Your car is probably equipped with one of these safety assistants, but what is the difference between them?


All new passenger vehicles sold in the European market since 2014, or in the USA since 2012, are required to have electronic stability control fitted as standard equipment. This electronic safety aid is not mandatory in South Africa, however, enabling importers to sell car from developing markets here, because those markets are similarly free from this requirement.

What is traction control?

When the torque on the driving wheels exceeds the tyres’ mechanical grip limits, the contact patch will be subjected to large-enough forces to cause slippage between the tyre and the road surface. This is typically more common in lower gears and higher-powered cars, but even vehicles with relatively little power can easily overcome the traction limits on less-than-ideal surfaces. This creates an obvious safety hazard, because spinning drive wheels could easily become the first step towards losing control of the vehicle.


To alleviate this problem, manufacturers devised some methods to momentarily reduce the engine’s output when the wheelspin is detected. In some early cases, the ignition of random cylinders were cut, which induced a misfire to reduce the torque. However, this practice soon fell out of favour due to potential damage to the catalytic converters.

The next step entailed reducing output by closing an extra throttle butterfly, effectively depriving the engine of air when wheelspin is detected. Early BMW and Lexus traction control systems used this arrangement, where the air supply to the engine’s throttle body could be reduced by closing a secondary throttle valve in the air stream before the intake manifold. Later engines with electronic throttle control (drive-by-wire throttle) eliminated the need for additional butterfly valves, greatly simplifying traction management.


This approach has one major disadvantage, however, because it is a reductive system. Rather than manage the available power according to the road conditions, it simply reduced power to adapt to adverse road surfaces. And, on very slippery roads, this could simply result in the car not moving at all - that's why it's usually possible to switch off such systems, at least temporarily.