Braking force/tire slip

The braking force is equivalent to the coefficient of adhesion or the friction between the tire and the road surface. Each application of braking force gives rise to a certain degree of slip. The slip of a freely rotating wheel is expressed as 0% and of a locked wheel as 100%.

When the brake is first applied at 0% slip, braking force increases sharply but the degree of slip increases only gradually up to a certain limit. Beyond that point, braking force decreases with increasing slip.

Information on the rotational speed of each wheel comes from the wheel sensors. The TC/ABS control module measures the reference speed, normally on the fastest-rotating rear wheel. The reference speed is subsequently used to determine whether any wheel is exceeding the slip threshold.

Diagram 2: Lateral force as a function of slip.

Vertical axis = Lateral force

Horizontal axis = Slip

1. Lateral force
2. Stable braking zone
3. Unstable braking zone
4. Slip