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ABS Brakes

ABS Brakes

ABS or anti-lock braking system, is a computer module governing braking pressure in the event of drastic braking. The concept of the system is to avoid wheel lock-up and theoretically decreasing braking distance while maintaining steering response and stability under heavy braking.

Early ABS systems (late 80’s and early 90’s) worked on one axle alone, or on all of the wheels, in one channel, simulating human cadence braking. The system would detect when one of the four wheels locked-up and, after it was locked, would release all four tires nearly completely, and reapply in a rate similar to human pedal pumping. This, in turn, was highly inefficient and resulted in increased braking distances and crippled steering/stability. Furthermore, it did not manage to keep the wheels unlocked when surfaces were slippery or when grip was split (braking on two surfaces).

Newer ABS systems, like which we have in many cars to date (end of the 90’s, up to 2005 or so), have four, or at least three channels, thus being able to monitor each wheel individually (4-channel ABS), or each of the front wheels and both rear-wheels as one (3-channel ABS). Also, they do not release the locked-wheels all together, but monitor pressure to lock and unlock them, without releasing all of the braking pressure. However, in spite of the fact that these cars are able to remain nearly perfectly stable and sufficiently steerable in every condition, they actually still stop slightly (just slightly) further than locked-wheels when on high-traction tarmac. However, they do make the braking distance significantly shorter in slippery conditions. A problem of these systems is their very noticeable activity. At work, these systems can create pulsation in the brake pedal, juddering of the steering wheel and chassis, and distracting noises. This is particularly noticeable in wet conditions, where the system works harder. This is natural, helps in braking, and actually makes braking more technically friendly to the car’s components in general.

Latest ABS systems, are able to perform in great proximity to threshold braking, being able to completely avoid wheel lock-up, keep the car braking at the threshold for most of the time, and stop it quicker on almost any surface. This ABS system does not mimic cadence braking, like many people believe (which held true for the older systems). The one place where ABS (and threshold braking) carry increased braking distances, is on soft surfaces, typically soft gravel, and sometimes even a bit of fresh snow. However, ABS or threshold braking, still enable steer-ability and stability. In the latest systems, the advantage of steer-ability and stability is decreased in sake of a shorter braking distance. This can be seen when braking in split-grip scenarios. With all ABS systems, steering response is crippled somewhat, and input should be issued carefully and accurately.

Regardless of the type of ABS fitted (if at all), it is suggested that in relation to braking before a corner on the track, that you use threshold braking with a regressive approach: apply the foot-brake rapidly, but not quite stomping on it at once, until the threshold where ABS is about to kick-in or when the wheels are about to lock-up. Now, gradually modulate the pressure (generally this means constantly and controllably releasing pressure as you go), to keep the car at threshold braking. This will slow you down more efficiently.

An emergency is approached differently, even for professionals where the advice is to immediately stomp the brakes, and let the ABS or locked-wheels slow you down to a halt. Even without ABS, modern cars tend to remain highly stable, because the inertia is pushing them dead ahead. A normal phenomenon is for the car to rotate slightly (typically no more than 45 degrees) around it’s own axle, making it look as though if it is swerving or about to spin. However, regardless of the amount of rotation (which should be minimal, even on slippery or split grip conditions), the car would keep on going straight forward.

In this context it should be mentioned that ABS commercials tend to display these physical issues as problems. In these commercials, cars without ABS are made to brake significantly further away, or rotate far more than they should (80 degrees, 360 or even ten spins). This is caused by playing around with tire pressures, or by using special skid-pans, sometimes presented as merely wet surfaces but actually include a white line made of a highly slippery surface (similar to ice) thus simulating a condition of split-grip, which is far more acute than any realistic situation. Normally, split-grip braking in emergencies is done with two wheels on a gravel or grassy shoulder, or on a slightly more frozen or wet part of the road.

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