science. Given how weak science education is in the
US, this is not a surprise.
The situation with disk brakes is very simple. It is a faulty design
that poses a danger to the people who use disk brakes. Current disk
brake designs cause an ejection force that canpush the front wheel out
of the dropout. There is no way for that the be refuted, although
once again the strange phenomenon of people defending bad design will
no doubt rear its head in this thread.
Tim McNamara
> 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.
Don't appeal to authority. Just state the facts, which are simple and
straightforward.
David
> 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.
jobst....@stanfordalumni.org
>> 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?
> All that would prove is that the majority of readers lack an
> adequate understanding of science. Given how weak science education
> is in the US, this is not a surprise.
> The situation with disk brakes is very simple. It is a faulty
> design that poses a danger to the people who use disk brakes.
> Current disk brake designs cause an ejection force that can push the
> front wheel out of the dropout. There is no way for that the be
> refuted, although once again the strange phenomenon of people
> defending bad design will no doubt rear its head in this thread.
Yes. So why is this kind response to technical failures so common, be
that valve stem separation, spoke failures, crank failures, stem
failures and many more. They seem so personal and vehement that one
would guess that the writers were the manufacturers themselves. I
sense a strong apologists tone in many of these.
Jobst Brandt
Andy H
"David Martin" <martin...@blueyonder.co.uk> wrote in message
news:1139061323.5...@z14g2000cwz.googlegroups.com...
(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.
Just my 2p
Andy H
Richard
> Does the fact that the majority of people have expressed no public opinion
> (read; interest)
Why do you read that? I have hitherto expressed no public opinion.
I've read James' webpages on the subject and found his hypothesis
interesting and convincing; I would have liked to investigate the QR
vibrational loosening in more detail, 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.
G.T.
And what if it happened after 3 hours of riding even when you checked it
before the ride?
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
G.T.
That first plantiff should be defendant.
James Annan
I'm only pointing out that Carlton's appeal to authority isn't even
honest, let alone correct. He knows that numerous industry experts
dispute what he wrote.
Andy H
"Richard" <ric...@nowhere.invalid> wrote in message
news:ds35qv$8q3$1...@nwrdmz01.dmz.ncs.ea.ibs-infra.bt.com...
Snip -
>......but as I neither sell, use, maintain, nor have any access to disk
>
> R.
statistics to hand?
Andy H
Andy H
"G.T." <getn...@dslextreme.com> wrote in message
news:11ua6ri...@corp.supernews.com...
> Andy H wrote:
>> "David Martin" <martin...@blueyonder.co.uk> wrote in message
>> news:1139061323.5...@z14g2000cwz.googlegroups.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 what if it happened after 3 hours of riding even when you checked it
> before the ride?
>
> Greg
>
the design is inherently flawed why have we not all been maimed by our
disk/qr problems? (As MV would no doubt wish :-).
We drive our cars with unsafe airbags and inherently flawed seat restraints.
Trains crash and so do planes. I'm not trying to be a troll here but should
we get some perspective on this.
Andy H
frkr...@gmail.com
Andy H wrote:
>
> Life sucks and shit happens, our (my anyway) pastime is rife with risk. If
> the design is inherently flawed why have we not all been maimed by our
> disk/qr problems?
As I understand it, it's because it takes particular circumstances to
make the failure likely - for example, repeated very hard braking,
especially on bumpy descents. Most riders do not encounter those
circumstances.
But those circumstances are part of the normal design conditions for
certain bikes. If a design injures a person who's using it in the
manner for which it was designed, there's a problem. The occurrence
doesn't have to be common for this to be true.
> We drive our cars with unsafe airbags and inherently flawed seat restraints.
> Trains crash and so do planes. I'm not trying to be a troll here but should
> we get some perspective on this.
I won't defend airbags. But I'll point out that when people are
injured by airbags, train or plane crashes, the law does not say "Oh,
get over it. You knew that shit happens."
- Frank Krygowski
Adam Rush
amazement at the fact that Annan is still posting here about it.
Tim McNamara
> I have come here not to express an opinion on the debate, but rather
> amazement at the fact that Annan is still posting here about it.
"Here" being which newsgroup or Web-leech portal?
And why would you be surprised? He has found a serious design flaw
and has detailed that flaw. It is up to the bike industry to correct
it. In the meantime, individuals need to have this information in
order to make an informed decision about whether to buy or use bikes
with this design flaw.
Werehatrack
>I won't defend airbags. But I'll point out that when people are
>injured by airbags, train or plane crashes, the law does not say "Oh,
>get over it. You knew that shit happens."
Actually, the law gets closer to exactly that every day. Read the
provisions recently enacted exempting the drug companies from class
action suits, and then explore the similar changes which are being
sought for other PLI issues.
Not that this is a fundamentally flawed attitude, in fact; there are
plenty of PLI lawsuits in which the plaintiff is really saying "I'm
too stupid to know what's dangerous, and I want you to pay for my
stupidity even though no one in their right mind would have done what
I did."
The balance has been swung too far in both directions in the past, and
the urge is always to swing the pendulum hardest from the side that is
currently most heavily burdened by it.
Werehatrack
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.
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.
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.
Johnny Sunset
Andy H wrote:
>
> Life sucks and shit happens, our (my anyway) pastime is rife with risk. If
> the design is inherently flawed why have we not all been maimed by our
> disk/qr problems? (As MV would no doubt wish :-).
Who is "MV"?
--
Tom Sherman - Fox River Valley
"They [hominids] ARE acceptable prey, ESPECIALLY mountain bikers."
- M.V.
"We are discussing whether humans as prey are 'natural'. Clearly,
they are, or that mountain lion wouldn't have been trying to eat a
human." - M.V.
"Abnormal would be a mountain lion speaking English." - M.V.
"Mountain lions have always eaten humans, throughout our evolutionary
history." - M.V.
Michael Press
"Andy H" <Oohd...@notagain.com> wrote:
I draw inferences from the fact that those who claim there
is no problem refuse to comment upon the force diagram.
--
Michael Press
Shawn
> Andy H wrote:
>
>>Life sucks and shit happens, our (my anyway) pastime is rife with risk. If
>>the design is inherently flawed why have we not all been maimed by our
>>disk/qr problems? (As MV would no doubt wish :-).
>
>
> Who is "MV"?
He who must not be named.
Mike Jacoubowsky
> 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.
"In 2003, Bob Burns, Trek's US-based General Counsel, told BikeBiz.com:
"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 closed like a wing nut (rather than closing it over
the cam); or ridden with insufficient tightness to the adjusting nut to
engage the cam."
=======================
Where, exactly, does the quote from Bob Burns say anything whatsoever about
your QR/disk issue? He's addressing only one thing in the quote given- quick
releases. Nothing about disk brakes.
For that matter, not one place in the article is anything said about brakes.
Just quick releases. And the timing and development w/regards Pacific
Bicycles implementing a new quick release design probably has everything to
do with the lawsuit they got hit with (quick releases supposedly failing in
the field on low-end kids bikes) and nothing to do with disk brakes.
--Mike-- Chain Reaction Bicycles
www.ChainReactionBicycles.com
"James Annan" <still_th...@hotmail.com> wrote in message
news:44jhcaF...@individual.net...
Simon Brooke
('ric...@nowhere.invalid') wrote:
> Andy H wrote:
>> Does the fact that the majority of people have expressed no public
>> opinion (read; interest)
>
> Why do you read that? I have hitherto expressed no public opinion.
> I've read James' webpages on the subject and found his hypothesis
> interesting and convincing
I've read James' web pages on the subject, and I've listened to other
people (Darth Ben for example) who have empirically verified James'
hypothesis. I ride a lefty off road. I did before I knew about this
problem, it has to be admitted. But if I did now convert back to a
conventional fork, it would have a through axle.
--
si...@jasmine.org.uk (Simon Brooke) http://www.jasmine.org.uk/~simon/
;; All in all you're just another hick in the mall
-- Drink C'lloid
Mike de Van Man
>> Who is "MV"?
>
>
> He who must not be named.
If you've never encountered worse on Usenet,
you've led a sheltered life.
--
Mike de Van Man
Shawn
> Shawn wrote:
>
>
>>>Who is "MV"?
>>
>>
>>He who must not be named.
>
>
> If you've never encountered worse on Usenet,
> you've led a sheltered life.
>
Helen Deborah Vecht
> 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?
I have expressed nothing on the subject as I have no relevant knowledge.
This does NOT mean I have no interest; I just try not to post if I have
nothing useful to add.
--
Helen D. Vecht: helen...@zetnet.co.uk
Edgware.
Helen Deborah Vecht
> 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.
Helen Deborah Vecht
YAM & IAY...
Michael Press
Please comment upon the force diagram for front disc brakes.
--
Michael Press
Werehatrack
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.
jim beam
> 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?
Ed Pirrero
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.
G.T.
>
> 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.
Benjamin Lewis
> 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
Helen Deborah Vecht
> >
> >
> > 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.
Mike Causer
> 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
jobst....@stanfordalumni.org
>> 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
Jay Beattie
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.
Mike Causer
> I think that calculation accurately states the problem and should make
> apparent why this is a bad design.
The racing car design world went through this in the 1970s when the
argument was that leading calipers loaded the hub bearings under braking
but trailing calipers unloaded the hub. So the effect is there without
doubt. For racing cars (and modern motorbikes) it turned out that brake
cooling was more important than bearing loads.
> Forget about GC and other calculations that muddy the straight forward
> relationship between downward and upward forces on the dropout in
> question.
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 think caliper position is an obvious main item for discussion.
If the caliper is forward of the axle it will not try to eject the
spindle, but it will obstruct cooling of the disc. If the caliper is
aft of the axle the cooling will improve, but it will try to eject the
spindle. If the cooling _is_ needed are the ejection forces outweighed
by the existing retention forces?
As I have not yet seen a bicycle brake disk that looked as if any effort
had been made to improve its cooling (funky slots don't do a lot [1]), I
suppose that brake overheating is not a significant factor in bike
brakes, so the short-duration loading on emergency stops should take
precedence and the caliper would preferably be to the front. If I
lived in the Alps instead of the Fens I might have a different view.
[1] Slots and holes take the "fire-band" off the pad material. To get
the pads that hot the disk will be glowing red. To have the slots
doing anything to cool the disk there needs to be an airflow _though_
them, which needs air ducts or some other method of moving air at right
angles to the direction of travel.
Mike
Jay Beattie
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,
> 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, too, being that the
quote from Bob Burns is three years old, and the last time around, he
was praised for being the only representative from a large manufacturer
who was willing to look into your claims. See
http://www.singletrackworld.com/article.php?sid=1005 . Also, there is
nothing sinister about Mr. Burns being Trek's *laywer*. General
counsel usually handles liability claims and knows what claims have
(and have not) been made. Imagine that -- no *conspiracy*.
Caveat: I am an evil defense lawyer. Oddly enough, me and my cabal of
evil defense lawyers here in Oregon -- land of some of the best
mountain biking in the world -- have yet to see a QR/disc brake claim.
Not that the design cannot be improved (a question I am not competent
to answer), but there is no plague of claims as far as I can tell. --
Jay Beattie
James Annan
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:
---
James
Tim McNamara
> I am neither a physicist nor engineer; many here are.
>
> I will leave comments to those more qualified.
The diagrams are so simple that you can understand the principles
involved and understand the issue, even if you can't do the math.
Take responsibility for knowing for yourself.
Tim McNamara
> On Mon, 06 Feb 2006 01:23:22 +0000, jobst.brandt wrote:
>
>> I think that calculation accurately states the problem and should
>> make apparent why this is a bad design.
>
> The racing car design world went through this in the 1970s when the
> argument was that leading calipers loaded the hub bearings under
> braking but trailing calipers unloaded the hub. So the effect is
> there without doubt. For racing cars (and modern motorbikes) it
> turned out that brake cooling was more important than bearing loads.
FYI that guy you're talking to designed suspensions for Porsche. He's
probably aware of that.
>> Forget about GC and other calculations that muddy the straight
>> forward relationship between downward and upward forces on the
>> dropout in question.
>
> 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.
You're muddying the waters unnecessarily. You need to know the
orientation of the force compared to the dropout slot, and the
difference between the distance from the axle to the braking surface
and from the axle to the tire contact patch. The first will tell you
whether the reaction force from braking will push the axle out of the
dropout; the second will tell you how much the force driving the wheel
will be multiplied. The smaller the brake disk, the higher the
mutiplication of force- so a wheel with a 6" disk will result in a
stronger ejection force that an 8" disk (a 26" MTB wheel being
actually about 24" in diameter, so the difference is 4:1 for a 6" disk
and 3:1 for an 8" disk).
The only number you need to add is how much force is resulting from
forward motion of the bike, and for that you only need velocity and
mass, not the rest of the stuff you're claiming is necessary.
>> I think caliper position is an obvious main item for discussion.
>
> If the caliper is forward of the axle it will not try to eject the
> spindle, but it will obstruct cooling of the disc. If the caliper
> is aft of the axle the cooling will improve, but it will try to
> eject the spindle. If the cooling _is_ needed are the ejection
> forces outweighed by the existing retention forces?
The caliper is behind for fork leg to protect it from hitting rocks,
bits of tree and undergrowth. The location has nothing to do with
cooling.
jobst....@stanfordalumni.org
>> I think that calculation accurately states the problem and should
>> make apparent why this is a bad design.
> The racing car design world went through this in the 1970s when the
> argument was that leading calipers loaded the hub bearings under
> braking but trailing calipers unloaded the hub. So the effect is
> there without doubt. For racing cars (and modern motorbikes) it
> turned out that brake cooling was more important than bearing loads.
>> Forget about GC and other calculations that muddy the straight
>> forward relationship between downward and upward forces on the
>> dropout in question.
> 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. You'll note this
requires no further information about rider position or other bicycle
dimensions.
>> I think caliper position is an obvious main item for discussion.
> If the caliper is forward of the axle it will not try to eject the
> spindle, but it will obstruct cooling of the disc. If the caliper
> is aft of the axle the cooling will improve, but it will try to
> eject the spindle. If the cooling _is_ needed are the ejection
> forces outweighed by the existing retention forces?
Well its about time we got rid of the silly holes in the disk and
realize that in most uses, there isn't much wind for cooling. It's
not as if we are talking about road bicycle descending from one
hairpin turn tot he next, coasting at high speed between.
> As I have not yet seen a bicycle brake disk that looked as if any
> effort had been made to improve its cooling (funky slots don't do a
> lot [1]), I suppose that brake overheating is not a significant
> factor in bike brakes, so the short-duration loading on emergency
> stops should take precedence and the caliper would preferably be to
> the front. If I lived in the Alps instead of the Fens I might have
> a different view.
> [1] Slots and holes take the "fire-band" off the pad material. To
> get the pads that hot the disk will be glowing red. To have the
> slots doing anything to cool the disk there needs to be an airflow
> _though_ them, which needs air ducts or some other method of moving
> air at right angles to the direction of travel.
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.
Jobst Brandt
Michael Press
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, and this force is opposed only by the
clamping of a quick release on the fork tips.
--
Michael Press
Michael Press
Werehatrack <rau...@earthWEEDSlink.net> 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.
--
Michael Press
Werehatrack
wrote:
>
>Werehatrack wrote:
>> 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.
You're not in Texas. Here, the trend is decidedly in the other
direction, with the effect that it's often difficult to get an
attorney to take a liability case on contingency anymore. The most
significant effect is that even a middle-income plaintiff may not be
able to afford to bring an action for recovery of damages against a
company.
Of course, Texas also has the most selectively gullible electorate in
the nation IMO.
jobst....@stanfordalumni.org
>>> I think that calculation accurately states the problem and should
>>> make apparent why this is a bad design.
>> The racing car design world went through this in the 1970s when the
>> argument was that leading calipers loaded the hub bearings under
>> braking but trailing calipers unloaded the hub. So the effect is
>> there without doubt. For racing cars (and modern motorbikes) it
>> turned out that brake cooling was more important than bearing
>> loads.
> FYI that guy you're talking to designed suspensions for Porsche.
> He's probably aware of that.
Yes but that was not an issue. Porsche, in an effort to circumvent
patents by Girling and Dunlop, designed a peripherally supported disk
with an inside grasping caliper. This was soon dumped and work
continued with ATE-Dunlop.
>>> Forget about GC and other calculations that muddy the straight
>>> forward relationship between downward and upward forces on the
>>> dropout in question.
>> 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.
> You're muddying the waters unnecessarily. You need to know the
> orientation of the force compared to the dropout slot, and the
> difference between the distance from the axle to the braking surface
> and from the axle to the tire contact patch. The first will tell
> you whether the reaction force from braking will push the axle out
> of the dropout; the second will tell you how much the force driving
> the wheel will be multiplied. The smaller the brake disk, the
> higher the multiplication of force- so a wheel with a 6" disk will
> result in a stronger ejection force that an 8" disk (a 26" MTB wheel
> being actually about 24" in diameter, so the difference is 4:1 for a
> 6" disk and 3:1 for an 8" disk).
Dropout slot orientation is a secondary consideration, entirely
missing the first problem which is that the disk brake causes
reversing (up and down loads) on the axle. If you use a motorcycle
type clamped axle, as some BMX bicycles do, then the problem goes away
entirely.
> The only number you need to add is how much force is resulting from
> forward motion of the bike, and for that you only need velocity and
> mass, not the rest of the stuff you're claiming is necessary.
No you don't. You only need to know the parameters I gave. If the
wheel skids, you have the force.
>>> I think caliper position is an obvious main item for discussion.
>> If the caliper is forward of the axle it will not try to eject the
>> spindle, but it will obstruct cooling of the disc. If the caliper
>> is aft of the axle the cooling will improve, but it will try to
>> eject the spindle. If the cooling _is_ needed are the ejection
>> forces outweighed by the existing retention forces?
> The caliper is behind for fork leg to protect it from hitting rocks,
> bits of tree and undergrowth. The location has nothing to do with
> cooling.
That's an excuse. You don't need to believe these convenient excuses.
Jobst Brandt
Michael Halliwell
> Mike Causer writes:
>>>Forget about GC and other calculations that muddy the straight
>>>forward relationship between downward and upward forces on the
>>>dropout in question.
>
>
>>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. You'll note this
> requires no further information about rider position or other bicycle
> dimensions.
Actually, if you're going to investigate the forces that could be
responsible for a wheel ejection, you need the more detailed level of
information that was indicated: that's how you isolate a force that
could cause an ejection and see if it has sufficient force acting in the
proper direction to yield the result in question...at least that's how
we looked at resolving forces in all my engineering classes and in my
professional practice as an engineer.
Now, have there been a bunch of non-walmart related incidents that I
haven't seen posted on the bicycle usnet groups, or is this really
related to all the wallyworld incidents? From what I've seen and heard,
most incidents have been related to uninformed people getting less than
ideal components and no user information (i.e. manuals) from a large
chain store (causing user error) rather than the one-on-one information
and support that goes with quality components and a "real" bike shop
(possibly indicative of a design flaw).
Myself, I've been running disc brakes for a fair bit of time now and
have had absolutely no issues with QR's becoming loose, wheels becoming
misaligned or wheels dropping out of the forks.
>
> 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.
>
> Jobst Brandt
Actually, vented rotors can break up the boundry air flow along the
surface of the disc, causing an improvement in the turbulent airflow
near the disc surface and better air movement around the disc (and
better cooling as a result). They also allow any mud that may get
caught in the caliper area a chance to escape that isn't present in a
solid disc, improving the wear of the braking system. If you're in doubt
about the airflow, it is essentially the same reason that golfballs
aren't smooth.
Psycho Mike
James Annan
> 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.
James
Clive George
news:jack-C97CBA.2...@newsclstr02.news.prodigy.com...
>> > 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?
clive
Simon Brooke
jobst....@stanfordalumni.org ('jobst....@stanfordalumni.org')
wrote:
> Dropout slot orientation is a secondary consideration, entirely
> missing the first problem which is that the disk brake causes
> reversing (up and down loads) on the axle. If you use a motorcycle
> type clamped axle, as some BMX bicycles do, then the problem goes away
> entirely.
FWIW downhillers now usually use 'through axle' designs as well, as do
seom 'freeride' bikes. The Cannondale 'lefty' and USE 'SUB' monoblade
hubs are also immune to the ejection problem.
--
si...@jasmine.org.uk (Simon Brooke) http://www.jasmine.org.uk/~simon/
;; not so much a refugee from reality, more a bogus
;; asylum seeker
Mike Causer
> 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.
Mike
David Martin
Unless the point of contact is behind the caliper (eg the bike is
rolling off a rock) in which case the weight of the rider + bike will
add to the ejection force rather than reduce it.
Given that the few reports we have of incidents are from people
descending rocky terrain at speed, the simplistic testing that has been
done, doesn't appear to be particularly realistic.
..d
Mike Causer
> Yes but that was not an issue. Porsche, in an effort to circumvent
> patents by Girling and Dunlop, designed a peripherally supported disk with
> an inside grasping caliper. This was soon dumped and work continued with
> ATE-Dunlop.
IIRC some aircraft brakes use this layout. Possibly because they can get
the maximum disk diameter for overall package size. You and I were in
competition then, because I used to design brakes at Girling in the early
1970s.
Mike
Mike Causer
>> 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,
The worst case of caliper location is to have it on the horizontal axis
of the spindle, and the rejection force is going to be the Gee times the
rider+bike weight times the ratio of tyre diameter to effective disk
diameter. I do not have a disk-braked bike to measure up, so I'll take
Tim McNamara's assertion that a disk could be 6" or 8" -- although the
26" tyres I've just measured were 25" (slick) and 26" (knobbly) in
diameter. This gives a ratio of 4.3:1 using the worst case of smallest
disk and largest wheel.
So the rejection force is going to be:
0.65 * W * 4.3 = 2.8 * W
Opposing this we have 1.0 * W the full weight of rider + bicycle,
because at maximum retardation the back wheel is off the ground.
Therefore the spindle clamping forces actually need to handle 1.8 * W,
a reduction of over one third on the calculation that didn't take the
weight factor into account.
Mike
David Martin
Except that it is perfectly possible to set up a *stationary* bicycle
such that increases in rider weight will increase the ejection force.
ASCII art is difficult to represent this with so here is a set of rough
coordinates. We assume the rear tyre is locked. Makes no differnece
either way.
0,0 is the contact patch of rear tyre on ground. (10,3) is the front
hub. (9,4) is the brake.
The key thing now is the contact patch. If it is flat level ground then
the contact patch for the front tyre will be at about (10.1, 0) , ie in
front of the front hub. As long as the contact patch is in front of the
brake, the force from the rider will act through the brake mounting
against an ejection force. As soon as the contact patch moves behind
the brake, the riders weight adds to the ejection force.
So your simplistic calculation is only correct for a normal, stable
bicycle where the contact patch is as intended on a flat road. On rough
terrain the forces can be vastly different and that is before starting
to consider peak loading. To take this to the extreme, heading down a
rocky descent the front wheel becomes unweighted but the brakes are on
and binding the wheel. The wheel comes back in contact with the ground
but it is the back edge of the wheel which strikes first, providing a
peak load amplified by the riders weight which pivots around the brake.
The force able to be applied has a mechanical advantage of 3-4 times
(ratio of the distance of contact patch to pivot vs pivot to hub.
..d
Tony Raven
> 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.
--
Tony
"Man is a credulous animal, and must believe something; in the absence
of good grounds for belief, he will be satisfied with bad ones."
- Bertrand Russell
Mike Causer
> 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
David Damerell
>Life sucks and shit 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 <dame...@chiark.greenend.org.uk> Kill the tomato!
Today is Olethros, February - a weekend.
Werehatrack
>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.
David Martin
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
Jay Beattie
"James Annan" <still_th...@hotmail.com> wrote in message
news:1139194034.2...@z14g2000cwz.googlegroups.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.
Werehatrack
<still_th...@hotmail.com> wrote:
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.
Werehatrack
<dame...@chiark.greenend.org.uk> wrote:
>Quoting Andy H <Oohd...@notagain.com>:
>>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.
jobst....@stanfordalumni.org
>>> 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
Alex Rodriguez
jobst....@stanfordalumni.org 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
Mike Causer
> 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
Mike Causer
> 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.
If you open your copy of Bicycling Science 3rd Ed to page 244, you will
see that DGW shows the calculation of the maximum retardation possible for
any bicycle configuration and that it depends on the position of the
Centre of Mass. As the ejection force depends on the actual retardation,
it should be clear that the maximum ejection force generated is directly
dependent on the maximum retardation possible which is directly dependent
on the rider position.
(If you only have the 2nd Edition it's page 197.)
Mike
jobst....@stanfordalumni.org
>> 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.
> If you open your copy of Bicycling Science 3rd Ed to page 244, you
> will see that DGW shows the calculation of the maximum retardation
> possible for any bicycle configuration and that it depends on the
> position of the Centre of Mass. As the ejection force depends on
> the actual retardation, it should be clear that the maximum ejection
> force generated is directly dependent on the maximum retardation
> possible which is directly dependent on the rider position.
That is for retardation of the bicycle and rider. It has nothing to do
with what is essential to the force on the dropout.
Jobst Brandt
Mike Causer
>> If you open your copy of Bicycling Science 3rd Ed to page 244, you will
>> see that DGW shows the calculation of the maximum retardation possible
>> for any bicycle configuration and that it depends on the position of the
>> Centre of Mass. As the ejection force depends on the actual
>> retardation, it should be clear that the maximum ejection force
>> generated is directly dependent on the maximum retardation possible
>> which is directly dependent on the rider position.
>
> That is for retardation of the bicycle and rider. It has nothing to do
> with what is essential to the force on the dropout.
So are you saying that this ejection force exists even if there is no
braking? Or if it only exists under braking, that it does not vary with
the amount of braking effort?
Mike
James Annan
> 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
--
James Annan
see web pages for email
http://www.ne.jp/asahi/julesandjames/home/
http://julesandjames.blogspot.com/
James Annan
> 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.
I don't believe that Trek ever did any testing - they certainly never
published any results.
I do know that Cannondale did some utterly hopeless, most likely
deliberately fraudulent "tests" and would not reveal the details except
through a Freedom of Information request:
http://www.ne.jp/asahi/julesandjames/home/disk_and_quick_release/cannondale.html
James Annan
Why would they do any testing? There were no reported failures, right?
Just like in the case of disk brakes - except in this case there
actually are several reported cases, which have all been brushed off by
the manufacturers - except for the ones who paid off a plaintiff.
James
davewis...@gmail.com
>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.
The statement above by the Trek Man shows that Trek is aware of
a general problem with the usability of the current quick release
system, but the statement seems to me that the analysis was
done with the conclusion in mind.
I've seen several beginning bicyclists misuse a quick release and
showed them the correct method of fastening the wheel. So I think
that bicyclists should welcome a simplification of the current design.
I ride very rough, rocky terrain, up to 20 percent grade, on my
full-suspension mountain bike with disc brakes. Since I became
aware of James Annan's alarming posts I have checked my QR's
and once found the front much looser than I remembered. So there
might actually be something to the story. Time wil tell.
In the meantime, I continue to ride the bike, which is made by
Trek. In the case of a horrible accident involving the separation of
the
front wheel from the fork I'd be contributing to my demise with
my own negligence, unless of course my lawyer could show that
Trek had not exercised due diligence investigating the issue.
That may be part of the reason Cannondale spent the time and effort to
look
at the problem.
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...
jobst....@stanfordalumni.org
I think the situation has been stated in plain English. If the wheel
stops, regardless of how heavy the rider and bicycle is, the force is
related as stated. It is dependent only on the load on the axle. You
don't need to know anything about the handlebar height, the seat
position or the weight of the rider. That is all contained in the
axle load and that the wheel is stopped from rotating by the brake.
That could be a skid or the beginning of an end-over.
The separation force is the wheel to disk diameter ratio times the
axle load in a direction tangent to the disk at the caliper.
Axle load is a downward force while the caliper force acts upward if
it is behind the axle. However, its force acts only on one end of the
axle in a direction tangent to the disk at the caliper. In addition a
horizontal skid force acts horizontally to the rear and is equal to
the axle load for events of interest. None of these parameters are
modified by other frame considerations.
Jobst Brandt
Michael Halliwell
You mean, like most manufacturers recommend before each ride in thier
owners manuals?
What a novel concept!
Psycho Mike
Tim McNamara
My Volvo splits the difference, with Girling at one end and ATE at the
other. Never have been sure why.
Tim McNamara
and eliminate the need for the discussion entirely.
Michael Press
<43e724c7$0$6992$ed26...@ptn-nntp-reader02.plus.net>,
"Clive George" <cl...@xxxx-x.fsnet.co.uk> wrote:
> "Michael Press" <ja...@abc.net> wrote in message
> news:jack-C97CBA.2...@newsclstr02.news.prodigy.com...
>
> >> > 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
Michael Press
<pan.2006.02.06....@firstnamelastname.com.inva
lid>,
Mike Causer <mi...@firstnamelastname.com.invalid> 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
Michael Press
Tony Raven <ju...@raven-family.com> 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
jobst....@stanfordalumni.org
>> 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
Michael Press
Werehatrack <rau...@earthWEEDSlink.net> wrote:
You have not commented upon the free body diagram.
--
Michael Press
Benjamin Lewis
> 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
jim beam
> 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.
jim beam
vibration.
jim beam
> 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.
jim beam
heretic.
jim beam
> On 06 Feb 2006 15:22:28 +0000 (GMT), David Damerell
> <dame...@chiark.greenend.org.uk> wrote:
>
>
>>Quoting Andy H <Oohd...@notagain.com>:
>>
>>>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.
indeed.
jim beam
so james, are you able to differentiate between someone that doesn't
operate their qr correctly [user error] and design flaw? no? are you
going to keep on ignoring the FACT that correctly fastened qr's retain
wheels with a significant safety margin? [also ignoring the efficacy of
lawyer lips of course.] until you can, you're simply the lunatic the
industry is going to ignore.
jobst....@stanfordalumni.org
>>>> 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?
Use your imagination. The rider is descending a bumpy trail, causing
intermittent lift-off. When he lands, the wheel skids and he bounces
again. Anyone who has some trail experience has heard and seen this
effect. It does not involve and end-over.
> (I don't know if you can, or by how much, but the point seems to
> have been neglected).
If you stop averaging for the bicycle, you'll see that fairly high
forces are absorbed. This is just like the people who cannot
visualize that a spoked wheel regularly gets peak loads that are as
much as four time the average load. That's why crummy wheels need
spoke prep.
Jobst Brandt
jim beam
> Benjamin Lewis 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.
>
>
>>You don't think you can momentarily spike the braking force above
>>that without doing an endo?
>
>
> Use your imagination. The rider is descending a bumpy trail, causing
> intermittent lift-off. When he lands, the wheel skids and he bounces
> again. Anyone who has some trail experience has heard and seen this
> effect. It does not involve and end-over.
so jobst, on my ride this sunday, i descended three sections of rocky
trail that were so steep, even hard braking at the skid threshold could
not prevent rapid acceleration. these were hard rock bumpy rock, no
loose surface to reduce tire friction. now, given that my qr was
exactly as tight after this ride as it was before, with not even
slippage evident, can you please explain to me how exactly ejection
force is spiking beyond retention force "descending a bumpy trail"? how
about the fact that i've never experienced slippage or ejection in the 3
years i've ridden disk brakes? you can answer from your own extensive
experience actually riding disk braked mountain bikes, right?
>
>
>>(I don't know if you can, or by how much, but the point seems to
>>have been neglected).
>
>
> If you stop averaging for the bicycle, you'll see that fairly high
> forces are absorbed. This is just like the people who cannot
> visualize that a spoked wheel regularly gets peak loads that are as
> much as four time the average load. That's why crummy wheels need
> spoke prep.
red herring.
>
> Jobst Brandt
G.T.
Get back to us when you descend something for more than 30 seconds.
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
James Annan
> until you can, you're simply the lunatic the
> industry is going to ignore.
It's not me they have to worry about, it's the injured riders seeking
compensation. But if they are happy to pay anyone off who gets as far
as serving a writ, this could go on a long time. Especially since the
journalists have apparently decided that their readers don't need to
hear about it.
James
Luns Tee
Two questions.
1) What is the distance between the brake disc and the caliper mount
2) How thick is the caliper mount on an MTB fork?
Then, from the answers, answer these questions:
1) What turning moment does the force of braking generate as
it's transmitted across this distance
2) What forces must be present in the caliper mount to support
this moment
-Luns
Clive George
> In article
> <43e724c7$0$6992$ed26...@ptn-nntp-reader02.plus.net>,
> "Clive George" <cl...@xxxx-x.fsnet.co.uk> wrote:
>
>> "Michael Press" <ja...@abc.net> wrote in message
>> news:jack-C97CBA.2...@newsclstr02.news.prodigy.com...
>>
>> >> > 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.
You might want to read what Helen wrote a little more carefully then, rather
than just leaping in in the manner in which you did.
> Being able to comment upon it in a useful manner is a
> prerequisite to productively entering this discussion.
Bollocks. Maybe the physics is all you're interested in, but there are other
ramifications - eg user interface, legal, and the one which Helen raised,
which is the perception of the problem.
cheers,
clive
Tony Raven
>
> I've seen several beginning bicyclists misuse a quick release and
> showed them the correct method of fastening the wheel. So I think
> that bicyclists should welcome a simplification of the current design.
>
Not just beginners. I put the following page up two years ago
http://www.cycling.raven-family.com/Dropouts/QR.htm
--
Tony
"The best way I know of to win an argument is to start by being in the
right."
- Lord Hailsham