Hi, this is my 2nd vette its a 01 Z06 w/ 15k. When I bought it I had them switch my wheels to the new car. Better tires. My 99FRC had 275/40/18's the z06 had 295/35/18's. Due I need to recalibrate for the different circumference.
There is a tire size calculator/conversion table on one of the large tire retailers website. I would mention their name, but if they are not a sponsor it is a no no. Instead I will give you the results your P295 tire was spinning at more revolutions because its overall diameter is less the the P275. Your vehicle when traveling at an indicated 65 mph is actually moving at 66.7 mph.