"Actually you are the first person to bring up this issue"

A few weeks ago, yet another rider who had just upgraded to disk brakes
found that he couldn't reliably keep his wheel stationary in the
dropouts under heavy braking. So far, so normal. Having found my web
page, he then did what it seems no mountain biker before him has
bothered to do, and asked the manufacturers for advice. In all, he spoke
to Answer (Manitou), Fox Racing, and also Avid and Chris King.

The clever ones will already have worked out where the subject line came
from. Yes, to a man (actually, 3 men and one woman), they all insisted
that he was the first person to have ever brought this up with them, and
no, they had no plans to do anything about it, because no-one else ever
had this problem. One of them (Avid) did say that it was obviously
dangerous and he should not ride the bike in that state, but had no
useful suggestion as to what he could do to make it safe.

So there you have it. At this rate, by the time next year's complaint
comes in, they will presumably have forgotten this first one. How
convenient for them. Those who thought that it wouldn't do to kick up a
fuss because the poor manufacturers were doing their best, may wish to
re-examine their approach. Or else studiously ignore this post in the
vain hope that the problem will go away.

James

...or come back to rim brakes ;-)

Infidel! Heretic! Hiccup!

Shaun aRe

Well I've not had a problem yet but I do make sure the standard Shimano
skewers are very tight.
Also I've noticed the "Lawyer Lips" on my new Rockshox seem particularly
generous, I don't know if that's just a fluke or deliberate to help address
the (alleged) problem.
--
Regards,
Pete

We use thru-axles and pinch bolts on a majority of our bikes. It solves the
problem on having to worry if the QR is tight enough or not.

- CA-G

Can-Am Girls Kick Ass!

Is there such a thing as too tight? Is there a danger of the skewer
being over-stressed and being more likely to fail?

--
a.m-b FAQ: http://www.j-harris.net/bike/ambfaq.htm

a.bmx FAQ: http://www.t-online.de/~jharris/bmx_faq.htm

With quick-release, if you have the skewers too tight, they can make the hub
bearings bind. Giant's bike manual suggested that the levers were too loose
if closing them didn't leave an imprint in my palm. Doing so meant the
wheels stopped rotating within about 3/4 revolution, compared to around 20
when loose.

Jon

---
Outgoing mail is certified Virus Free.
Checked by AVG anti-virus system (http://www.grisoft.com).
Version: 6.0.624 / Virus Database: 401 - Release Date: 15/03/2004

Have you contacted someone like Watchdog (UK consumer affairs program, for
the non-UK readers on the x-post) to see if they are interested. There has
been a reasonable amount of publicity /within the interested groups/, which
are, unfortunately, regarded as a weird minority by the public, but your
average Joe Punter who buys a supermarket y-frame full-sus brick won't have
read this, and poor though they may be, discs are starting to appear on
these - and the users may not know (how) to check that their QRs are tight.

E

QR skewers certainly tighten the bearings, although it's something that's
always bemused me somewhat; how do they make so much difference when the
cones are locked onto a pretty un-compressable axle? I suppose it's just
that very, very little movement of the cones on the axle is required to make
a difference. Anyway, it's a normal effect, and needs to be taken account of
when setting the cones. There should actually be a little play before the QR
skewer is fastened. Not doing skewers up tightly isn't a good idea, although
I think the imprint in the palm is a *bit* extreme!

Version: 6.0.634 / Virus Database: 406 - Release Date: 18/03/2004

That's only true if the hub bearings are misadjusted. With properly
adjusted quick-release hubs, there's slight looseness in the axle
bearings when the skewer is not connected, and when the skewer is
properly tightened, this slack is taken up without causing the bearings
to bind.

See: http://sheldonbrown.com/cones

Sheldon "Insert Nickname Here" Brown
+-------------------------------------------------+
| To stay young requires unceasing cultivation |
| of the ability to unlearn old falsehoods. |
| --Robert A. Heinlein |
+-------------------------------------------------+
Harris Cyclery, West Newton, Massachusetts
Phone 617-244-9772 FAX 617-244-1041
http://harriscyclery.com
Hard-to-find parts shipped Worldwide
http://captainbike.com http://sheldonbrown.com

Cones can be loosened to compensate for a tighter skewer. In other words,
readjust so there's more play in the hub before QR is done up, to cope
with the greater axle compression when it is closed.
I don't think it's an issue for cartridge bearings.

This is besides the point though. There's obviously a fundamental problem
with the type of setup in question. Doing up the QR a bit tighter hardly
seems like a satisfactory solution.

~PB

Is this a competition?

--
DISCLAIMER: My email box is private property.Email which
appears in my inbox is mine to do what I like with.
Anything which is sent to me (whether intended or not)
may, if I so desire, form a legal and binding contract.

Umm, if it is you lose.

Bill "as would I" S.

I have a front disc brake on my Van Dessel Super Fly. I've only had to
do really hard braking on one ocassion, and I did not notice that the wheel
shifted. I do keep my QR tight and after reading about this potential
problem I decided against my usual practice of removing the lawyer lips,
just in case.
--------------
Alex

Not if it is steel.
----------
Alex

I'm pretty sure some manufacturers are now starting to put the disc on
the RH side of the fork. It's certainly an accepted problem.

Or you can just turn the QR around so the lever is on the right side.

I might be dense, but I can't see how that would help. I *can* see that
putting the calipers in front of the fork would help, but the right hand
side? What am I missing?

--
Dave
dvt at psu dot edu

Well, skewers do break. It's rare for good quality steel skewers to break
but others do.

Greg

I keep hearing about this issue with greater frequency, but I've been
running discs for a few years now and it's only popped out once in that
time. It was my fault on that occasion, I realized afterwards that I hadn't
properly tightend the QR.

Now that it's been mentioned though, I have noticed the "Lawyer Lip" on my
Bomber. It's a few years old too but it definitely keeps the wheel on even
with the QR loosened.

Don't rely on the lawyer lips like you would have back with cantilevers.

Greg

putting it on the right side of the fork would also put it on the front
of the fork if you're using existing brakes.
--
david reuteler
reut...@visi.com

? what does that fix?
--
david reuteler
reut...@visi.com

It's actually 1 Yr and 3 days :-(

Been wondering whether to get involved but decided I'd would.
Comments in reply to other posts
Legal action still pending, really ought to get on with it before someone
else goes the same way.

For anyone wondering what I'm on about see the link below

Russ
www.russ-appeal.org.uk

The axle does compress. Doesn't take much to affect the bearings.

~PB

Not when you're braking really hard with discs it doesn't

That was a line I used in the past, and I'd never had a wheel come out,
thought I was safe, had even tried to convince James it wasn't a problem.
Then it did - at the worst possible moment, 25 plus mph - very steep rocky
downhill. QR must have loosened somehow, don't know how but if I hadn't done
it up properly it'd have come out in the three hours previously, I knew
something wasn't right so tried to slow down, braking hard just ripped the
front wheel out and I endoed big time. I'll never get the chance again, all
because some idiot bike designers never thought about a clearly obvious
problem with discs and caliper positioning ripping wheels out of dropouts,
had the caliper been on the other side of the fork leg braking would have
forced the QR into rather than out of the drop outs and I'd have at least
been able to lose a lot more speed before stacking but would likely have
been able to brake to a stop.

It's only a matter of time until some-one else injurs themselves big time
too.

Russ
www.russ-appeal.org.uk

Prevents the problem.

how?
--
david reuteler
reut...@visi.com

Chris King specifically warn against overtightening the skewer,
because compressing the (presumably cartridge) bearing will accelerate
wear and result in a wheel which is chronically wobbbly.

I don't know how tight a skewer would have to be to make it
significantly more likely to fail in itself, but I would imagine there
must be some tendency in that direction. Anyone who really cares could
always try asking the manufacturers themselves...but from what I've
seen, those who supply recommendations (eg lever torque) tend to give
both a lower and an upper limit.

James

Actually, it is the axle that is compressing, and Ti axles require less
force to compress as much as steel ones do.

Cones on a Ti axle should be even looser than those on a steel axle.

Dave

No, I don't think there is any point in that. Firstly, it doesn't
affect me directly, and secondly, they are hardly going to take a
complaint seriously that has only ever been noticed by one rider (and
he didn't even have a crash or anything, it's just that his wheel
won't stay put). Since it's already been cleared by the CPSC, there is
obviously no design problem and I guess I must have made the whole
thing up. It was quite a hassle making all the fake user accounts on
singletrackworld:

http://www.singletrackworld.com/forum/read.php?f=2&i=934406&t=933851

and just to make it seem more authentic I forged this review and
hacked into Marin's site:

http://www.marin.co.uk/marin-2004/reviews.php?ID=47

James

Assuming, of course, that there actually *is* a problem.

It'll be nice to see all that wonderful, properly-controlled data from
the laboratory testing.

When that comes out for public view, then we'll all be able to avoid
drawing conclusions from anecdotal evidence.
--
R. F. Jones

LOL. While I think you are an obsessed quasi-religious zealot, that's not
why I'm going to goof on you.....

Dumabass, Frobnitz was *supporting you* ! He was suggesting that rather
than spam up a bunch of newsgroups where people are probably smart enough to
tighten their QR, you should direct your efforts at the appropriate
regulatory agencies and actually try to do something to fix the "problem".
Your rejection of that course of action suggests that you're more interested
in pursuing your own personal crusade rather than actually solving a
problem -- percieved or otherwise.

Rather than thank him for the suggestion or offer a counterpoint to why it's
not a viable option, you launch into a paranoid rant asserting the veracity
of the claims while simultaneously asserting no direct interest. WTF???
Perhaps you should resolve the dispute between the voices in your head
before forcing us to sort through them.

Maybe you should bring that whole thing up with your doctor and he can check
you medication levels, eh?

Tom

> Jon

I heard Rimmer has a permanent imprint on his palm... oh yeah, that was
from squeezing his helmet too much ;-)
--
Slacker

2. leave the lawyer lips intact (don't file them off).

It's worked for me and my Hayes mech's.

- - - - - - - - - - - - - - - - - - - - -

"May you have the wind at your back.
And a really low gear for the hills!"

Chris Zacho ~ "Your Friendly Neighborhood Wheelman"

Chris'Z Corner
http://www.geocities.com/czcorner

> bearings bind. Giant's bike manual suggested that the levers were too loose

That indicates a hub bearing adjustment error

--
Andrew Muzi
www.yellowjersey.org
Open every day since 1 April, 1971

Good see you active on the ng's.

I think I disagree more than I agree about this issue, but regardless,
good luck and best wishes with the legal battle.
--
Slacker

Yeah, I realised that. I guess humo(u)r doesn't travel well.

Actually, although you probably mean well, both you and Frobnitz don't
seem to realise that I _did_ contact the "appropriate regulatory
authorities" last year. They (or, to be precise, the CPSC) said they
needed specific complaints of individual problems, rather than a general
warning of a theoretical design problem.

Of course, when I suggested that some of those riders who had described
their incidents might care to contact the CPSC, I was roundly criticised
for "scaremongering", and as far as I know, not a single rider bothered.
Many of those who understood the problem or had even seen it for
themselves had the touchingly naive belief that the manufacturers would
fix the problem all on their own and it would be overkill to actually
pressure them into doing so. Of course, what they didn't realise is that
the manufacturers have a strong financial incentive to keep the current
designs, since when Joe Bloggs upgrades to disks and finds his QR fork
is not up to the job, he then generally goes out and buys a bolt-through
fork. It's easy enough to see who wins out of this.

Roll on one year, and entirely predictably, the manufacturers are still
pretending the problem doesn't exist. They must be laughing all the way
to the bank.

As for J DeMarco at the CPSC, well he commissioned Mark LaPlant of
Cannondale to report on the issue, and surprisingly enough the turkey
didn't vote for Christmas. In fact he produced a bullshit whitewash
which he refuses to publish. But since all the manufacturers can
(apparently truthfully) claim that no rider has ever reported any
incident, there really is little more that the CPSC can (or probably
should) do.

I hope you will now agree that I have offered a counterpoint as to why
it is not a viable option, and I'm sorry for not giving sufficient
explanation earlier. The simple fact is that while MTBers refuse to do
more than grumble on bulletin boards, there is no real complaint to
raise with anyone. I realised several months ago that there was really
nothing more for me to do, but people still keep on emailing me with
their stories, and I thought this latest one was sufficiently
interesting to be worth sharing. Maybe next year there will be another.
Don't hold your breath.

James

See, that's the point. The brake should be designed so that it
*can't* force the wheel out of the dropouts, even if the QR is left
completely loose. It's a design flaw, an epic design flaw that will
cost some manufacturer a *lot* of money in court some day. No other
current brake design that I'm aware of puts an ejection force into
the wheel in normal operation, but front disk brakes do.

Not even remotely. You haven't been paying attention.

> Putting the caliper on the front of the fork would probably lead to
> it ripping off it's mounting.

How do you figure? The forces on the mounting bosses on the fork leg
would be the same as they are with the current design.

There's no doubt that there is a problem. The only question is how
often it happens.

Think of it like Microsoft Windows: *you* are the testing lab.

It would be nice to have something other than a detailed engineering
analysis quantifying the force and magnitude of the ejection force
created by front disk brakes mounted behind the shock fork leg, paired
with a detailed engineering analysis of how the QR can be unscrewed by
the repeated ejection force resulting from normal use. Ummm, oh yeah,
that's *not* anecdotal evidence. That's objective evidence, which the
anecdotes (including video of a front wheel ejection) serve to
support.

The fact that the brake creates an ejection force at all is evidence
of the design flaw. It's really quite simple. The arguments against
this citing improper use of a QR are just desperate smoke and mirror
attempts to obfuscate.

> BenS <u...@bensales.com> writes:

BenS is probably referring to the post type mounts (Manitou), where the
axes of the mounting bolts are parallel to the plane of the rotor. If a
caliper with this type of mount is placed in front of the fork, the
bolts are going to take the caliper braking load in tension (not a good
idea in general), whereas if the caliper is behind the fork, it is the
mounting posts that take up the load (and in compression), the bolts
serving merely to fix the caliper in place.

Of course all these don't matter to IS mounts, where the mounting bolts
lie perpendicular to the rotor plane.

You need to clarify that. Where is this video of a front wheel ejection
caused by the application of a disc brake? There has been the video of
a loose QR causing a wheel to come off the fork when the rider tried to
lift the handlebar while riding; you're not referring to that?

I'd have thought angling the drop-out so it faces forward would prevent the
axle rotating out if the pads are the pivot point.
I'm still trying to think of any negative implications from doing this as it
seems too easy.
Being cynical a non-mechanical implication would be manufacturers seen to be
fixing a problem they deny exists therefore admitting the potential problem
after the fact and leaving the industry wide open to litigation.
--
Regards,
Pete

Merkins. They just don't do irony, do they? Something to do with only
having senses of humor, not of humour. There's a lot goes missing with
that second 'u'.

Mind you, of course, most of them wouldn't recognise humour of any sort
if it fell on them in a thunderstorm.

Simon, generally phlegmatic, but occasionally sanguine.

PS Oh, and it was the _philosophers'_ stone.

--
si...@jasmine.org.uk (Simon Brooke) http://www.jasmine.org.uk/~simon/

;; Women are from Venus. Men are from Mars. Lusers are from Uranus.

Or you could fill your bathtub with brightly coloured machine tools,
whilst intoning in a cod French accent 'this is not a pipe'.

All things are possible.

But I don't see what it has to do with solving the brake ejection
problem.

Simon, rides a Lefty, doesn't have a problem.

;; MS Windows: A thirty-two bit extension ... to a sixteen bit
;; patch to an eight bit operating system originally coded for a
;; four bit microprocessor and sold by a two-bit company that
;; can't stand one bit of competition -- anonymous

As I've said previously, we ride a variety of singletrack and downhills
here, and the one time my QR let me down was traceable to my own fault.
After I tightened it up it didn't happen again the entire day. That was two
years ago and Blue Mountain. We had stopped off on the way back from
somewhere else and I happen to have the XC rig in the car. Everyone else was
riding FS freeride or DH bikes. I did the main ski run about 15 times that
afternoon...most of them "After" the QR came undone.

So the question is this: in each case where the problem occured, what were
the conditions? was it human error, or part failure?

>Richard Bates wrote:
>> On Fri, 19 Mar 2004 11:37:22 -0500, in
>> <405B21C2...@sheldonbrown.com>, Sheldon Brown
>> <capt...@sheldonbrown.com> wrote:
>>
>>> Sheldon "Insert Nickname Here" Brown
>>
>> Is this a competition?
>
>Umm, if it is you lose.

Don't pick "party doll"...

Mark Hickey
Habanero Cycles
http://www.habcycles.com
Home of the $695 ti frame

Changing the dropout angle or created enclosed dropouts like
motorcycles use would be one solution.

Their lawyers may have told them exactly that. A much better
strategy- from the lawyers' perspective of course- is to sit back and
wait for the injury lawsuits to happen. Since this design flaw has
been publicly discussed and acknowledged by well-known engineers and
by trade industry magazines, there is already grounds for litigation
to be considered.

Hmm. Thanks for clarifying this.

Which make sense.

No, James Annan has a video clip of a guy riding with some friends
across a parking lot; he hits the brake and the front wheel is
forcefully ejected and zooms away across the parking lot. He of
course stacks it headfirst into the pavement. Extremely dramatic and
demonstrative of the magnitude of the ejection force even at low
speeds.

Hey! We resemble that remark! (Hmm, that may be a too-American
cultural reference).

The good Mr Annan can claim his knee-jerk defensiveness was an attempt at
humor, but I don't buy it. Taken in the context of his other posts, I'm not
sure why one is supposed to view that through a humo(u)rous lense while
taking him seriously in all the others. Taken at face value, he's just
plain full of shit. He rejects the notion of contacting an agency who can
*do* something about the perceived problems, then retorts that he tried and
failed. Methinks he may want to recheck his facts or re-evalute the
veracity of his opinion. Looks like the laugh's on you.

Tom

Is it really so bad for the bolts to be in tension? As I understand this
stuff, the way a bolt works is that when you tighten it properly, you're
effectively loading it with a whole bunch of tension.

http://www.unified-eng.com/scitech/bolt/clamping.html

Now, it's even easier to hold together if you can get the parts to be in
compression, but it shouldn't be necessary for the forces a disc brake
is likely to exert on the bolts. A typical Grade 5 bolt has a tensile
strength of 120,000 psi. Now, the bolt cross sections are only a
fraction of a square inch, (my back-of-the envelope calculation is .02
sq. in.) but that still amounts to about 2000 pounds of tensile
strength, per bolt.

The spec in the quoted article above suggests taking the bolt to about
75% of yield in a typical torquing, so that means you've added maybe
1500 pounds of preload, and that means in order to rip two
well-tightened bolts off of the front of a brake caliper, you'd have to
generate some pretty scary braking forces.

Well, it doesn't matter, but now you're loading the bolts in shear,
something against which they are not well preloaded and not designed to
resist. Look around you in the world: how many examples do you see of
shear-loaded fasteners? The only examples besides disc brake mounts that
I can think of are riveted sheet metal in stressed-skin systems (as on
airplane skins), and they use a _lot_ of rivets. Wheel mounts do a
similar thing, but use conical nuts to prevent true shear loading.
Pedals are a bad example of how not to do this; read Jobst's entry in
the rb FAQ for why not.

Motorcycles are rapidly moving away from IS-style mounts to post mounts,
which they call "radial" mounting, as in radial relative to the wheel.
The claimed advantages are strength and weight.

--
Ryan Cousineau, rcou...@sfu.ca http://www.sfu.ca/~rcousine/wiredcola/
President, Fabrizio Mazzoleni Fan Club

Perhaps you should give it up for something you're better at...

I don't mean well at all. I responded 'cause I find humor in pointing out
logical inconsistency. I didn't "realise" you'd contact anyone because you
rejected the notion as not worthwhile. I'm pretty intelligent, but not
clairvoyent. I could have realized it had you bothered to mention it.
Maybe you should listen to the CPSC and ask why riders *haven't* contacted
said agency? Maybe your perception of the problem doesn't translate into
reality.

Conspiricy theory itself is always touchingly naive. If the manufacturers
change the design then you're vindicated and if they don't, then they're
involved in the cover-up --and you're vindicated again! Is that how it
works in the land of absolute truth? (...and that's meant to be ironic
humor for your challenged countryman, Simon). Don't understand? Perhaps
you'd better start here: http://tinyurl.com/282zg

....Or secure in the knowledge that the problem doesn't actually exist.

Again, not the "truth" you espouse so therefore it's a "whitewash". Next
you're going to tell us the CIA is behind it all right? Ya know, if you
could document actual circumstances (rather than internet anecdotes and
gossip), than you could prove the point to the apparently intransigent CPSC.

So we can look forward to a year's peace on the matter? Or does this mean
that anytime someone reports a UFO, ....er disk/QR malfunction we'll be
treated to another lecture on the apathy of the injured and the evil intent
of the bike industry? You complain of apathy on the part of MTBers who do
nothing but "grumble on bulletin boards", and then resign yourself to do the
same. Again -- is this more of the internal debate going between the
personalities who live in your head? Maybe you nailed it by suggesting
"there is no complaint to raise with anyone."

Just a thought

Tom

This is right, but torquing a bolt for holding parts together is
different from getting that bolt's threads to take a load above its
torque specification because it's not always just the bolt you worry
about, but what it's threaded into. Depending on length of engaged
thread, it's possible to have the threaded contact area to be smaller
than the bolt's radial cross-sectional area which means that even though
the bolt itself can survive the tensile load, the threads on either the
bolt or the material it's screwed into might not. See below.

You need to look at the mounting post threads strength, not the bolts
themselves. The posts are made of aluminium and don't have the
characteristics you outlined above. The post will strip first before
the bolt . Using _threads_ on bolts to take up loads is always bad
design; using the bolt body to take up tensile loads is _always_ better.

Go into a construction site and be awash with examples. Look at the
steel girders, beams and other metal support structures that are bolted
together. Look at the bolted structures on bridges; the parts that put
bolts in pure tensile loading don't rely on the _threads_ to take up the
load, but on the strength of the bolts themselves.

Bicycle wheel axles are bolts in shear. Imagine a design that relies on
your QR skewer directly taking up your weight in tensile loading.

Maybe, but you can bet money that the "new" radial designs will not be
relying on bolts' threads taking up the loads in tension.

That video has been clarified by Annan in http://tinyurl.com/2d3p3

********
"I should point out that this was not a wheel pulled out through
application of a disk brake. It was due to a stripped thread in the QR,
possibly due to overtightening, and then the wheel fell out. It's an
illustration of why 'just do up the QR tighter' isn't an answer, and
neither is 'so what, MTBers fall off all the time'. Even at low speed on
a level surface it isn't an everyday sort of fall.

http://www.ne.jp/asahi/julesandjames/home/ride.mpg"
********

It's not what you think it is.

What means "properly tightened"?

Hold it! Even though this has been discussed at great length here in
wreck.bike, it appears to me that most of the respondents did not
understand that a disc caliper behind the fork causes a wheel
disengaging force, and that repeated braking WILL loosen a QR.
Therefore, with the majority of contributors resting in the "James
Annan is all wrong" boat what you just posted gets us back to the
start, a few hundred responses ago.

Brake forces and their reactions are apparently to complex to be
discussed among bicyclists who believe anything bought in a bicycle
shop is safely designed.

http://www.ne.jp/asahi/julesandjames/home/disk_and_quick_release/

Jobst Brandt
jobst....@stanfordalumni.org

> So the question is this: in each case where the problem occured,

How about doing a test that takes about 30 seconds. Open the QR on a
disc brake equipped front wheel. Push the bicycle forward and notice
what the axle does.

Just so it is clear what occurs. The fork dropout rises from the axle
and is retained only by the retention lips. the motion involved will
cause a properly closed QR to loosen on repeated hard braking because
there is ever so little motion with each brake application. If the QR
is extremely tight, it can prevent this over a longer time but in the
long run, if the wheel is not removed for one reason or another and
reinstalled again made extra tight, it will loosen.

The point is that the wheel should not have disengaging forces while
braking. These would not occur if the caliper were mounted in front
of the fork.

Jobst Brandt
jobst....@stanfordalumni.org

I don't think that at all, but I'm also not going to condemn a product or
indict an entire industry as a result of some line drawings and vector
calculations. Apart from some internet anecdotes and urban legend, I've yet
to see anything remotely resembling evidence of a threat to the public
safety. To illustrate, my lovely wife subscribes to the CPSC mailing list.
We receive an email nearly ever day listing between 1 and 5 different
product recalls. These recalls typically describe what is often potential
flaws and possible dangers -- many of which are damn near laughable but
still result in a recall:

Here's a few examples:
http://tinyurl.com/223qd
http://tinyurl.com/2n2sn

Surf the site and ask yourself if the CPSC is going to overlook the disk
brake risk when bicycle product recalls are issued for injuries no more
severe than a broken finger. http://tinyurl.com/3yxvb

I'm the last person to believe the government (US or anywhere else) ought to
be the ever protective nanny, and I'm not suggesting that if the CPSC isn't
interested than there's no problem. I'm merely illustrating that the idea
of a huge conspiricy to cover up the problems, and a tremendous lack of hard
evidence suggests the "problem" exists in the realm of the theoretical only.

Hell, I don't even ride with disks and I think the whole debate is a crock.

Tom

It's not a conspiracy, it's a "we'll ignore this and hope it goes away".
It's not going to go away. I worked at a fork manufacturer who had two
major recalls. How long do you think it took them to admit there was a
problem? How long after that do you think it took the CPSC to get involved?
It wasn't overnight.

It's not a crock. There's much evidence that discs loosen QRs, and it's
obvious that the forces of the brake try to eject the front wheel. When I
tighten something, I expect it to stay tight. But I'll be checking my QRs
mid-ride these days, and someday I'll be buying a through-axle fork.

Greg

Dear Tim and Jose,

Is there some confusion here?

I think that Jose is referring to the video mentioned
below, which James Annan explained is just what Jose
described, a loose quick-release with no braking involved.

Here's the post from James Annan:

Adam Rush wrote:
>>In the meantime, watch the video Annan has of a front wheel being
>>ejected from a fork. It ain't gentle and it ain't pretty. Especially
>>for the guy riding the bike at the time.
>
>
> Do you have the URL?

http://www.ne.jp/asahi/julesandjames/home/ride.mpg

[end post from James Annan]

Is there a different video of a different crash in a
different parking lot that does involve braking?

Carl Fogel

What means "properly tightened"?

> See, that's the point. The brake should be designed so that it

Hold it! Even though this has been discussed at great length here in

Brake forces and their reactions are apparently too complex to be

http://www.ne.jp/asahi/julesandjames/home/disk_and_quick_release/

Jobst Brandt
jobst....@stanfordalumni.org

http://www.ne.jp/asahi/julesandjames/home/disk_and_quick_release/

Do you not believe that current disc brakes cause a disengaging force?
If not, why not? Did you try the test of pushing the bicycle forward
with an open QR and applying the disc brake? If so, did you not
notice that the fork lifts off the axle. You dismiss "line drawings
and vector calculations" although you are surrounded by machines that
are designed by these methods and find them reliable. The test I
offer does not rely on such derivative methods and gets directly to
the issue. How about trying that and apply your own analysis to it.

These both seem reasonable hazard warnings. The tire pump has a check
valve failure, something that has ejected pump handles to the ceiling
and the helmet doesn't meet specifications. What is "laughable" about
that.

http://tinyurl.com/3yxvb

I think you missed the explanations for this. I concur that without
someone reporting an injury from it, CPSC won't pick it up. The cause
for a wheel disengagement is not obvious and from what we read here,
even difficult to explain how a disc brake can cause a QR to loosen or
for that matter cause an axle to disengage from the fork.

You are making this a "huge conspiracy" as a straw man to discredit a
fact discovered that most people have not been perceptive enough to
recognize.

So why do you get so vehement about this issue that you call those who
understand it names and imply they are fabricating the effect?

Jobst Brandt
jobst....@stanfordalumni.org

I'm not sure that this occurrence is inevitable. The QR skewer doesn't
sit snugly inside the hollow axle; when the QR is tightened it doesn't
necessarily follow that the QR rod is resting against the axle.
Therefore, the axle can move along the dropout without the skewer
moving, especially if it's only ever so little motion. It follows then
that this annular gap between the QR skewer and the axle will require a
relatively larger axle movement to affect the skewer. Granted that the
skewer won't be always perfectly concentric with the inside of the axle
when QRs are done up, but the gap still exists and therefore tiny axle
motion doesn't necessarily mean QR motion as well.

True enough. However, I think QR loosening while braking needs to be
treated as a separate issue.

These are two separate issues which must be tackled separately. The
latter is obvious, can be easily shown by force analysis and simple test
that anyone can do, and requires no further proof. However, there
aren't "much evidence" that disc brakes loosen QRs. There are a lot of
anecdotes and theorising, but no solid proof.

Do that and log the number of times you find your front QR loose because
of disc braking. A reliable way of doing this is marking your QR knobs
against the fork with a marker after adequate tightening, and checking
regularly to see if these remain aligned.

James was using irony, and using it rather well. Eddie (Frobnitz)
"gets" irony, based on past exchanges.

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

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

In one case the welds are in tension, in the other, in compression. I
don't think it would make much odds, as I suspect the welds are more
than strong enough anyway, but I've been wrong before.

Changing the angle of the dropout would also work and probably cost
less.

Then try this simple test: take two bikes, one with rim rakes and one
with discs. Loosen the QR. Ride forward. Brake. See which wheel
jams.

In the case of the disc braked wheel the twisting of the axle due to
braking forces can actually cause it to jam at walking speed with the
QR loose, according to my admittedly unscientific test. And we all
know that QRs can - and do - pop open completely, on occasion.

A brake which tends to remove or jam the wheel on application, and
which is only controlled by constantly checking tightness of the QR,
is, in my view, inherently unsafe.

And yes, I do have a bike with front discs. I use allen-key QRs and
check them frequently.

I've included the entire text of your post, untroubled by intruding comments
because it is so funny I felt it should appear again. OK. You didn't get the
joke. That's fine. It's nothing (much) to be ashamed of. It does seem that
everyone else did however.

And frankly, the idea that because someone was serious in the past, prevents
them from being humourous now is preposterous. Can a stand-up comedian raise
a serious point? Could a mortician say something funny? (I believe it was
called "Six-feet Under", although I sadly missed it!)

Get out more. Get on your bike and burn off some of that bile.

"Have a nice day!"

Jon

Thanks for the clarification. I hadn't seen James's correction.

There has been some published evidence in trade magazines that this
does in fact happen. ISTR that the material has been quoted or
paraphrased at VeloVision (the trade magazine and Website not being
available to the general public). It's not overwhelingly great
evidence at this point, as I recall. But it's some data at least.

Just to point out, Jobst, that that's a misattribution. I didn't
write that. So I can't answer your question.

I wrote the above, though, and thus am responsible for any errors,
misconceptions or rank stupidity it may contain..

Umm, yes, I do understand that model in concept. Just didn't mention
it in this paragraph as I was focusing on the fundamental problem that
disc brakes create an ejection force in the first place, and not
commenting on the progressive unscrewing of the QR from repeated
application of that ejection force.

Hmm. Thought I was agreeing with Annan. Somehow it got construed
that I don't.

Try diagramming out the forces. You'll see that they work out to be
about the same whether the brake is in front of or behind the fork
leg.

What is the point of advising that? You would just call it another
"anecdote". It's already been done and QRs have been observed to rotate.
See
http://www.ne.jp/asahi/julesandjames/home/disk_and_quick_release/index.htm
l

~PB

If you had glanced at the website you would have seen. In fact, anyone
coming new to the debate who thinks they have some startling insight
should probably read it. My dealings with the CPSC are detailed at

http://www.ne.jp/asahi/julesandjames/home/disk_and_quick_release/cpsc.html

and you might learn something from the related pages too.

I suggest you read the letters I've posted on that page, and try to work
out a plausible explanation for his behaviour.

A quick summary:

I emailed DeMarco several times in August and September, and was
repeatedly told that a letter was on its way, or had even been sent.
Eventually I got a bland Word document as an email attachment.

In mid October, I received the official letter which was significantly
different. Although dated 2 Sept, it was only posted on the 15th
October, a couple of days _after_ the ASTM meeting to which it refers.

DeMarco has not replied to any of my emails since that date. Mark
Laplant refuses to publish his report which was presented at the "open"
ASTM meeting.

Ask them yourselves if you don't believe me. Oh, I forgot, you're one of
those who prefer to piss and moan on usenet than actually _do_ anything.

James

I still fail to see the veracity of the mechanism proposed for QR
loosening with disc brakes. If you look at one of your QR hubs, you'll
see that the QR skewer is loose within the hub axle. For an XT hub this
annular gap can be a maximum of about 1mm. When the axle is snug
against the dropout, and the QR is tightened, the skewer and the axle do
not form a directly connected unit. Very small movements of the axle
will not necessarily move the skewer itself because of this annular gap.
At the worst case, the axle will have to move radially by about 1mm to
touch the skewer, and move just a bit more than that to move the skewer
as well. The axle will then have to move back by more than a mm to push
the skewer back as well. In other words, the axle will have to have a
cyclic movement of over plus and minus 1mm amplitude in order to affect
the skewer, to which the QR knobs are connected. Cyclic movement by the
axle of this magnitude will be quite noticeable. It will also be quite
obvious if the axle moves so significantly when the inside surface of
the dropouts are examined. There hasn't been any mention of this that
I've seen anywhere. Hence I see a need for scientific testing of this
mechanism.

>
> Jobst Brandt
> jobst....@stanfordalumni.org

I done this test (by accident) before this whole issue ever surfaced.
Indeed, it does want to pull out, which only proves "our" point; An
improperly installed front wheel (disc + QR) is a very, very dangerous
thing.

So what's your point again?
--
Slacker - been DH'ing w/6" rotors on QR front wheel for the past 2 yrs

Says it all, really. If you did, you wouldn't.

Mind you, of course, a through axle solves all the problems, and a
monoblade pretty much has to have a through axle, so there's yet
another reason to go monoblade...

--
si...@jasmine.org.uk (Simon Brooke) http://www.jasmine.org.uk/~simon/

;; single speed mountain bikes: for people who cycle on flat mountains.

Show me exactly where someone has done what I stated, because I don't
see it. The "anecdotes" consist of people looking down to see their QR
already loose and rotating (there are many causes for this, who knows
what happened), or one guy who thinks his QR got loose because he opened
and closed them before and after some rides and he "felt" they were
looser. My suggestion is a lot less subjective and one of the easiest
things to do. It also lends itself to observation of a gradual
progression of loosening. Isn't it strange that these "anecdotes" seem
to consist only of observations on either end of the spectrum, that the
QR is tight at the beginning , and the QR is already loose or
open/turning. The method I suggest will show the stages in between, and
will confirm if it's the cyclic loading of the axle that is the cause.

Yes, I'm currently doing this on my QR and disc-equipped bike, and have
yet to see any movement of the QR knobs.

Obviously you don't get the point either, Jon. I caught the sarcasm in
Annan's post from the outset. My point was that it was utterly defensive
and misdirected in light of the suggestion to contact an advocacy group. I
concur, people can easily switch between serious discussion and humor.
However I don't often see someone zealously espousing a crusade and then
turn to self-effacing humor on the same topic. Smacks of schizophrenia to
me....

I'd love to go out and ride, but injury prevents that. Bile's all I've got
for the moment (<----sarcasm)

Tom

OK, how about addressing this issue now. Rather than saying it
doesn't happen from braking in face of explanations on how it can and
does occur. Let's hear what you imply you know about this and are
keeping secret.

Jobst Brandt
jobst....@stanfordalumni.org

We don't all need to go to the moon to agree with what scientists on
earth theorized before astronauts verified it. Consider that both
fork legs carry a vertical load and a horizontal load from braking.
In addition the leg with the disc brake caliper has a torque equal to
the total brake force times the radius of the wheel applied to its
end. This differential cases a differential twist of the fork
dropouts that can incrementally unscrew the QR. This effect together
with vertical motion of the brake side of the axle is the mechanism
that can unscrew a QR. In some cases this can make the thread tighten
and loosen, in others it can cause a loosening creep.

In any case, loosening QR's was not a problem before widespread disc
brake use. This sounds like cracked rims all over again.

Jobst Brandt
jobst....@stanfordalumni.org