Automotive & Engines
Intermediate

Vehicle Speed from RPM

Road speed from engine rpm, gearing and tyre diameter.

Formula

v=πdNGR⋅Gfv = \frac{\pi d N}{GR \cdot G_f}

Variables

vSpeed
dTyre diameter
NEngine rpm
GRGear ratio
G_fFinal drive

Example

Lower rpm at a given speed means taller gearing and better economy.

Did You Know?

Tall final-drive ratios let motorway cars cruise at 120 km/h while the engine barely ticks over.

automotivespeedrpmgearing

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