Tyre Adhesion
Tyre Adhesion The amount of the force applied on a shoe against a drum controls the resistance to rotation of a road wheel. Simultaneously the road surface has to drive the wheel around. This driving force attains its limit when the resistance offered by the brake equals the maximum frictional force generated between the tyre and road which is known as the adhesive force. This force can be determined from the expression : Adhesive force = Load on wheel x Coefficient of friction When the limit is reached, the wheel starts to skid, and any extra force on the brake shoe does not increase in the rate of slowing down the vehicle, no matter how good is the braking system. This means that the adhesion between the tyre and road is the governing factor for the minimum stopping distance. Road adhesion depends on : • Type of road surface. • Conditions of surface e.g. wet, dry, icy, greasy, etc. • Designs of tire tread, composition of tread material and depth of tread. The stopping distance of a