On Mon, 8 Sep 2003 21:13:22 -0500, john_childs
wrote:

The downhill part of the trail had the additional challenge of a rut
running all the way down the trail.

I saw the rut (gully) only being mentioned once while the correlation
with downhill seemed to be stronger, through several downhill and
uphill (and even flat) datapoints.

However, I think jagur and Tony are right. It might have to do with
tyre pressure, combined with a narrow rim, more than tyre tread per
se. And it's worse for downhill.

I'm not sure I can adequately explain the effect in just words but
I'll give it a try. Suppose you ride at a place where there is some
sideways slope. This could be road camber, or a downhill or uphill
trail where you drift out of the centre of a rut. The tyre, as usual,
begins contacting the ground at the front of the contact patch and
that particular bit of tyre doesn't slip. But once that bit of tyre is
in the middle of the contact patch, the soft tyre and narrow rim allow
the wheel to sink down locally with respect to the tyre. This gives a
steering momentum that on an uphill tends to steer the uni to the
steepest gradient, while on a downhill it tends to steer the uni away
from the steepest gradient. Hence on an uphill the effect stabilises
the uni in a straight line, while on a downhill any deviation from the
straight line (which might be e.g. in the centre line of the gully) is
intensified.

Klaas Bil - Newsgroup Addict
--
If the crank is moving then it really sounds as if it's loose. - onewheeldave trying to pinpoint the cause of a clicking crank