87 gp tire size

At a height limit of about 26.5/27"" tall, 255 in back, and 235 in front will fit with the correct rim offset (like 8" with 4" BS back or 7" with 3.75" BS front) and no inner fender mods.

If you go wider/taller than this in front you will need to do work on the inner fender, if wider in back you'll likely need to roll the fender lip. If you go shorter, you can get away with slightly wider tires. Completely reshaping/reworking the inner fenders in front and stretching/rolling the fender lips in back, 275's all around should fit without rubbing, but it will take work. I'm running 255's all around right now and it is close to max and my inner fenders have been worked..

GP fenders "concave in" about an inch at the wheel opening (compared to other G-bodies) and this reduces the size of the tire you can run without rub.

pontiac dragger24 said:

which tire from this list would fit the best without rubbing or having to buy special rims?

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From that list only the first ones, 235/60R15 will fit in front without rubbing with un-modified inner fenders.

Up to 255/60's will fit in back without rubbing, but the wheel offset has to be right, unless the back of he car is jacked up and/or the fender lip is rolled.

Front: 235/60/15
Rear: 275/60/15 or 295/50/15; Rear wheels needs to have no more that 4.5" backspacing

pontiac dragger24 said:

I'm buying 255/60/15 and need to know which rims to buy that will let the tires in the wheel well without hitting ouster fender or frame

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An 8" or 9" wide wheel with 4.5" backspacing. Summit Racing and Jegs offer a wide variety of them.

15X8 with a 4" BS is probably the ideal size for a 255/60. A 4.5BS would allow you to fine tune the frame spacing with longer studs and spacers, but 4" should still keep the tire mostly off the fender lip.