#8765, "RE: will bigger wheels always make you slower, and other ?" In response to In response to 5
>^^^it's impossible to get the diameter of the tire on the >wheel exactly the same because the heightof the tire is >measured in percent. and not all tires of the same size are >the exact same height.
True, but like joshacu said, the difference is miniscule. My stock tire was 205/55/16. The outer circumference is 78.1564". My 225/40/18's have a circumference of 78.811" which turns out to be 0.84% difference. That means when my speedo says 80, I'm actually doing 80.6 mph. Our speedo is not nearly that accurate, so the difference is negligible.
As long as your tire size is pretty close, the gains/losses from a difference won't be seen on the dyno or the track. However, the difference from the weights of the wheel/tire combo due to size of wheel etc. will be seen in both places.
