The control unit then signals for reduced brake pressure, just enough to allow the wheel to start rotating again, thus preventing lockup. Understanding antilocks better requires knowing about the concept of wheel slip, or the speed of a vehicle's wheels in relation to the speed of the vehicle itself. When a car is rolling freely, without any braking, there is no wheel slip. That is, there is no difference between the speed of the vehicle and speed of its wheels. But when the wheels are fully locked, as in a skid, slip is at a maximum.
Wheel slip increases along with brake pressure.
Without antilocks, braking force rises to a peak and then falls as the wheels lock. What antilocks do is control the speed of the wheel to keep them away from lockup and maximize braking force. They do this by allowing brake pressure to increase until close to or just beyond the peak, then release the brakes until wheel slip is reduced and then apply them again. It continues until traction is restored or the driver releases the brake pedal. Because maximum braking is easy to achieve on dry roads with or without antilocks.