I just purchsed a 87 camaro Iroc and will be fixing it up is being painted right now. I want to add chrome iroc wheel replicas. I saw some on line that had 18s in the back and 17 in the front . My question is , what would be a good tire size to go with. and will this mess up any of the transmission at all. thanks

 

Yes, the speedometer gear in the transmission will not be able to give the correct MPH unless you go with tires to manitain the stock diameter of the 50/16 tires..

 

And the odometer won't measure properly, and it'll affect your acceleration and fuel mileage as well.

Probably the closest you'll be able to get is a 45 sidewall on the 17s and a 40 on the 18s. There will still be a difference, but that's about as close as you can get, I think.

You can compare like I did using this site.
http://www.1010tires.com/tiresizecalculator.asp