I own a 1988 IROC, which was ordered with the optional 16" wheels. According to information on this website, the 16" wheels had zero offset on the front and 16 mm offset on the rear.

Also according to information on this site, the standard wheel for the 1988 IROC was the 15x7 inch wheels. Questions:
1) Was there any offset on these 15 inch wheels?
2) Are the front/rear 15 inch wheels interchangeable? The 16 inch wheels are not.
3) What is the stock size tire for the 15 inch wheels on the IROCs?

The reason I ask is that I autocross my car. I must keep the car stock to stay in my class. I have the 2.77 rear on the car, which is a little too high for my purposes. While the obvious answer is to change the rear (3.23 was also available), I al thinking of getting the stock 15" to "reduce" the rear gear ratio.

Thanks

 

If you want to reduce the gear ratio, which I am assuming trying to have a numerically lower number, just get a taller tire, you don't have to get new wheels.

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'86 IROC
T-TOPS, TINTED WINDOWS, BRAKE LIGHT BLACKOUTS
GM GOODWRENCH 350
EDELBROCK TES HEADERS
3" Hooker CatBack w/Aero Chamber muffler
EDELBROCK 600CFM CARB.
KN AIRFILTER
ACCEL HEI DISTRIBUTOR
160* Stat
3:73 Posi
Rebuilt 700R4
B&M Megashifter, 5" Autometer Tach w/shift lite

 

Regardless of wheels size, the tire diameter is about the same. You won't affect the overall ratio. The 15x7's have no offset (are interchangable). Tire size is 235/60 or 216/65--not sure which one is stock.


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350 with stealth intake, holley carb, 470 lift cam. 700r4 with .5 boost valve, vette servo, tci lock-up kit, B&M megashifter. Richmond 3.73 gears, powertrax locker, timkin bearings, synthetic lube. Custom 3 inch single into 2 2.5 pipes. 1 1/2 drop springs, 1 5/16 solid front sway bar, 1 inch rear bar, custom subframe connectors, custom LCA relocation brackets. Kobel ground FX, currant red metallic paint. Lots of other stuff...
82camaro

 

Mark - No, I am looking for a numerically higher number (lower gear ratio) so a smaller diameter tire/wheel would be the way to go.

Unfortunately, 82camaro broke the bad news to me - Chevy made the stock aspect ratio on the 15" wheels to roughly yield the same diameter tire. Too bad. I guess I have to take a replacement rear end more seriously.

Thanks.