2006 Pontiac Grand Prix Tire size and ramifications

THEF1CHICK

MEMBER
2006 PONTIAC GRAND PRIX
V8
2WD
AUTOMATIC
44,000 MILES

Hi, I just bought a 2006 Grand Prix GXP. According to specs it is supposed to have 18x8's on the front and 18x7's on the rear but what it has is 18x8's on all tired. My question is, what is the worst that can happen if I dont get the smaller tires for the back right away. They are all fairly new to begin with and I dont see any uneven wear. Of course money is tight right now so I'm not jumping at the chance to buy 2 new tires plus a rim to use as a spare since it doesn't come with one but that's a different thing all together.

. Your help is very appreciated:-)

5 Replies

RACEFAN966

MECHANIC
5,029 POSTS

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

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Thursday, August 20th, 2009 AT 11:32 AM

THEF1CHICK

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3 POSTS

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).

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Thursday, August 20th, 2009 AT 11:59 AM

RACEFAN966

MECHANIC
5,029 POSTS

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.

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Friday, August 21st, 2009 AT 10:48 AM

THEF1CHICK

MEMBER
3 POSTS

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.