Antilock Brake System (ABS) Introduction

The Antilock Brake System (ABS) is designed to provide the driver with:
^ Optimal steering control and stability by enabling the vehicle to move in a driver controlled direction during braking.
^ Optimal braking performance by making the most of the available traction (on most road surfaces).

Wheel Slip
How well a vehicle can stop is related to how well the tire contact patch grips the road surface. At 0% slip, the tire rotates freely. At 100% slip, the tire and wheel are locked and the momentum of the vehicle pushes the locked tires along. Stopping distance increases and steering control lessens.

If the tires grip well (10%-20% slip), vehicle stopping distance will be as short as possible and steering control will be at its best. Some slip is necessary to stop the wheel and achieve maximum braking.

When ABS operation occurs, the driver of the vehicle should always continue to push hard on the brake pedal, but should never pump the brakes. The ABS will automatically moderate the brake pressure to keep the tires in contact with the road.

Steering Control
Steering control, like braking, also depends on tire traction. A locked tire in a 100% slip condition delivers less than optimum braking and directional control. Thus some tire rotation is desirable for steering control. The tires must regain traction before steering control is restored to the vehicle.