Attached is a simple Excel spreadsheet file that will calculate gear ratio, final drive ratio, rollout, etc. If you wish to input the internal gear ratio it can make the calculations, or your can enter the number of teeth for the rear diff and the center pulley (leave the “Int. Ratio” field blank or “0”) and it will perform the calculation based on this input. If you put in a number for the “Int. Ratio” it will use this number and ignore rear diff and center pulley numbers.

Supply input ONLY in the yellow shaded areas.

If you input “Tire Diameter” in millimeters (mm), than the rollout will be in millimeters (mm).

If you input “Tire Diameter” in inches (in) (decimal format only), than the rollout will be in inches (in).

If you wish to make the table bigger, just copy the bottom row down as many times as you want.