[sphanna]

If you have 19" rims and Firestone 450/500 tires you will get 14,4" from center of hub to floor. Any other tires on 19 in wheels will be so close it will be negligible. Buy the way , Tom W. is correct in everything he said about the post. It is not complicated at all. But if you prefer, There is a very easy constant that will get you within 1 mph. That is to take your speed in mph and multiply it by 44 and you will have it. I was not able to calculate for 21" because I had not 21" wheels. Now I know since Tom has measured for us. Use his method and you will not go wrong. It is perfect.