Gear Ratio Calculator
Work out axle ratio and the cruising RPM it produces.
How this calculator works
ratio = ring teeth ÷ pinion teeth · RPM = mph × ratio × 336 ÷ tire diameter
The 336 constant folds together the conversions from miles per hour to inches per minute. This assumes a 1:1 top gear — multiply by your overdrive ratio if the transmission is not direct.
Worked example
With ring gear teeth 41 , pinion gear teeth 11 , tire diameter 31 in, cruising speed 70 , this calculator returns 3.73 .
Frequently asked questions
What gear ratio should I run with larger tires?
Taller tires effectively raise the gearing, so you need a numerically higher ratio to compensate. Going from 31 to 35 inch tires typically means moving from 3.73 to 4.10 or 4.56 to restore the original feel.
Does a higher gear ratio mean more power?
More torque multiplication at the wheels, not more engine power. A numerically higher ratio improves acceleration and towing at the cost of higher cruising RPM and worse fuel economy.
How do I find my current gear ratio?
Turn the driveshaft and count how many rotations it takes for the wheels to turn once. Three and three quarter turns means roughly a 3.73 axle. The tag on the differential also carries it, if it survives.
What is a good highway gear ratio?
Something that puts the engine between 1,800 and 2,200 RPM at cruise for a modern petrol engine. Much lower and it lugs; much higher and fuel economy suffers noticeably.