From: jbrandt@hpl.hp.com (Jobst Brandt)
Newsgroups: rec.bicycles.tech
Subject: Re: clinchers on the track?
Date: 31 Mar 1998 16:20:13 GMT

Sheldon Brown writes:

>> However, I don't believe that the lateral cornering forces are
>> higher on the track than on the road.  Since track bikes used fixed
>> gears, they can not lean over further than the angle at which the
>> pedals scrape the ground - typically about 30-35 deg.  Road bikes
>> easily exceed this angle on a regular basis.

I concur with this for the reason that road bicycles corner as low as
45 degrees to the road while track bicycles are limited to far lesser
angles by the sweep of the pedal whose crank is constrained to turn
continuously.

However, even at 45 degrees, the center of pressure of the contact
patch still lies within the width of the rim and therefore does not
constitute a tire rolling force.  Tire roll occurs from under
inflation as anyone who has experienced and observed a slow leaking
tire in a curve.  When the tire deforms, the center of pressure falls
outside the width of the rim and can cause tire roll.  If the tire
subsequently bursts, observers often assume it was cased by lateral
forces, not low inflation.

> Actually, the greatest lateral forces for a track bike are not when
> cornering at speed, but when jockeying for position, riding
> ve..ee.ee..ery sl..oo..oo..ly on the steeply banked track.  I
> believe the 45 degree value is in the ball park.

On the track a fully inflated tire has the greatest propensity to roll
in the standing sprint in the event the front wheel lifts off ever so
slightly.  This usually occurs at the outset of the jump, especially
if it is made in a curve where the banking is steep.  An initial low
speed causes a large angle relative to the track surface that
facilitates liftoff toward the inside of the track.

A graphic example of this is shown in an Olympic poster I have seen at
Wheelsmith, in which a rider collapses a front wheel from such a
maneuver.  It shows the wheel bending under the side load as the wheel
again re-makes contact with the track.

> Track bikes have higher bottom brackets, shorter cranks and shorter
> pedals than road bikes, by and large, to allow them to cope with
> these extreme angles.

I think if you put a pedal down and lean the track bike, you'll see
that this is not the case.  I'm sure your bike shop has a track bike.

Jobst Brandt      <jbrandt@hpl.hp.com>