Re: Changing the roll center of a suspension

[Gerry Lehmann <lehmann@domain.elided>]

Nizam opens discussion on the value of lowering the roll center of a
Watts Link rear suspension car.  I don't profess to have the specific
answer but I do know that the question of whether its a good thing or
not, hinges on the relationship between the roll center and the center
of gravity at that end of the car. It is my understanding that it is
good for the roll center to be low, and I see the logic in wondering if
lowering it is better.  If it is at ground level, then all of the sprung
weight at that end is transferred through the springs and bars as a
vertical load, (a good thing) However.."If the roll center coincides
with the center of gravity, then all the sprung weight that is
transferred, does so through the roll center to the wheel and part of
that becomes traction reducing lateral load (not a good thing). The
closer the roll center is to the center of gravity, the greater that
effect will be"  (quote from Don Alexander's "Performance Handling"
manual)

My only point would be that it is a complex issue and you need to first
calculate the CG to know if moving the roll center would help or hurt
the situation.  I also can not find my copy of Fred Puhn's "How to Make
Your Car Handle", but having read it over several times some years
back,  I know that there is specific discussion of roll centers and
Watts link suspensions in that book. I believe the rear roll center is
fixed at the pivot point of the Watts link,  just as it is at the center
point of a Panhard rod car.  Fred is of course a diehard Alfa guy and
there is much Alfa discussion in that book.  I'll have to dig a bit
harder. So.....what does Larry say on the subject....Inquiring minds
would like to know.

Gerry Lehmann
'86 GTV6 3.0

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