Re: Roll stiffness and cornering

[Audial@aol.com]

Andrew Duane asked how stiffening the front (or rear) swaybar affects
handling.
Remembering my misspent youth reading "How to Make Your Car Handle", 
the most important point to remember when balancing swaybars is:

The end of the car with the MOST roll stiffness will slide FIRST.

So, if you want to increase oversteer or decrease understeer, stiffen the
REAR roll stiffness, shocks, etc.  

This is why some of those hot VWs with massive rear swaybars become very easy
to spin when surfaces get slick and their hot Yokohama race tires lose
traction.  

You have to be very careful when you modify the roll stiffness of the car
because the effects can be quite drastic.  Adding a fat front swaybar to a
car with a relatively soft rear suspension may make the understeer very
pronounced.  It is this way because the end of the car with the most roll
stiffness takes more of the chassis load in a corner, up to the point that
the tires break loose and slide.

Interestingly, I remember reading somewhere that Lotus often sets its cars up
so that they have a fair amount of body roll at both ends, and instead
concentrate on getting the shock damping characteristics spot-on.  The
rationale behind this is that a little roll gives predictablity and feedback
to the handling and the most critical element in adhesion in the "real
world", where backroads are bumpy, is impact absorption, wheel control, and
good suspension geometry throughout the range of travel.  Body roll itself is
not inherently bad as long as the suspension is well designed, i.e., the
geometry changes resulting from the roll don't adversely affect the roll
centers eccentrically.  The Acura NSX has a suspension that allows it to be
comparitively soft in roll because of its well-thought-out design.
 Swing-axle rear suspensions suffer from the "jacking effect" as a direct
consequence of the change in the height of the rear roll center, which causes
the rear wheels to assume positive camber and act as a lever to tip the car
over.  So Ralph Nader did have a point, and I wouldn't want to have swing
axles on my Quattro.  

On my '68 Corvette, I had a chance to experiment with this because I upgraded
the suspension to Koni adjustable shocks and adjustable swaybars at both
ends.  It took a lot of experimenting to get the handling sorted out, and the
process wasn't helped much by the fact that the older 'Vettes have both very
high unsprung weight (wheels, spindles and suspension pieces are cast iron or
steel) which necessitates stiff shocks, and a rear suspension that
drastically increases negative camber in bump absorption and positive camber
in droop.  Luckily, I installed a front bump-steer kit from Guldstrand
Engineering and a special strut-rod mount from another company that minimized
the rear geometry changes and made the car handle much, much better while
allowing me to set the rollbars and shocks a little softer so the car didn't
punish me too much.  

Someone on the List did an analysis some time ago of the roll-center height
vs. suspension position on a 5K Quattro that should be required reading for
anyone who wants to change their ride height from stock.