web page on disk brakes and quick releases

[James Annan]

I've finally got around to (nearly) finishing something I started some time ago. Those who have
heard about Russ Pinder's recent crash may guess what prompted me to do so (those who haven't, see
singletrackworld.com). Anyway, here it is, comments and criticisms are welcome. I have one or two
more things to add but think I might as well get this rough draft up now warts and all.

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

James

(of course, if people want the text contents posted rather than just a URL, then I can do that too -
basically it covers what I have already posted here on this subject a few months ago)

 

[Tim Woodall]

On 19 Mar 2003 06:13:36 -0800, James Annan <[email protected]> wrote:
> I've finally got around to (nearly) finishing something I started some time ago. Those who have
> heard about Russ Pinder's recent crash may guess what prompted me to do so (those who haven't, see
> singletrackworld.com). Anyway, here it is, comments and criticisms are welcome. I have one or two
> more things to add but think I might as well get this rough draft up now warts and all.
>
> http://www.ne.jp/asahi/julesandjames/home/fork/
>
> James
>
> (of course, if people want the text contents posted rather than just a URL, then I can do that too
> - basically it covers what I have already posted here on this subject a few months ago)

Back to the home page - goes to:

file:/D:/james/asahisite/index.html

Should (probably) be /index.html

Regards,

Tim.

--
God said, "div D = rho, div B = 0, curl E = - @B/@t, curl H = J + @D/@t," and there was light.

http://tjw.hn.org/ http://www.locofungus.btinternet.co.uk/

 

[James Annan]

Tim Woodall <[email protected]> wrote in message
news:<[email protected]>...

> Back to the home page - goes to:
>
> file:/D:/james/asahisite/index.html
>
> Should (probably) be /index.html

Ficed, thanks for pointing it out (and Clive too). Weird how netscrape composer tries so hard to
bugger up links!

James

 

[Dave Kahn]

[email protected] (James Annan) wrote in message
news:<[email protected]>...
> Anyway, here it is, comments and criticisms are welcome. I have one or two more things to add but
> think I might as well get this rough draft up now warts and all.

Good work, James. I'm persuaded that there's a problem. I presume that in all these crashes you
believe were misdiagnosed as catastrophic fork failure the front wheel was out of the fork? If the
QR was opened as a result of the crash you might expect to find damage on the lever. OTOH if the
wheel was pulled out before the fork failed you might expect to find scoring in the left dropout.
Any evidence along these lines that you know of?

There is a little error in the following phrase:

"I suspect that brake judder and may have a role to play..."

Either you've left out another factor, or the word "and" shouldn't be there.

--
Dave...

 

[Rupert Smith]

Having recently purchased a new bike with hydraulic discs and a QR front hub I'm a little concerned
by all this! A couple of weeks after I bought the bike having just completed a very fast downhill
with some hard braking at the bottom, I noticed that the front wheel had become loose and was
essentially just being held in place by the lips at the ends of the forks. Ever since then I have
tried to do up the QR as tight as possible (not that it was ever particularly loose), and the
problem hasn't occurred again. I think I was quite lucky. I'm definitely persuaded that there is a
problem. So are you saying that this would be less of a problem if a conventional axle rather than
QR one were used? I can't see this making much difference, although changing the angle of the
dropouts obviously would.

Rupert

 

[Pete Jones]

On 19 Mar 2003 14:00:18 -0800, [email protected] (James Annan) blathered:

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

Interesting.

I've been dubious about using disks with the rear facing dropouts on my Klein frame - visions of
slamming on the anchors to find the rear wheel rotating up towards my ****. However, rear wheel
failure is less problematic than a sudden front wheel failure.

By this logic, mounting the disk caliper on the front of the fork leg, rather than the rear, would
eliminate the problem?

----
http://www.btinternet.com/~peteajones/

 

[Tony Raven]

"Pete Jones" <[email protected]> wrote in message
news:[email protected]...
>
> I've been dubious about using disks with the rear facing dropouts on my Klein frame - visions of
> slamming on the anchors to find the rear wheel rotating up towards my ****. However, rear wheel
> failure is less problematic than a sudden front wheel failure.
>

James' article skips quickly over the lawyers lips issue saying no more than they are not there for
that purpose (true) while not analysing the effect of the fact they are there. It would be pretty
difficult to get a done up QR past them even if the QR had no retaining force. I don't know for
certain but would assume Fox forks have the usual lawyers lips which would rule this out as a cause
in Russ's case unless he had filed them off. James' failed forks did not have them and they had a
rear facing front dropout to compound the problem. We discussed this some time ago and I remain to
be convinced that James' problem was as he describes and there is plenty of evidence we (including
Russ) have raised before to support an alternative failure mechanism. Incidentally Russ had Pace
forks, which don't have lawyers lips, for some time without those forks "failing". Its worth
exploring but my personal opinion is that this is probably not relevant to the accident or most
forks fitted with disc brakes.

Tony

 

[Pete Jones]

On Thu, 20 Mar 2003 13:05:59 -0000, "Tony Raven" <[email protected]> blathered:

>Incidentally Russ had Pace forks, which don't have lawyers lips, for some time without those forks
>"failing".

Actually, that was why I asked. Having heard of at least one person having had a set of Pace forks
fail, and having knocked mine out of alignment, I'm looking for any excuse I can find to take a
hacksaw to them.

I don't use them (2001 ProClass IIs) anymore, but I know from climbing/caving that old bits of
knackered kit lying about always creep back into use given time. I want to put myself beyond
temptation...

----
http://www.btinternet.com/~peteajones/

 

[James Annan]

[email protected] (Dave Kahn) wrote in message
news:<[email protected]>...
> [email protected] (James Annan) wrote in message
> news:<[email protected]>...
> > Anyway, here it is, comments and criticisms are welcome. I have one or two more things to add
> > but think I might as well get this rough draft up now warts and all.
>
> Good work, James. I'm persuaded that there's a problem. I presume that in all these crashes you
> believe were misdiagnosed as catastrophic fork failure the front wheel was out of the fork?

Yes.

> If the QR was opened as a result of the crash you might expect to find damage on the lever. OTOH
> if the wheel was pulled out before the fork failed you might expect to find scoring in the left
> dropout. Any evidence along these lines that you know of?

I'm not sure, but I suspect that any such scoring (you mean on the face of the dropout, right?)
would be hard to distinguish from the general wear and fretting that you tend to see on a fork end,
at least at a cursory glance - and most victims probably don't think to look, they know how to use a
QR and it's obvious that the fork snapped... It wasn't very obvious on my fork even though it was
freshly painted and I know for certain that the QR pulled out. Of course I'm not a forensic expert
and a proper examination might make it clear.

James

 

[James Annan]

"Rupert Smith" <[email protected]> wrote in message
news:<[email protected]>...

> So are you saying that this would be less of a problem if a conventional axle rather than QR
> one were used? I can't see this making much difference,

Well actually I was thinking about the bolt-through designs where there is a physical retension of
some sort. However AIUI a nutted axle can provide significantly more grip, many riders use them on
the rear of horizontal dropout frames for singlepeed use, where QRs may not hold. The fatter axle
enables a higher compressive force to be reached on the dropouts. I'm not sure that this will be
safe enough, though. The whole idea of having a friction fastening holding against a strong pull
just seems plain stupid to me.

James

 

[M-Gineering Imp]

Rupert Smith wrote:
>
> Having recently purchased a new bike with hydraulic discs and a QR front hub I'm a little
> concerned by all this! A couple of weeks after I bought the bike having just completed a very fast
> downhill with some hard braking at the bottom, I noticed that the front wheel had become loose and
> was essentially just being held in place by the lips at the ends of the forks. Ever since then I
> have tried to do up the QR as tight as possible (not that it was ever particularly loose), and the
> problem hasn't occurred again. I think I was quite lucky. I'm definitely persuaded that there is a
> problem. So are you saying that this would be less of a problem if a conventional axle rather than
> QR one were used? I can't see this making much difference, although changing the angle of the
> dropouts obviously would.
>
> Rupert

A QR is a rather long and slender rod and therefore fairly elastic. Clamping force will not increase
much even if the axle is levered out of the dropout. Compare this to a solid axle which is only
elongated over a single dropout width.
--
Marten

 

[James Annan]

"Tony Raven" <[email protected]> wrote in message
news:<[email protected]>...

>
> James' article skips quickly over the lawyers lips issue saying no more than they are not there
> for that purpose (true) while not analysing the effect of the fact they are there. It would be
> pretty difficult to get a done up QR past them even if the QR had no retaining force. I don't know
> for certain but would assume Fox forks have the usual lawyers lips which would rule this out as a
> cause in Russ's case unless he had filed them off. James' failed forks did not have them and they
> had a rear facing front dropout to compound the problem. We discussed this some time ago and I
> remain to be convinced that James' problem was as he describes and there is plenty of evidence we
> (including Russ) have raised before to support an alternative failure mechanism. Incidentally Russ
> had Pace forks, which don't have lawyers lips, for some time without those forks "failing". Its
> worth exploring but my personal opinion is that this is probably not relevant to the accident or
> most forks fitted with disc brakes.

yards ABOVE the rider, and he was a further 25 yards ABOVE the bike. Do you think Russ chucked the
bloody thing back up there after the crash? The 'catastrophic fork failure' is exactly what you
would expect from going ends first into the ground and speed, but it was not the cause of the crash.
Maybe the crash scene isn't incontrovertible proof, but surely even you can see it's a bloody great
smoking gun?

I'll be happy to eat my words if anyone can come up with a half-credible alternative scenario for
this crash, or the 3 other similar recent ones that I know of and consider to be directly caused by
front wheel loss. Remember that even in my case, when it happened in front of my eyes and the fork
ends had no retention lips and were pointing the wrong way, people were falling over themselves to
invent fanciful scenarios involving hitting a large obstacle (on a clear road in daylight), blowing
out the tyre and wedging the wheel. After all, we all know that quick releases simply don't fail....

Of course the lawyer lips have some effect, but they are highly variable in design, and may not mate
very well with different QR heads. There's no reason for them to do so, after all they are not
designed to withstand a pull, and the only standard governing their design is a rule of thumb about
their total height (enough that an unfastened QR will not drop out).

You claim above that 'there is plenty of evidence ... to support an alternative failure mechanism',
so now it's over to you to explain what this failure mechanism is, and what evidence you believe
there is in support of it.

James