2006 Pontiac Grand Prix Tire size and ramifications

Ok factory tire size is as such. Front tires are P255/45R18's and the rear are P225/50R18's. So the wider tires are on the rear therefore the wider rims would be on the rear too. This is what the factory set up would be according to GM. Now as far as buying new to change it now I wouldn't as long as the tires are the same height there is no problems with letting be at this time. Hope this helps

Thanks for your answer racefan966. Actually the wider tires ARE the tires is supposed to be on the front. This is how GM makes up for haveing a front wheel drive car with 303 HP. That being said my concern is more from that stand point. Could the impropper tire size somehow negativly effect the tire wear and other systems,(brakes,suspension).

Well interesting that isn't what my friend that works for GM told me, but anyway none the less no it will not cause problems as long as they are the same height that is all that is important. If you look at the tire stagger the tire height is the same. If it was my car I would either have the wider on the rear or the same width all around as it would look better that way. If it were me I would have 8" wheels all around and the P225/50R18's on too.

Your "friend" at GM may need to bone up on the model before giving you that kind of information. True both models are 18 high and it does make sense when you work thru the logic but the fact that they thought to specifiaclly make the sizes different because of the huge amount of torque coming from the front of the car still kind of hangs out in the back of my head. Of course if you go to the fanatics on the various GXP forums they claim that the earth will open up and swallow the car whole if you use all the same sized tires on back and front so I guess the thing is to see what happens. Either nothing or I have to get my car towed from a firey underground grave. Guess we'll see, or at least I will.

With all my years in the business and the performance builds I have done it won't be a problems if all tires are at same height. The front are wider for a better bite wider patch on the ground. I have a Mustang and Ford is know for the front end being wider the the rear not in tire size actual wider track. I put rear spacers on to equal the stance and man what a difference in handling. So I guess what I am saying is width is not quite as important as the height. If height isn't the same that will mess with speed sensors and abs sensors. However as alway's do what you feel comfortable with. Get in touch with you local GM dealer and see what they say if you need more peace of mind.