Fitted as standard on all BMW models, ABS prevents the wheels from locking when braking at the limit :

There is a speed sensor at each road wheel. The signals from the sensors are applied continuously to a central electronic unit. If the rotation speed of one wheel suddenly drops by an above-average amount, the electronics identify this as a risk of the wheel locking, and reduces hydraulic pressure in the corresponding brake line momentarily until the wheel rotates freely again.

This control cycle can be repeated many times a second if necessary. The driver hears a signal and feels a pulsation at the brake pedal as a sign that the ABS is in use.

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