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
- Lateral force
- Stable braking zone
- Unstable braking zone
- Slip