How this calculator works
Divide engine speed by both reductions to get wheel speed. Each wheel revolution advances the vehicle by one rolling circumference. Use effective rolling diameter, which can differ from an unloaded sidewall size. The model assumes a fully engaged clutch or locked converter, no tyre slip and no additional transfer-case reduction. Include additional fixed reduction in one of the entered ratios if required.
Formula
v = pi D RPM / (60 Rt Rd); wheel RPM = engine RPM/(Rt Rd).
Worked example
A 1 m rolling diameter, 3000 engine rpm, 2:1 transmission and 5:1 differential give 15.707963 m/s. At 31.415927 m/s with a 1:1 gear and 4:1 differential, the engine turns 2400 rpm.
Advertisement
Frequently asked questions
Can a transmission ratio be below one?
Yes. A numerical ratio below one is overdrive using this reduction convention.
Why does measured speed differ?
Rolling diameter, slip, tyre growth and instrument error can all change the result.
Does this calculate acceleration?
No. Acceleration also requires torque, mass and resistance forces.