How to Come Up With a Differential Ratio

A differential consists of two gears.

A differential is a set of metal gears. If you have a vehicle, such as a lawn mower or a rear-wheel drive automobile, your vehicle has a differential. The large gear inside the differential housing is the ring gear. The smaller cone shaped gear inside the differential housing is the pinion gear. Differential ratios are denoted as a decimal number. For example, a 4.11 differential, commonly used in vehicles that require high torque has 37 teeth on the ring gear and 9 teeth on the pinion gear. There is a simple way to come up with the gear ratio for the differential in your vehicle.

Instructions

1. Count the teeth on the larger ring gear and write down the number.

2. Count the number of teeth on the smaller cone shaped pinion gear and write down the number.

3. Divide the total number of ring gear teeth by the total number of pinion gear teeth to obtain the ratio.

Tips & Warnings

• As a practical example, assume your ring gear has 45 teeth and your pinion gear has 13 teeth. Written as a standard ratio you have 45:13 gear teeth ratio. The differential ratio is 3.46 after you divide 45 by 13.

References

• Jedi: How to Determine Your Axle Gear Ratio