Originally Posted by 04blackedge
Those calcs are right for me, with going from 29" to 32" it's off 5 mph at 60, speedo says I'm doing 55.
Don't forget. You speedometer is off by about 10%
So the faster you go the bigger the difference between indicated and actual speed. So at 70 indicated, your speed will be 77, at 80 = 88, etc. I almost got a ticket when I went past an AZ. hwy patrol car indicating 76 in a 75 and they clocked me at 84.