Sprocket and Chain Ratios: Sizing Drive Ratios for Motorcycles

Motorcycles typically use a chain and sprocket system to transmit power from the transmission output shaft to the rear wheel. Changing sprocket sizes is an easy way to tune a motorcycle's acceleration and top speed.

The Sprocket Ratio Formula

The sprocket ratio is calculated by dividing the number of teeth on the rear sprocket by the teeth on the front (drive) sprocket:

$$\text{Sprocket Ratio} = \frac{\text{Rear Sprocket Teeth}}{\text{Front Sprocket Teeth}}$$

For example, a motorcycle with a 15-tooth front sprocket and a 45-tooth rear sprocket has a ratio of 3.00. Installing a smaller front sprocket or a larger rear sprocket increases the numerical ratio, improving acceleration but reducing top speed.

Calculate sprocket ratios and wheel speeds using our automotive gear ratio calculator. For torque calculations, read our guide on torque multiplication in gearboxes.