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From: gvcormack@watdaisy.UUCP (Gordon V. Cormack)
Newsgroups: net.auto
Subject: Re: Stiff vs soft suspension myths
Message-ID: <7275@watdaisy.UUCP>
Date: Fri, 24-May-85 01:41:45 EDT
Article-I.D.: watdaisy.7275
Posted: Fri May 24 01:41:45 1985
Date-Received: Fri, 24-May-85 06:34:08 EDT
References: <191@twitch.UUCP> <194@twitch.UUCP>
Distribution: net
Organization: U of Waterloo, Ontario
Lines: 55

> The load on each tire is completely
> determined by the radius of the turn and the speed around it,
> not the junk connecting the tires.  
> -- 
> Guido Bertocci
> ...!ihnp4!houxm!twitch!guido

The jist of the original article was correct; that you cannot
alter "weight transfer" on cornering much with suspension stiffness.
However, this statement and the original article are misleading in
a couple of areas.

First, the relative front-to-rear roll stiffness (which certainly IS
affected by sway bars etc.) has a great effect on how much of the
total weight trasnfer is borne by the front vs. rear wheels.
The reason that racing cars sometimes lift the rear wheel is that,
because the front outside wheel is heavily loaded anyway the
rear is given a lot of roll stiffness to offload the front tire a bit.
Lifting the rear tire is a symptom of a bit too much roll stiffness
in the rear.

Second, it is not true that the center of mass of a car cannot go
up or down due to lateral force.  It depends on the suspension
geometry.  The simplest way to explain this is to consider the
swinging half-axle geometry.  If the hinge point is anywhere above
the ground, the centre of gravity LIFTS with weight transfer.
This is called JACKING.  If the hinge is below the ground
(obviously impossible, but there exists suspensions with equivalent
geometry) the CG will LOWER with weight transfer.  Most cars
exhibit some jacking; extreme cases were cars like the Corvair and
VW Beetle, both of which had swing-axles and were known to 
tuck-under from time to time.  Stiffer suspension limits jacking and
therefore reduces weight transfer.

Weight transfer also occurs on front-to-rear acceleration.
"Squat" on acceleration and "Dive" on braking result from the
suspension lowering the CG on acceleration.  Geometry changes can
result in anti-dive and anti-squat suspensions.

Finally, who said weight transfer had anything to do with increased
or decreased cornering power?  I do not understand the argument that
begins: assuming tires have a constant coefficient of friction...
Assuming that, the weight distribution makes absolutely no difference.
Of course, tires are not perfect frictional devices, and that is why
one tries to transfer roll stiffness to the lighter end of the car.
But there is no simple formula for what that does.

The real reason that one wants to limit body roll is to try to keep
the wheels perpendicular to the road (0 camber).  This can be done
in spite of body roll with perfect suspension geometry.  But, for
various reasons, few cars have perfect suspension geometry.  So any
limit on body roll will keep the wheels closer to the proper camber.
-- 
Gordon V. Cormack      CS Department, University of Waterloo
   gvcormack@watdaisy.uucp     gvcormack%watdaisy@waterloo.csnet