GarageX calculators

Gear ratio & speed calculator

Gear ratio × final drive × tire size → road speed. See what RPM you'll turn at highway speed, or your speed at redline.

Engine RPM

Gear ratio

Final drive

Tire size

Road speed

56.9 mph · 91.6 km/h

…or RPM at a speed

Speed (mph)

Engine RPM

3,689 rpm

Engine RPM divided by the transmission gear ratio and final drive gives wheel RPM; multiply by tire circumference and you have road speed. Taller tires effectively lengthen your gearing (lower RPM at speed), shorter tires shorten it — which is why a tire size change shows up at the tach before anywhere else.