Not having any dealings with the type of car involved all that I would say is use a pyrometer to find out whats happening, and then decrease the front tyre pressures a couple of pounds and increase the rears by the same amount a few times to get a feeling if its altering anything.
You can play around like this, but normally you will find that it will only make a marginal difference and you should be looking at a suspension change like spring rates/anti roll bars/ toe setting/shock absorber settings etc.
Is it a steady state oversteer or only in slow or fast corners ?
Welcome to the Forum Andrew
