By chance, does anyone know what size tires came stock on a 2001 Z28?

I am trying to figure out the difference in final gear ratio going from the stock size (which I don't know) to a 275/35ZR18 (Z06 rims).

The reason being, the previous owner had a Hypertech programmer and had the gear ratio listed as a 3.23. The car is an M6, and I know it has 3.42 gears. But with going to a taller wheel and tire combo, I know it would make the gear ratio "feel" less than 3.42.

I want to make sure his 3.23 setting didn't make the odometer run slow.