Here's the formula for using excel to calculate revs per mile:
Copy and paste the above formula into cell D2. Then enter tire width into cell A2, aspect ratio into cell B2, and wheel diameter in cell C2.
In case your real dumb:
305 is the tire width in millimeters
70 is the aspect ration (sidewall height is 70% of tire width)
16 is the wheel diameter in inches
Haggar, you might want to add this to your revs per mile tab.