Reduction & axle overdrive

Follow every reduction from motor to tire, once.

Shared reduction stages

Everything before the front/rear split: pinion and spur, transmission, transfer case. Use 1 for a direct stage. Portals go in the axle ratios below.

Stage 1 reduction

After the axle split

Both ratiosStock + changes

Front axle reduction

Rear axle reduction

Front tire diameter

Rear tire diameter

Measured or assumed motor RPM

rpm

Front versus rear

Enter one to eight positive shared reductions, positive axle ratios and tire diameters, and nonnegative motor RPM.

Overdrive assumes equal transmission outputs. Positive means the front runs faster. Gear-set listings often print the ratio-drop number instead, which is the smaller of the two. Contact-patch speed folds in tire size. These are axle speeds without slip, not vehicle speed.