Over on the E36 M3 board, everybody talks about inflating both front and rear tires to the same pressure to decrease understeer (standard on my '98 M3/2 is 30 front, 35 rear). The explanation I've heard is that higher pressure reduces sidewall flex and gives a larger effective footprint when cornering. Autocross info sheets say to increase tire pressure front and rear, and I would be very surprised to see autocross recommendations that decrease traction.