Not to split hairs, but I went from Goodyears to Michelins, and often times sizes will vary from manufactuer to manufactuer. It may just be the shape of the tires as well. The Goodyear was very "squared" and neat looking, whereas the Michelin is much more rounded the way the tread meets the sidewall. The tires look stretched on a Viper wheel, but then all smashed up on mine. I never measured both sidewalls, but it is a VERY noticeable difference in tire size, even looking at it from a distance.
When I swapped out the front tires, I went with the exact same size, just Michelin as opposed to Goodyear, and the sidewalls are taller on the fronts too.
2006 Corvette Z06
2" Stainless Works LT Headers
Random Technologies 3" X-pipe, with high flow polished cats
Callaway "Honker" cold air intake
Ported throttle body and intake
Custom dyno tune by MTI Racing Atlanta
496rwhp/478tq