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In motorcycling, ABS can be defined as:
Anti lock braking system - a system which prevents the motorcycle wheels from locking up whilst under braking.
ABS has recently been introduced on modern motorcycles to help the motorcycle reduce its stopping distance under heavy braking. A motorcycle wheel will lose grip at a certain level of braking, therefore causing the motorcycle to skid. A rotating wheel gives the rider far more control over the motorcycle under heavy braking than a wheel with no grip, hence the introduction of ABS.
Especially useful on varied road surfaces (for example - slippery surfaces), ABS effectively reduces the braking power on the wheel (on a very minute scale) when it calculates that the wheel has lost grip on the road surface. In reducing the braking power, suitable grip levels are regained and the full braking power of the motorcycle can be used, all the while giving the rider as much control as possible.
ABS was first introduced on motorcycles in 1988 by BMW. Their BMW K100 example was quickly followed by Honda's ST1100 Pan European.
How it works: A typical ABS is composed of a central electronic control unit (ECU), two wheel speed sensors — one for each wheel — and two or more hydraulic valves within the brake hydraulics. The ECU constantly monitors the rotational speed of each wheel, and when it detects a wheel rotating significantly slower than the others — a condition indicative of impending wheel lock — it actuates the valves to reduce hydraulic pressure to the brake at the affected wheel, thus reducing the braking force on that wheel. The wheel then turns faster; when the ECU detects it is turning significantly faster than the others, brake hydraulic pressure to the wheel is increased so the braking force is reapplied and the wheel slows. This process is repeated continuously, and can be detected by the driver via brake pedal pulsation. A typical anti-lock system can apply and release braking pressure up to 20 times a second.