I've got a 16, hits the limit at 42 on speedo, with stock tires that was 37 actual on GPS. After swapping to 27" tires it'll do 41 on GPS at the limiter. A friend has a 17 and swears it only hits 36-37mph on the speedo at the limiter. Anyone else have this happen?
To the OP, I was concerned about the weight of the tires when I ordered also but the P5 has such low gearing to start with it does fine. I still start out in 2nd, if anything I think the extra weight helped smooth out the power delivery, shifting, etc.