Roll centers

[Will Owen <nashwill@domain.elided>]

Steve Moresi said (#238):

"The closer the roll center is to the CG the less roll
you will have, because of the smaller moment
generated.  What is really interesting is to get the
roll center
above the CG, and the car will lean _into_ the turn!"

Well, it gets more interesting than that - more
interesting, in fact, than anyone would want! What you
wind up with is all your weight transfer going lateral
instead of down. In addition, the "seat-of-the-pants"
information that most of us depend on, which requires
a certain amount of roll, is completely lacking. There
are several older cars that were notorious for this,
the most common being the Austin-Healys, which were
really tricky on wet pavement and almost undriveable
on ice, owing to a combination of low CG, high roll
center (leaf-sprung solid rear axle) and stiff
springs. My old Daimler SP250 could be fairly
terrifying in that respect as well. 

Roll center isn't everything, of course; simple swing
axles, such as were used on VWs and early Porsches,
have a roll center well above the axle centerline, but
the articulation of the half-axles and the reduced
unsprung weight helped grip, though at the expense of
other odd behavior...

Will Owen
(nurturing his own low roll center in
Pasadena, CA)
Yahoo! GeoCities - quick and easy web site hosting, just $8.95/month.
http://geocities.yahoo.com/ps/info1

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