Anti-Lock Brake System Theory

The ability to slow or stop a vehicle depends upon the braking forces applied to the wheels and the frictional contact that exists between the tires and the road surface. Very low frictional forces exist when the tire is locked (or skidding). A locked tire also causes a loss or the lateral locating forces that effect directional control of the vehicle. The result of a locked tire (or tires) is the loss of steering control and stability. The major forces that affect how easy a tire will lock include:

• The braking force applied from the vehicles braking system.
• Environmental factors - rain - ice - snow - etc.
• Type and condition of the road surface.
• Condition of the tires (tread and design).

The anti-lock braking system is designed to allow the maximum amount of braking force to be applied to the wheels without allowing the wheels to lock or skid. The advantages that ABS provides includes:

• Driving stability - by maintaining the lateral locating forces between the tires and the road surface
• Steerability - allowing the driver to continue to steer the vehicle while stopping (even during panic stops) or accident avoidance maneuvers.
• Provides optimum braking distances - the rolling wheels transfer higher frictional forces to slow the vehicle.