Originally Posted by lt1 97 formula

i run 17x11 rims in the back i had to grind my bumpstops off and they fit great.

Originally Posted by Injuneer

17x9.5" and 17x11" Wheels on a 4th Gen

NOTE: ONE OR TWO PHOTO LINKS ARE TEMPORARILY "DOWN". THEY WILL BE BACK SOON. IN THE MEANTIME, SEND ME AN EMAIL AND I WILL FORWARD THE PHOTOS.

A popular setup seems to be:

Front: 17x9.5” wheels with 275/40-17 tires
Rear: 17x11” wheels with 315/35-17 tire

To make this work, you need wheels with the correct offset. Offset is a measure of how far the centerline of the wheel is pushed in over the mounting hub. For example, a 50mm offset pushes the centerline of the wheel about 2” deeper in to the wheel well, than if it had “0” offset.

For the 4th Gens, recommended offsets are:

Front: 17x9.5” – use an offset in the range of 38mm – 56mm. Here are some examples of front wheels:

56mm offset:
http://www.injuneer.com/images/photos/Rr34Dr02.jpg
http://www.injuneer.com/images/photos/Frt34vwD.jpg
(17x9.5 front only - rears are 17x11 50mm w/ 315/35)

(more photo links to be added)

49mm offset
http://www.injuneer.com/images/photos/210Full02a.jpg
http://www.injuneer.com/images/photo...s/21034_03.jpg
(17x9.5 front and rear)

45mm offset:
http://www.kellydrown.com/Showcase/120-2036_crw_std.jpg
(17x9.5 front only - rears are 17x11 45mm w/ 315/35)

38mm offset:
http://www.netsnapshot.com/users/439...rM_4394_41.jpg
(Right click, "Properties", copy and paste the link. Won't work otherwise).

If you run greater than 56mm offset, you run the risk of the inner edge of the wheel contacting the steering knuckle. If you use anything smaller than 38mm offset, the tire is going to stick out from under the front fender.

17x11" – use an offset of 50mm. If you go any larger on the offset, the inner edge of the tire will be hard into the inner fender liner. Any less offset, and the tires will start to stick outside the fender line, when you look straight down from above. 45mm is about as low as you can go and keep them under the fenders.

At least one popular wheel retailer, AFS, indicates that a 38.5mm offset is better for Trans Ams, while all other 4th Gens need the 50mm offset. I have never found any evidence to support the use of 38.5mm offset wheels on the back of a 4th Gen, and all the pictures I have ever seen show the tires outside the fenders.

AFS also indicates the 17" wheels can not be used on 4th Gen convertibles. This is not correct. While GM never put the 17" WS6 or SS wheels on the convertibles, many people have put them on, with no problems at all. I was persoanlly involved with putting the 17" ZR1/Grand Sport offset wheels on a 97 30th SS convertible, and it had the exact same wheel wells as my 94 Formula coupe.

50mm offset: (see also 56mm, above):


45mm offset: (see also 45mm, above):


For the 17x11 wheels, you MAY need to do one or more of the following:

1. Cut the outer, projecting edge off the jounce bumper bracket. With the car at normal ride height, the edge of the bracket will be slightly inside the opening in the rear of the wheel. When you try and jack the car by the body, as the wheel drops relative to the chassis, the bracket will catch on the inside edge of the rim and gouge it.



Some people do not cut the brackets - that seems risky to me. Others completely remove the jounce bumpers. That is risky as well. The jounce bumpers keep the chassis from slamming down on the rear axle assembly. They also protect the shock absorbers from excessive compression, which can damage them.

2. Hammer the inner fender liners. The tire may hit at the front of the wheel well. You take a 3# hammer and bash in the area where it rubs. Make sure your back seat is in the upright and locked position. If not, hammering on the wheel well could move the pin for the seat back and make it diffcult to latch the seat.



3. Recenter the body over the rear axle with an adjustable panhard rod. If the clearance between the tire and the inside edges of the tire and the inner fender liner are not equal on both sides of the car, you may need to adjust the side-to-side centering.

4. Roll the fender lip. At the edge of the wheel opening, there is a 1-2-3/4" wide horizontal "lip" that sticks straight out toward the edge of the tire. If you use an offset less than 45mm, if your body is not correctly centered over the axle, or maybe if you have soft panhard rod bushings, its possible for the lip to hit the sidewall of the tire on hard cornering, or even on a really heavy shift. To prevent this, the lip may need to be "rolled" up to it doesn't point at the tire.

Several ways to do this, including rolling a baseball bat between the tire and the fender, lightly hammering the lip, using a tool like "The Jimmy" that graps the lip and bends it upward at a 45-degree angel, or using a fender lip rolling tool like the one that The Eastwood Company sells (about $300). It is likely that the paint on the lip will chip as the lip bends. To prevent the chips from extending to the outer surface of the fender, you take a razor blade, and cut into th paint on the flat part of the lip, so when the paint cracks, it cracks in a straight line. Its best to use a little tough-up paint to seal the cracks when you are done. It will not be visible. I've also heard that if you use a heat gun on the paint as you are trying to bend the lip upwards, it will reduce/eliminate cracking of the paint.

NOT ALL 4th GENS ARE THE SAME, and not all tires are the same. Several people have managed to put the 17x11's on the back with no problems at all. Others have had to do everything that I mentioned above. There is no "correct" answer - each car is different.

(In process...... more to be added, including photo links)