From: jbrandt@hpl.hp.com (Jobst Brandt)
Newsgroups: alt.mountain-bike,rec.bicycles.tech
Subject: Re: Build specs for stiff front wheel
Date: 8 Oct 2000 00:53:27 GMT

Mark McMaster writes:

>>> The skewer makes a LOT of difference in the "stiffness" of the
>>> front wheel.

>> I don't know if this is an attempt at humor but if not, could you
>> explain how a wheel skewer can affect wheel stiffness?  I find this
>> patently absurd.

> This is a reference to bicycles with telescopic fork legs.  The
> skewer does not affect the stiffness of the wheel itself, but does
> affect the stiffness with which the wheel is held to the fork legs,
> which in turn affects the rigidity with which the fork legs are
> connected to each other.  Independent fork leg compression/extension
> can cause the wheel to flop from side to side.  A stiffer connection
> between fork legs and axle can decrease independent fork leg
> movement.

Well that's a stretch of definition and one not implied or mentioned.
Just the same, any reasonable fork should have a bridge that takes
care of any mismatch for this reason and for braking.  Besides, to
rely on the skewer to force equal plunger travel is a foolhardy
premise, considering the bending moment and extension forces this can
cause over the width of a jam nut.  That's enough to break any skewer
if there is a noticeable difference in damping or spring force between
the two plungers.

Jobst Brandt      <jbrandt@hpl.hp.com>

From: Mark McMaster <MMcMstr@ix.netcom.com>
Newsgroups: alt.mountain-bike,rec.bicycles.tech
Subject: Re: Build specs for stiff front wheel
Date: Mon, 09 Oct 2000 23:56:14 -0400

Peter Cole wrote:
>
> "Jobst Brandt" <jbrandt@hpl.hp.com> wrote in message
> news:8rogi7$cv0$2@hplms2.hpl.hp.com...
> > Mark McMaster writes:
> >
> > > This is a reference to bicycles with telescopic fork legs.  The
> > > skewer does not affect the stiffness of the wheel itself, but does
> > > affect the stiffness with which the wheel is held to the fork legs,
> > > which in turn affects the rigidity with which the fork legs are
> > > connected to each other.  Independent fork leg compression/extension
> > > can cause the wheel to flop from side to side.  A stiffer connection
> > > between fork legs and axle can decrease independent fork leg
> > > movement.
> >
> > Well that's a stretch of definition and one not implied or mentioned.
> > Just the same, any reasonable fork should have a bridge that takes
> > care of any mismatch for this reason and for braking.  Besides, to
> > rely on the skewer to force equal plunger travel is a foolhardy
> > premise, considering the bending moment and extension forces this can
> > cause over the width of a jam nut.  That's enough to break any skewer
> > if there is a noticeable difference in damping or spring force between
> > the two plungers.

I agree that a reasonable telescopic suspension fork would
have a bridge stiff enough to prevent independent leg
motion, but as low weight is strong selling point for
bicycle equipment (especially suspension forks), many forks
have rather minimal bridges.  These forks don't rely on the
skewer force specifically, but stiffening up the axle/fork
connection does have a measurable effect on reducing
independent leg action.

> This is very common in suspension forks, many have damping cartridges in
> only one leg.

And some have only a damper in one leg and only a spring in
the other leg (however I can't vouch for the performance of
these forks).

Mark McMaster
MMcMstr@ix.netcom.com

From: mhickey@cynetfl.com (Mark Hickey)
Newsgroups: alt.mountain-bike,rec.bicycles.tech
Subject: Re: Build specs for stiff front wheel
Date: Tue, 10 Oct 2000 11:36:08 GMT

Mark McMaster <MMcMstr@ix.netcom.com> wrote:

>I agree that a reasonable telescopic suspension fork would
>have a bridge stiff enough to prevent independent leg
>motion, but as low weight is strong selling point for
>bicycle equipment (especially suspension forks), many forks
>have rather minimal bridges.  These forks don't rely on the
>skewer force specifically, but stiffening up the axle/fork
>connection does have a measurable effect on reducing
>independent leg action.

Still, remember that the bridge is primarily there to prevent
independent VERTICAL movement of the fork legs.  The solid interface
at the hub / dropout interface also help keep the legs from twisting
during steep climbs (about the only time it's an issue, since it
doesn't take much "twist" to eat up the ~1mm brake pad to rim distance
that are the norm with V-brakes.

>> This is very common in suspension forks, many have damping cartridges in
>> only one leg.
>
>And some have only a damper in one leg and only a spring in
>the other leg (however I can't vouch for the performance of
>these forks).

It would make sense that it could potentially produce brake rubbing,
particularly on rebound (woudn't take much deflection at the hub to
induce a 1mm rim deflection).

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

From: dblake@popper.ucsf.edu (Dave Blake)
Newsgroups: rec.bicycles.tech
Subject: Re: Build specs for stiff front wheel
Date: 10 Oct 2000 15:40:27 GMT

Bob Mitke <bikescience@aol.comnojunk> wrote:
> Mark Hickey wrote:
>
> >The solid interface
> >at the hub / dropout interface also help keep the legs from twisting
> >during steep climbs (about the only time it's an issue, since it
> >doesn't take much "twist" to eat up the ~1mm brake pad to rim distance
> >that are the norm with V-brakes.
>
> Please provide a _magnitude_ of the bending moment/asymmetrical
> loading to induce this twist...
>
> I think it is unlikely to be the main culprit in brake rub - yes it
> contributes, but it is not the main source...

All the proof is in the pudding.

A racer friend and I were investigating this in Helen GA. He
had a Bullseye front hub with track bolts. We removed the bolts,
and rode the bike with titanium QRs, steel QRs, and the track
bolts.

Brake rub during climbing could not be demonstrated with the
track bolts. The brakes would barely rub with the steel QR
fastened firmly, and the brake rub was quite noticeable with the
titanium QR. The fork was a dual slider Rock Shox 21.

Since it is fairly easy to tap a hollow front axle, I suggest
you try the experiment yourself. The results are quite convincing
in that the culprit in front brake rub with a dual slider fork
is quite often uneven leg movement, and a firmer axle bond at
the dropout makes the movement too small to affect riding.

Another good place to demonstrate the effect is turning slowly
over stutter bumps. That really makes the wheel flop until you
start using track bolts.

--
Dave Blake
dblake@phy.ucsf.edu

From: dblake@popper.ucsf.edu (Dave Blake)
Newsgroups: rec.bicycles.tech
Subject: Re: Build specs for stiff front wheel
Date: 11 Oct 2000 03:31:43 GMT

Bob Mitke <bikescience@aol.comnojunk> wrote:
> Dave Blake wrote:
>
> >Brake rub during climbing could not be demonstrated with the
> >track bolts. The brakes would barely rub with the steel QR
> >fastened firmly, and the brake rub was quite noticeable with the
> >titanium QR. The fork was a dual slider Rock Shox 21.
>
> Out of morbid curiosity, what was the clamping area of each
> of the QR's?
>
> Was that variable held constant in your test?




No. The steel and titanium QR were comparable. The track
bolts had substantially smaller contact areas.



--
Dave Blake
dblake@phy.ucsf.edu