Gear Ratio Calculator
Find the axle gear ratio from ring and pinion teeth, plus the engine RPM at a given speed.
How it works
Gear ratio = ring teeth ÷ pinion teeth · Engine RPM = speed × (63360 ÷ (π × tire) ÷ 60) × ratio
The axle (final drive) ratio is simply the ring gear teeth divided by the pinion teeth — a 3.73:1 ratio means the driveshaft spins 3.73 times for every wheel revolution. To find engine RPM, the tire’s revolutions per mile set the wheel speed, which the gear ratio multiplies up to the engine. This assumes a 1:1 transmission gear (typical of a direct top gear); overdrive gears would lower the RPM.
Worked example
A 41-tooth ring and 11-tooth pinion give 41 ÷ 11 = 3.73:1. With a 28-inch tire (about 720 revolutions per mile) at 65 mph in a 1:1 gear, the engine turns roughly 2,900 RPM.
Frequently asked questions
What does a numerically higher gear ratio do?
A higher ratio like 4.10:1 gives quicker acceleration and more pulling power but raises cruising RPM and lowers fuel economy. A lower ratio like 3.08:1 relaxes highway RPM at the cost of low-end punch.
How does tire size change the result?
Larger tires cover more ground per turn, effectively lowering the gearing — engine RPM drops at a given speed. Many people bump to a numerically higher axle ratio after fitting bigger tires to restore the feel.
Why assume a 1:1 transmission gear?
Direct-drive top gears are often 1:1, which makes the axle ratio the whole story. If your top gear is an overdrive (below 1:1), multiply the RPM by that gear ratio to get the real cruising figure.
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This calculator is for educational purposes. Double-check important results before acting on them.