Gearing Calculator
Your speed at any RPM, for any gear, with any tire size.
Road speed
96.2 km/h(59.8 mph)
- Wheel RPM
- 804
- Tire OD
- 634.3 mm
- Tire circ.
- 1.993 m
- Combined ratio
- 3.73
Typical usage: enter your cruise RPM (like 2,500 in 6th on the highway) and see your actual speed. Change the final drive to simulate a regear.
About this calc
Calculate vehicle speed given engine RPM, transmission gear ratio, final drive, and tire diameter — or work backwards from speed.
FAQ
- How does changing the final drive affect my car?
- Lower numerical ratio (e.g. 3.73 → 3.23) = taller gearing = lower RPM at highway speeds, better MPG, slower acceleration. Higher ratio (3.73 → 4.10) = snappier acceleration, higher cruise RPM, worse MPG.
- Why does my new, bigger tire feel slower?
- Bigger tire = longer wheel circumference = fewer revs per mile = effectively taller gearing. You lose acceleration but gain cruise efficiency.
- How do I calculate RPM for a target speed?
- RPM = (speed_km/h × 1000 × gear × finalDrive) / (60 × π × tireOD_m). Or just plug in guesses in this calc until the speed matches.