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

Jose Rizal writes:

G.T.:

There's much evidence that discs loosen QRs, and it's obvious that
the forces of the brake try to eject the front wheel.

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.

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.

writes:

Tim McNamara writes:

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.

What means "properly tightened"?

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

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.

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

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.

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.

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.

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

"Just zis Guy, you know?" writes:

On Sat, 20 Mar 2004 00:13:45 -0600, Tim McNamara
wrote in message
:

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.

In one case the welds are in tension, in the other, in compression.

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.

Jose Rizal wrote:
G.T.:

There's much evidence that discs loosen QRs, and it's
obvious that the forces of the brake try to eject the front wheel.

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.

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.

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.

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...ease/index.htm
l

~PB

tcmedara wrote:


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.

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...ease/cpsc.html

and you might learn something from the related pages too.

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 bull**** 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.


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.

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 **** and moan on usenet than actually _do_ anything.

James

Tim McNamara:

Jose Rizal writes:

G.T.:

There's much evidence that discs loosen QRs, and it's obvious that
the forces of the brake try to eject the front wheel.

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.

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.

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.

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.


Jobst Brandt



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

in message fx07c.17600$Cf3.3839@lakeread01, tcmedara
') wrote:

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

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...

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

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

Pete Biggs:

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.

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.

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...ease/index.htm
l

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.

Jon Senior wrote:

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

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