im not sure of the RPM mainly because i was more concerned with keeping my car as stable as possible and reaching the aerodynamic limit. My wheels and tires are the the same diameter as the stock wheels and tires, so that should not cause a MPH difference as far as i can see, the only thing the tires should affect is the added friction that the extra surface area creates but this is such a small number that i doubt it really comes into play at this point. I was doing 150 on a local highway I-71 North in cincinnati very late at night and was very careful to make sure the road was clear. And i am well aware of the risk's that i faced.