Anti Skid Control

Anti-skid control, abbreviated ASC, is a manufacturer's trade name for an electronic system that prevents the wheels from spinning or sliding by managing traction and stability automatically. Rather than denoting a unique technology, the term describes a particular maker's implementation of what the industry broadly knows as traction control and electronic stability control. Different manufacturers brand essentially the same family of safety functions under their own acronyms, and ASC is simply one of these labels.

The purpose of such a system is to keep the tyres operating within the limits of available grip. When a wheel begins to spin faster than the car is actually travelling — typical of pulling away on a wet or icy surface — or when the car starts to slide sideways because the driver has asked for more grip than the tyres can supply, the system intervenes to restore order. It does so faster and more precisely than even a skilled driver could manage manually, because it is acting on data sampled many times per second.

The heart of the system is a set of wheel-speed sensors, the same ones used by the anti-lock braking system, supplemented on stability-capable versions by a yaw-rate sensor that measures how quickly the car is rotating about its vertical axis, a lateral-acceleration sensor and a steering-angle sensor. The control unit continuously compares where the driver is steering with how the car is actually moving. If it detects a discrepancy that signals a developing skid, it acts.

Intervention takes two main forms. To curb wheelspin the system reduces engine power, cutting the throttle or retarding ignition, and it can also apply the brake to the individual spinning wheel to send torque to the wheel with grip. To arrest a skid, the stability function brakes one or more specific wheels selectively — for instance braking an outer front wheel to counter oversteer — generating a corrective turning force that nudges the car back onto the driver's intended path. The driver simply feels the car settle, perhaps with a flickering dashboard light.

The scope of what a given ASC system covers varies by manufacturer: some brand names refer only to traction control, while others bundle the full stability-control suite. Functionally it is the equivalent of systems sold under names such as ESC, DSC and VSC, and it builds directly upon the anti-lock braking hardware. It is worth noting that no such system can defeat physics; it can only make the best of the grip the tyres have, so worn tyres or genuinely excessive speed will still exceed its ability to keep the car under control.