Wheelspeed

Wheelspeed is the rotational speed of a wheel around its axis. It is commonly measured in revolutions per minute (RPM) or radians per second, and it relates to the vehicle’s forward speed through the wheel’s effective circumference. A simple approximation for vehicle speed v is v ≈ (π × D × N) / 60, where D is the wheel diameter in meters and N is the wheel speed in RPM.

Modern vehicles typically measure wheel speed with wheel speed sensors located at each wheel. These sensors often use a Hall effect element with a toothed reluctor or an optical sensor that produces pulses each time a tooth or mark passes. The vehicle’s electronic control unit uses the pulse frequency to compute the wheel’s RPM for each wheel.

Wheel speed data are central to several systems. Anti-lock braking systems monitor individual wheel speeds to prevent excessive lock-up by modulating braking pressure. Electronic stability control compares wheel speeds to the vehicle’s yaw and lateral behavior to adjust braking and engine output. Wheel speed information is also used to derive the vehicle’s speed for the speedometer and cruise control, though some designs obtain speed from the transmission instead.

Wheel speed can be affected by tire size, inflation, and load, which change the effective wheel circumference. During acceleration, braking, or turning, wheel slip may occur, causing the actual vehicle speed to diverge from wheel speed. Accurate measurement requires calibration and is essential for safe operation of braking and stability systems.

Related topics include tire rolling radius, anti-lock braking systems, traction control, and vehicle dynamics.