Gear Ratio Calculator
Enter ring and pinion teeth to get your final-drive ratio, or type a ratio directly. Add tire diameter and engine rpm to see wheel speed and mph.
How to calculate a gear ratio
- Enter the ring gear teeth and pinion teeth, or type a known ratio.
- Optionally enter the tire diameter in inches and engine rpm.
- Read the final-drive ratio and the resulting road speed in mph.
Examples
Common 4.10 truck axle
ring = 41 teeth, pinion = 11 teeth
ratio = 3.73:1
Road speed in top gear
ratio = 3.73, tire = 26 in, engine = 3000 rpm
about 62.2 mph
Frequently asked questions
What is a gear ratio?
A gear ratio compares how many turns the driving gear makes per turn of the driven gear. An axle ratio of 3.73 means the driveshaft spins 3.73 times for each wheel rotation.
How do I find my axle ratio from the gears?
Divide the ring gear tooth count by the pinion tooth count. For example, 41 ring teeth over 11 pinion teeth gives 3.73, often sold as a 4.10 or 3.73 gear set.
Does a higher numerical ratio mean faster acceleration?
Yes. A higher ratio like 4.10 multiplies torque for quicker acceleration but raises engine rpm at speed, which usually lowers fuel economy and top-gear cruising speed.
How is mph calculated from rpm?
Wheel rpm equals engine rpm divided by the ratio. Multiply wheel rpm by the tire circumference, then by 60 minutes, and divide by 63360 inches per mile to get mph.
What tire diameter should I enter?
Use the overall loaded diameter of the mounted tire in inches, not the rim size. You can find it on a tire spec sheet or with a tire size calculator.
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