I have been doing a little it of research on tire and wheel sizes and I had an interesting (at least to me it was interesting) thought.

According to the calculator at miata.net (http://www.miata.net/garage/tirecalc.html) a 245/45/17 tire makes 785 revs per mile while a 235/40/18 makes 794 revs per mile. If the computer is not adjusted accordingly not only will the speedometer be in accurate but so will the odometer. Furthermore, this would result in a premature exhaustion of the vehicles warranty (by approximately 400 miles) and an increased rate of depreciation of my vehicle.

So the question stands when I purchased my GTO with the 18 inch wheels, did GM adjust the computer for these wheels?

So the question stands when I purchased my GTO with the 18 inch wheels, did GM adjust the computer for these wheels?

I certainly hope so, because I too have the 18" wheels. I assume the contention is that the diameter of the wheel plus tire for the 18" wheels is less the same for the 17" wheels?

-K