Re: Suspension settings

["C.M. Smith" <cmsmith@domain.elided>]

Does everyone currently debating the correct settings for shocks (dampers)
and sway bars ( roll bars) keep uppermost in their minds the importance of
the tires' contact patches?  Handling begins and ends with the tires.

Adjustment to roll bars has the same effect as adjustment to spring rates,
except for two wheel jounce rates. I.e. the stiffer roll bar or the stiffer
spring will have the same effect in roll, the stiffer roll bar will only
make a difference if you hit a speed bump i.e. a double wheel effect, or,
put another way, stiffer roll bars give better single wheel jounce rates
for gripping the road surface.

Generally, increasing the spring rate or the roll bar stiffness will put
more pressure on the outside tire at that end of the car. If the tire is
already doing its thing the car will step out at that end. If not, then
overall grip will go up. Sometimes, stiffening the effective spring rate
will cause the inside tire to lift off the ground with no adverse effect on
grip, because the inside tire is not adding anything as the outside tire
has enough grip to do the job. On fwd VW this is best done at the rear
because the inside front is needed for traction. On the BMW 3 series the
inside front lifting apparently gives best results. On F1 cars all four
tires are asked to do their bit, but the driver can adjust both left/right
roll stiffness and fore and aft suspension stiffness as the tires wear and
fuel load changes.

For GTV6/Milano i suspect the overlooked element in the debate is the
effect of camber changes on the front wheels. The rear has fixed camber of
zero degrees (unless the rear axle is bent!). The front wheels develop more
negative camber as the body rolls. More negative camber gives better grip,
up to a point, then it tapers off rapidly. So, a softer roll bar in front
will allow more negative camber to develop in cornering, improving the
balance of the chassis, until the negative camber hinders traction.
Conversely, if you stiffen the roll resistance you will initially induce
more understeer until the chassis gets pushed really hard, then the slower
rate of camber change will provide a progressive reduction in understeer
and ultimately lead to a better balance.

Road & Track has a very interesting article in the June 99 issue on this
very topic and I highly recommend it to all those out there puzzling over
their race settings. Mario Andretti drives the best handling street cars
available in NA. The Porsche awd 911 does best, followed closely by the
Ferrari 355 and the Acura NSX. Most interesting are the infrared photos of
the four tires of each car after Mario has thrashed them. Tire temps are
shown in colour revealing which tires are doing the work, which directly
correlates to the overall handling of the cars. Also, the g meter envelope
pictures are printed adding a fascinating dimension to the analysis.

I don't race but I do read. Colin Campbell's excellent books on sports car
design are highly recommended for anyone tweaking his race car, or street
car for that matter. The Alfa 164 has an amazing fwd chassis which I think
is unequalled in the NA market. Not much improvement is available without
serious compromises in ride quality ( I just say this to attract
controversy).

 The GTV6/Milano chassis on the other hand must have loads of potential for
development because it is a rear drive street car with a first rate basic
chassis. Why is anyone trying to replace the torsion bars with coil overs?
Torsion bars give the lowest available unsprung weight and are rare because
they are tricky to integrate into the body and even trickier to set up. But
a spring with zero unsprung weight should not be replaced IMHO unless you
are really fanatical and can't find anyone to do a proper job on stiffer
rate bars.
Michael Smith
Calgary, Alberta
Canada
91 Alfa 164L, White, original owner 

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