Convert engine RPM into road speed using gear and final drive.
Engine speed is divided by the gear and final-drive ratios to get wheel speed, then the rolling tire circumference translates that into road speed. The same RPM gives very different speeds in different gears, so this is the quick way to sanity-check gearing and cruise RPM choices.
RPM to Speed
mph = RPM x pi x tire diameter / (gear x final drive x 1056)
mph = RPM x pi x tire diameter / (gear x final drive x 1056) Engine speed is divided by the gear and final-drive ratios to get wheel speed, then the rolling tire circumference translates that into road speed.
The same RPM gives very different speeds in different gears, so this is the quick way to sanity-check gearing and cruise RPM choices.
This calculator takes 4 inputs: Engine RPM, Tire diameter, Gear ratio, Final drive ratio. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.