Re: stability - was weight oilheads-digest V1 #75

[Bruno Valeri <bvaleri@xxxxxxxxxxxx>]

- ----- Original Message ----- 
From: "Bill Kaszer" <kaszer@xxxxxxxxxx>
To: <oilheads@xxxxxxxxx>
Sent: Friday, January 23, 2004 11:40 AM
Subject: Re: oilheads-digest V1 #75


>Whoever said that 325lb. 180hp superbikes seem to have no
problem
> staying on the track at 185mph was exactly right. Chassis
geometry and
> set-up are what gives a particular machine its stability, or
lack of.

Since we're on the subject. . . gyroscopic forces are a big
factor in straight line stability. Gyro forces increase with
rotational speed. The faster you go, the more the wheels will
resist deflection. At 150mph, a bike wants to go straight, even
one with radical steering geometry.

This is why many young and unskilled riders feel overly competent
on powerful sportbikes. As they accelerate hard or hurtle down
the highway at 100 mph, the bike feels very stable. They feel in
control. They feel skilled. Truth is, a bike is stable by itself
at speed. Needs no skill on part of rider.

Where skill comes into play is during slow speed maneuvering
where gyro force is very low. This is where those same riders
feel very awkward.

Having said this, I suspect that weight does play some factor in
straight line stability when encountering a sudden violent gust
of crosswind. I suspect that if you a take 2 identical bikes but
of differing weights (so sail effects etc are identical), the
heavier one will be more resistant to a powerful side gust.

During my trip out west, I got blasted by a couple of strong
gusts, one of which felt like it lifted the bike to some degree
as I drifted across the lane in the pelting rain.
http://pages.infinit.net/mcrides/west02/west3-3.htm

Since the coefficient of grip depends on weight pressing down (as
one of its components) a bike that is suddenly lightened in a
crosswind will experience decreased grip. In certain conditions
(ie wet surface) this may be enough to allow a lateral drift. At
least that's what I understood of the incident. Keep in mind,
these were very violent winds, the worst I've ever experienced.

Bruno
Montreal, Canada
CBR 929
http://pages.infinit.net/mcrides

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