More on disk brakes and wheel ejection

Maki Tartamillo writes:

We don't need no steenkin further research, as they say. All that
is needed is to move the caliper ahead of the fork, nothing more.
In my estimation, this is the only reasonable solution that would
conclusively solve the problem.

Redesigning the QR so that it cannot unscrew is easier, cheaper, and
backwards compatible.

Could you outline how such a device would work and how it would
prevent the axle from moving up and down alternately with braking and
normal load, the mechanism by which QR's are unscrewed?

As long as the attachment is a "dropout", having braking forces trying
to pull the wheel downward is a threatening condition that makes a
reasonably cautious rider worry about how tight is tight enough. The
less skilled or forgetful riders could fare worse. With the caliper
ahead of the fork, all these concerns are removed.

Jobst Brandt

Palo Alto CA

Chris Zacho writes:

...Or simply rotating the dropout slots so that the axle slides out
forwards, perpendicular to the action of the DB.

I think you missed the test of unscrewing QR from the up and down
alternating load on the axle. This unscrews the QR as has been
tested. As long as brake reaction forces pull down on the axle and
riding loads push the axle up, The problem of loosening and failure
remain.

Jobst Brandt

Palo Alto CA

Rick Onanian writes:

I'm not sure what you are envisioning. You would then have to flex
the fork legs outward to fit the axle, and most forks are too stiff
to be flexed easily by that amount.

No, you'd just pull the skewer right out of the wheel.

When you propose that, I take it you are not capturing the axle in the
dropout, as is customary with a QR, but are expecting the QR to hold
the wheel alone. In that case, the skewer would need to be about 10mm
in diameter as axles are now. What sort of axle for mounting
bearings, do you have in mind? I see these various suggestions as
incomplete designs and not practical solutions.

This doesn't solve the problem anyway. There will be some play
when the axle is fit into its hole. It would still get pushed up
and down to the extent of that play by braking and bump forces.
The play wouldn't result in wheel ejection, but it still isn't good
design.

Well, I'm no engineer, but an engineer could probably come up with
something like my idea but better. Or, just make the dropout holes
the same size as the hole in the hub -- the hub doesn't have any
play up and down on the skewer.

If you are not an engineer then you probably should consider axles in
holes without clearance a press fit and after some use a loose fit.
Since I cannot visualize what you have in mind, I suspect your method
has not yet been thought out to practical completion.

Jobst Brandt

Palo Alto CA

James Annan writes:

wrote in message
...


We don't need no steenkin further research, as they say. All that
is needed is to move the caliper ahead of the fork, nothing more.
In my estimation, this is the only reasonable solution that would
conclusively solve the problem.

I cannot understand what all the hand wringing is about. Just do
it! This is fretting at its worst.

Whether or not the caliper is moved on the forks there's a lot of
expensive bikes out there that will not or cannot get retrofitted.

I'm sure you've mostly worked this out, but the reason why the
manufacturers appear to be acting like paralyzed bunnies in
headlights is that once their liability is established, they will be
faced with a massive recall problem and an indeterminate backlog of
compensation claims.

I don't think it is as bad as you describe. If manufacturers acted
now, modified their forks and recalled existing models, a solid
defense would be that the current design was general practice for all
bicycles and that no one found fault with it until a large user field
had established with a large variety of rider demands and operator
skills. This would demonstrate a good faith response to a belated
discovery that should be without major criticism. This would be
different, had there been some manufacturers who placed calipers ahead
of the fork and to whom one could point as proof of a known hazard.

What is done as retrofit is up to the industry. I see making a fail
safe "bandaid" that may not be graceful or stylish, but it could be
made safe at the expense of clean elegance. I even envisage a
retention means that would prevent the wheel from ejecting but without
trying to prevent loosening, so that essentially a "buzzer" noticeable
(looseness) would alert the rider to tighten the QR.

Jobst Brandt

Palo Alto CA

wrote in message ...


I don't think it is as bad as you describe. If manufacturers acted
now, modified their forks and recalled existing models, a solid
defense would be that the current design was general practice for all
bicycles and that no one found fault with it until a large user field
had established with a large variety of rider demands and operator
skills. This would demonstrate a good faith response to a belated
discovery that should be without major criticism.

Maybe, but I haven't heard of any forks being recalled with this
problem in the past 4 months, and in the meantime riders keep on
getting seriously hurt.

James

On Sat, 09 Aug 2003 07:00:40 GMT, wrote:
Redesigning the QR so that it cannot unscrew is easier, cheaper, and
backwards compatible.

Could you outline how such a device would work and how it would

I don't know how it works, but I saw skewers with a button
that must be pressed before they will screw/unscrew, in a
LBS the other day.

prevent the axle from moving up and down alternately with braking and
normal load, the mechanism by which QR's are unscrewed?

I suspect that preventing them from being unscrewed, along
with screwing them tight in the first place, would prevent
any issue; at least, that's the impression that I got from
this thread. It could be a wrong impression.

As long as the attachment is a "dropout", having braking forces trying
to pull the wheel downward is a threatening condition that makes a
reasonably cautious rider worry about how tight is tight enough. The
less skilled or forgetful riders could fare worse. With the caliper
ahead of the fork, all these concerns are removed.

I agree that changing the position of the caliper and/or
changing the design of the existing open dropout system
would eliminate the safety need for a skewer that won't
unscrew.

Jobst Brandt

Palo Alto CA
--
Rick Onanian

On Sat, 09 Aug 2003 07:13:13 GMT, wrote:
Rick Onanian writes:
No, you'd just pull the skewer right out of the wheel.

When you propose that, I take it you are not capturing the axle in the
dropout, as is customary with a QR, but are expecting the QR to hold
the wheel alone. In that case, the skewer would need to be about 10mm
in diameter as axles are now. What sort of axle for mounting
bearings, do you have in mind? I see these various suggestions as
incomplete designs and not practical solutions.
snip
Since I cannot visualize what you have in mind, I suspect your method
has not yet been thought out to practical completion.

Very much true; somebody else mentioned similar questions,
and indeed, I realized that I did not think out the idea
to practical completion. It may be possible to create a
system similar to what I proposed, but there are certainly
better ways around the issue (like moving the caliper).

That is why I made it clear that I'm no engineer. G

Jobst Brandt

Palo Alto CA
--
Rick Onanian

I'm going to have some fun at Interbike with this one. Fox, Manitou,
RockShox, watch out!

--
Robin Hubert

In article ,
Rick Onanian wrote:

On Sat, 09 Aug 2003 07:00:40 GMT, wrote:
Redesigning the QR so that it cannot unscrew is easier, cheaper, and
backwards compatible.

As long as the attachment is a "dropout", having braking forces trying
to pull the wheel downward is a threatening condition that makes a
reasonably cautious rider worry about how tight is tight enough. The
less skilled or forgetful riders could fare worse. With the caliper
ahead of the fork, all these concerns are removed.

I agree that changing the position of the caliper and/or
changing the design of the existing open dropout system
would eliminate the safety need for a skewer that won't
unscrew.

Marzocchi already makes a quickly-releasable through-axle design called
the QR20:

http://www.marzocchi.com/eng/spa/pro.../popfeatures/q
r20.htm

It does require a hub built for a 20 mm axle, though. It's not really
aimed at disc ejection, but rather at preventing axles from breaking
under the abuse of freeriding and dirt-jumping maniacs.

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

Rick Onanian writes:

I agree that changing the position of the caliper and/or changing
the design of the existing open dropout system would eliminate the
safety need for a skewer that won't unscrew.

This is a recurring theme that misses the point as I see it. A hand
installed wheel, one without a wrench tightened conical "lug nut" as
on automobile wheels, WILL move, either because it is not tight enough
to restrain all movement, or because it was inadvertently not
tightened sufficiently. As long as the disengaging force on the axle
remains, the problem remains with any manually tightened QR mechanism
that I can visualize. In this respect, I find suggestions for a
modified QR or dropout are wishful thinking.

As I said, moving the caliper ahead of the fork is an absolutely
effective solution while any modification of the dropout without it
can only appeal to riders who do not believe that the current
configuration is dangerous or that it is operator error of not
tightening the wheel sufficiently.

Jobst Brandt

Palo Alto CA