Factors Associated with Controlled Stopping of the Vehicle
A. Vehicle weight
1. The more weight a moving vehicle has, the more kinetic energy
it will possess. Brake systems must convert kinetic energy into heat; therefore any increase in vehicle weight will put more demand on the brakes.
2. If a vehicles weight is doubled the amount of kinetic energy that the brakes must convert into heat is doubled. The amount of heat energy resulting from the conversion will also be doubled. Brakes on an overloaded vehicle may, therefore, become in effective due to overheating.
B. Vehicle speed
1. When the speed of a vehicle doubles, the brakes must convert four times the amount of kinetic energy into heat. Speed greatly increases the demand on a vehicle's brakes. 2. A combination of high speed and excessive weight may push a vehicle's brakes beyond their performance limit resulting in a serious loss of stopping power.
C. Friction between tire and road
1.The point at which a vehicle's tire contacts the road is called tire footprint. Changes in tire footprint affect a vehicles ability to stop. Below is a discussion of the factors affecting tire footprint.
a. The larger a tire's diameter, the larger its footprint. The larger the tire footprint, the more stopping power that can be applied at the tire's contact point with the road. It is important to realize however, that the greater a tire's diameter, the more braking power that is needed.
b. The greater the width of a tire, the larger the footprint. The larger the footprint, the more stopping power that can be realized; however the greater a tire's width, the more braking power that is needed to stop.
c. Excessive vehicle weight can distort tire tread and thus reduces the tire's hold on the road; tires that cannot hold the road will reduce the vehicle's ability to stop.
d. High vehicle speed can aerodynamically lift a vehicle as it moves. This lifting reduces the tire's hold on the road, thus reducing the vehicle's ability to stop.
e. Tires grip the road more securely if the wheels are moving; therefore stopping power is decreased if the brakes lock up. The wheels automotive engineers are careful not to design brake systems that are too powerful for the cars in which they are installed. If a brake system locks up the wheels too easily, stopping power and vehicle control are significantly reduced.
