Interesting thing i just read;
Always under the impression here that when vehicles had a wider/larger combo (ie Corvettes, Vipers, other super cars) the wide tires were on the rear not front.
Here are the specs I read. GM's reasoning is that meatier front tires will reduce understeer.
The new Grand Prix also will have a 5.3L V8 FWD set-up.
Bridgestone RE050A
Front: 255/45ZR18
Rear: 225/50ZR18