Find engine RPM at any speed - or find the speed at a given RPM - using your transmission gear, final drive, and tire diameter.
Don't know your tire diameter? Use the Tire Size Calculator first.
| Speed (mph) | Engine RPM |
|---|
Enter every gear (or load a transmission preset above - it fills these too) and your redline to see top speed in each gear and the RPM you land at after every upshift.
Uses the final drive and tire diameter from the inputs above. Leave unused gears blank. Top speed in the last gear is gearing-limited speed - real top speed is usually drag-limited first.
Your engine's RPM is determined by how fast the wheels are spinning, multiplied by all the gear reductions between the crankshaft and the tire contact patch. The formula uses two ratios: the transmission's ratio for the selected gear, and the final drive (differential) ratio.
Where Total Ratio = Transmission Gear Ratio × Final Drive Ratio and the constant 336 accounts for unit conversion (miles per hour → inches per minute → revolutions).
A numerically higher final drive ratio (e.g., 4.10 vs 3.23) multiplies torque to the wheels more aggressively, improving acceleration but raising RPM at cruise speed and hurting fuel economy. Swapping final drive gears is one of the most effective ways to tune the power delivery character of a car.
A taller tire effectively lengthens your gear ratios - your RPM will drop at any given speed, which can make the car feel lazier off the line. A shorter tire has the opposite effect. Always recalculate after a tire size change.
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