Optimal pressure depends on you car's overall weight: The weight
of your car plus all contents and also the occupants
(yourself).
From there you should be able to calculate the optimal pressure
based on the contact patch you require from the tyres by equating
the weight of the car to the pressure exerted on each of the
tyres.
Different cars got different pressure req. Also, if you are racing,
you will also need to cater for pressure variation due to heat.
Unless you use naturally heat retardl inert gas (from a reliable
source), you have to cater pressure for this variation.
