[thstone]

The stock tire pressures help to create the understeer that Porsche desired (as san rensho explained). First, try making the pressures equal all around. If still too much understeer, then go in the opposite direction (high in the front, lower in the rear) and see if that helps to get rid of it.

Stephen Wilson was also correct in that you need to keep the pressures high enough to avoid rolling the tire over too far.