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Anti-lock braking systems

Over 70 per cent of cars manufactured in Europe come fitted with braking systems that prevent wheel lockup as standard.

india Updated: Aug 27, 2009 09:48 IST
Grease Monkey

Over 70 per cent of cars manufactured in Europe come fitted with braking systems that prevent wheel lockup as standard. Not much in that statement makes sense to the uninitiated, does it? ABS, besides being a type of plastic, stands for Anti-lock Braking System and not Anti-Braking System. If you’ve got the latter, you’re going to be in trouble soon enough.

A car moves thanks to the rotation of its wheels. If the wheels stop rotating, the vehicle stops. However, the laws of physics cannot be broken, so if the vehicle is travelling at a sufficiently high speed and the wheel stops rotating (‘locks up’), the vehicle’s momentum will keep it going for a while before it stops.

Locked rear wheels will make the rear of the car attempt to overtake the front, and locked front wheels will rob the driver of the ability to steer the car. A locked wheel is not a good a good thing, as this means that the driver cannot predict what the vehicle will do or control it, making for a dangerous situation.

ABS works in a very simple way: a computer is fed information about the speed of the vehicle, and the wheel’s rotational speed. If the relation between them remains within a set of parameters, all is well. If, however, the computer detects that the wheel is moving slower (or faster) than the vehicle’s body, then it recognises that something is wrong.

While braking, if the wheel slows down faster than the vehicle’s body, it means that the wheel is about to lock up, so the ABS releases the braking force on that wheel for a split second, then reapplies the brakes. This helps the vehicle retain control, and in certain conditions (like damp or wet roads), stop faster than with brakes not equipped with the technology. Some systems can apply and release the braking force to a wheel up to fifteen times a second!

This application and release of the system’s pressure can be felt in the brake pedal as a pulsation when the ABS activates. This isn’t a sign to lift off the brake pedal, merely keep your foot planted and your faith in the electronics.

ABS systems are of many types: the simplest ones use a single sensor fitted to an axle, and activate only if both wheels on the axle lock up. If only one wheel locks up, it does not activate the ABS. The best systems use a sensor for each wheel, so optimum braking is obtained due the system observing and judging each wheel independently.

There are a few surfaces on which an ABS-equipped car will take longer than a non-ABS car will to stop. On surfaces like gravel or snow, a locked wheel will build up a wedge of the surface material in front of the wheel, which slows the car faster than the ABS will allow, as the ABS keeps it rolling on top of the surface.

Unfortunately, ABS is a little expensive for our tastes, but you should know that the extra money you pay to add those sensors to your car costs the manufacturer much more, essentially making it a bargain — yet most of us don’t opt for it.

I once overheard a colleague, supposedly an automotive expert, advise a friend to not opt for ABS, because we don’t use it daily. That’s like saying, “Don’t purchase life insurance, you’re never going to use it in your day-to-day life.” The extra money you spend may safe a life — and that life may just be yours. Wouldn’t you consider that money well spent?

If you have questions or comments for Grease Monkey you can email him at with Auto Tech 101 in the subject line