Re: Roebling Road report/yet another question

[Simon Favre <simon@domain.elided>]

Bill Bain wrote:

>A Question:
>
>Since the scale was working, I put my '83 Spider on it for fun.  Here's
>the values in pounds (full tank of gas, all fluids, empty trunk, no
>spare):
>
>No driver:   Total 2469  Corner weights:  LF 697, RF 660, LR 554, RR 558
>Driver (me)  Total 2657  Corner weights:  LF 755, RF 677, LR 620, RR 605
>
>Question:  What do corner weights tell you?  Do disparities in corner
>weights indicate anything about the health of the suspension?  On my
>Spider, the LF corner weight is quite a bit higher than RF even without
>me in the car.  Intuitively, it seems that the goal should be to have
>the corner weights about equal left to right, otherwise the heavier side
>would have a larger contact patch and the handling would be imbalanced.
>It also seems that if you know that one side is heavier, you could
>adjust the tire pressure in an attempt to equalize the size of the
>contact patch.

What's more important is what's called the cross weights. Add the LF and
RR, then add the RF and LR weights. The diagonal sums are a better 
measure of how well the suspension is set up. For racing purposes, you
want the cross weights as close as possible WITH the driver in the car.
A normal street machine is generally supposed to be set up for a balanced
load. Why is this important? Ever sat at a table with one short leg? If
your corner weights are way off, it will generally cause one rear wheel
to lock up under hard braking.

In your case, we get the following sums:

No driver:
LF+RR=1255,
RF+LR=1214, giving 41 lbs difference in cross weights. Not too bad, but
perhaps more than ideal.

With driver:
LF+RR=1360,
RF+LR=1297, giving 63 lbs difference. For real racing, some adjustment
would be advisable. The easiest way to change it is by substituting a
different shim under the front spring. Your right front could use a
thicker shim, or take some out on the left. For a street car, it's more
trouble than it's worth, unless you suspect past crash damage. The spare
tire being out may have skewed the numbers as well.

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