re: suspension tuning

[James Montebello <jamesm@domain.elided>]

On Tue, 19 Nov 2002, Joe Elliott wrote:
> It's hard to say what the effect on overal grip would be if you just
> stiffen the rear to make the car tend more towards oversteer.  I
> think you would end up with more grip because even though you're
> making the rear let go sooner (relative to the front), you're
> reducing body roll, which will allow you to use more of the available
> grip from your inside tires, hopefully more than offsetting the
> tendency for the rear end to break away sooner.  The reverse is true
> for removing the front bar--more roll, less overall grip.

I don't think this holds true for a DeDion suspension, or a live axle, for
that matter.  Unlike a strut-type suspension (or, to a slightly lesser
degree, a double A-arm suspension), body roll has relatively little
effect on camber with a DeDion/live axle, and it's the camber change
that affects grip where body roll is concerned.  The front, of course,
is another matter, but I don't think it's as simple as Joe is outlining.

The traditional view is that adding more bar will reduce grip at that end
of the car, but this has been shown to be false on some cars (many makes
of fwd VWs, for example), at least to a point.  The idea is that adding
bar increases lateral weight transfer, which overloads the outside tire.
However, grip is also dependent on vertical load, and increases up to
a point, then slowly decreases.  The idea is to get the weight transfer
to work up to the top of that curve, but not go past it.

Depending on what you have on the car now, you may have to add or remove
front bar to properly tune the balance.  Changing the rear bar will
also have an influence on what the front does.  Completely remove rear
roll stiffness and the body will roll enough that the inside front will
unload completely.

james montebello
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