Definition of traction control in cars

Written by graeme kay
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Definition of traction control in cars
Traction control makes driving in wet conditions safer. (driving in dangerous conditions on a wet road image by Stephen Gibson from

Traction control is an electronic and/or mechanical safety system that is now fitted to most new cars. Different manufacturers give the system different names, but the aim is always the same---to automatically intervene to maintain the best possible contact between the car's tires and the road surface.

Traction Science

Traction control is important because a car tire can only offer a certain amount of grip. This is split between longitudinal grip (used for braking and accelerating in a straight line) or lateral grip (required for cornering). Without a traction control system, drivers have to constantly judge the combination of acceleration, braking and cornering that their cars can achieve without losing grip and compromising safety. Wet, icy or muddy roads add another factor that drivers have to take into consideration. Traction control systems take this balancing act out of the hands of drivers, preventing them from getting into situations where they might lose control of their vehicles.

How It Works

Most traction control systems were developed from anti-lock braking systems designed to stop cars' wheels locking up and losing grip with the road under heavy braking. Rather than monitoring when a wheel has stopped turning, traction control aims to spot when one or more wheels are turning more quickly than they should for the speed of the vehicle---an indication that traction has been lost. If loss of grip occurs, traction control will use a combination of brake and/or engine control to try and maximise the available traction for any road surface. This process will typically involve braking at one or more drive wheels, fuel injection cut-off, ignition spark retardation or air/fuel ratio control.

Early Systems

One of the first traction control systems was called MaxTrac. Available as a £65 option on Buick's Riviera models between 1971 to 1973, it consisted of a speed sensor in the left front wheel hub and a second speed sensor mounted on the transmission and interconnected with the speedometer drive and a solid-state electronic controller. The controller compared the inputs from the two sensors; if the driven sensor at the transmission indicated a higher speed than the sensor mounted on the front wheel (suggesting wheel spin), the MaxTrac would intermittently interrupt the ignition system to reduce the power applied to the drive wheels to bring the car back under control.

Current Systems

As noted earlier, different car manufacturer offer their traction control systems under different names. Ford, for example, offers the All-Speed Traction Control system that uses components of the anti-lock braking system to monitor wheel slippage at any speed. BMW offers Dynamic Traction Control on its 3-Series cars. This system can be adjusted offering different levels of wheel slip for different surfaces, or turned off altogether if the driver wants to test their driving skills to the limit. Toyota's TRAC traction control system is another all-speed design that utilises both brake and engine throttle control to help avoid slippage of the driving wheels.

Motor Sport

Motor sport was an early adopter of traction control systems, although for a slightly different purpose. Rather than ensuring stability under everyday use, in racing cars the aim is to get the maximum amount of power to the road at all times. Cars competing in the Formula 1 championship used the systems in the 1980s and early 1990s, although it was then banned. The system was reintroduced in Formula 1 from the start of the 2002 season, only to be outlawed again from the start of the 2008 season.

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