Gearbox & RPM Calculator
Convert engine RPM to road speed through the gearbox and final drive, compare gear ratios and understand how they change acceleration and economy.
✔ 100% free
Mobile friendly
⚡ No account
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The drivetrain equation
Road speed = engine RPM ÷ (gear ratio × final drive ratio) × wheel circumference. Short ratios give acceleration; tall ratios give lower cruise RPM and better economy.
- Speed (km/h) = RPM ÷ (r_gear × r_final) × wheel_circumference(m) × 0.06
- A lower final drive (e.g. 4.10 → 3.73) lowers cruise RPM and fuel use, but slows acceleration
- RPM drops when shifting up; the calculator shows speed per gear
FAQ
The gear ratio is inside the gearbox per gear; the final drive is the axle reduction (differential). Total reduction = gear × final. Both affect speed for a given engine RPM.
A higher numeric final drive multiplies torque at the wheels, so the car accelerates harder but turns higher RPM at highway speed and uses more fuel.
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