Final Drive Ratio Calculator

The final drive ratio is the gear ratio of the differential, found by dividing the number of teeth on the ring gear by the number of teeth on the pinion gear. For example, a 41-tooth ring gear and a 11-tooth pinion give a final drive ratio of 41 / 11 = 3.73, often written as 3.73:1. It sets how many times the driveshaft turns for each turn of the wheels.

A higher (numerically larger) final drive ratio multiplies engine torque more at the wheels, improving acceleration and towing, but raises engine RPM at a given road speed, which reduces fuel economy and top speed. A lower ratio does the opposite: relaxed cruising and better economy, but slower acceleration. Choosing a final drive ratio is a trade-off between acceleration and cruising efficiency.

The overall drive ratio is the transmission gear ratio multiplied by the final drive ratio. It gives the total gearing between the engine and the wheels in a particular gear. For example, a transmission first gear of 3.50:1 with a final drive of 3.73:1 gives an overall ratio of 3.50 times 3.73 = 13.06:1. The overall ratio determines engine RPM at a given wheel speed in that gear.

Ring and pinion tooth counts are often stamped on the ring gear or listed in the vehicle or axle specifications. The ratio is sometimes printed directly. If you only know the ratio, you can enter it by using any ring and pinion combination that produces it, since the calculator uses the ratio of the two counts. For an exact ratio, use the manufacturer's stated tooth counts.