Vehicle Speed Calculator
Calculate theoretical vehicle speed from engine RPM, tire diameter, transmission gear ratio, final drive ratio and driveline slip.
Calculator
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mph
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Formula
mph = RPM × tire diameter(in) × π ÷ (gear × final drive × 1056) × (1 − slip/100)
Input definitions
- RPM: engine speed in revolutions per minute.
- Tire diameter: nominal overall tire diameter in inches.
- Gear ratio: transmission ratio for the selected gear.
- Final drive: differential/final-drive numerical ratio.
- Driveline slip: assumed percentage loss between engine speed and tire speed.
Worked example
At 3,000 RPM, a 26-inch tire, 1.00:1 gear, 3.73:1 final drive and 0% slip gives approximately 62.2 mph.
Assumptions and limitations
The result is theoretical. Actual road speed can differ because of loaded tire radius, tire growth, inflation pressure, torque-converter or clutch slip, drivetrain compliance, measurement error and other vehicle effects. Use measured data when validating a vehicle.