RPM formula
this is an easy formula that seems to work....
MPH x Gear Ratio x 336 divided by Tire Diameter(inches)
say 100 mph, 4.86 gears, 30" tires.....= 5443 RPM
if you want to get fancy, you can add an inch or whatever for Tire growth, and add 5-10% for convertor slippage.....anyways, it works!