A gear ratio compares the input and output of a gear set, showing how it trades speed for torque.
Gear Ratio = Driven Teeth ÷ Drive Teeth
Where
| Driven teeth | Teeth on the output (driven) gear |
| Drive teeth | Teeth on the input (drive) gear |
Worked example
A 40-tooth gear driven by a 12-tooth gear gives 40 ÷ 12 = 3.33:1 — the output turns once for every 3.33 input turns, with 3.33 times the torque.
Overall ratio: multiply the transmission gear ratio by the axle ratio to get the final drive at the wheels.
Use the Gear Ratio calculator in the automotive calculators, and read How to Calculate Gear Ratio.