this is a little bit of car and drivers review of the GXP: Pontiac Grand Prix GXP - Road Test - Auto Reviews - Car and Driver
Pontiac's solution to these two inherent front-drive directional control problems—understeer and torque steer—is unique. Instead of four tires of equal size, the GXP has a lot more rubber up front than at the rear: Bridgestone Potenza RE050As, 255/45-18 front, 225/50-18 rear.
"We wanted a car to run with BMWs," says program engineering manager Phil Minch. "But we were limited by the W-car architecture, in other words, by front-wheel drive.
"The rear end never lets go when you have the same size tires all around. So we put our computer guys on it, and they came back with a recommendation for a smaller rear tire, to give the car better balance."
