e of the road is not level. Then again, a car may spin out. In any of these cases, the driver has effectively lost all control over the direction the car will travel. Antilock brakes can help with these problems but how much depends on the road surface. Anti-locks don't make much difference in stopping distances on dry roads because maximum braking is easy to achieve on dry roads with or without anti-locks. Even if the wheels lock, the coefficient of friction between the tires and road surface is still fairly high so a vehicle stops relatively quickly. The most pronounced improvement occurs on slippery surfaces where the drag factor is low. Here, anti-locks can significantly reduce stopping distance and prevent loss of control. III. Understanding ABS There are several types of antilock brake systems but they all operate similarly. Sensors near each wheel monitor rotational speed and, as the brakes are applied and the wheel slows, an electronic control unit determines when any wheel is about to lock. The anti-locks will then automatically pump the brakes at a rate of up to 18 times per second to prevent wheel lockup. Understanding anti-locks better requires knowing about the concept of wheel slip, or the speed of a vehicle's wheels in relation to the speed of the vehicle itself. When a car is rolling freely, without any braking, there is no wheel slip. That is, there is no difference between the speed of the vehicle and speed of its wheels. But when the wheels are fully locked, as in a skid, slip is at a maximum. Wheel slip increases along with brake pressure. Without anti-locks, braking force rises to a peak and then falls as the wheels lock. What anti-locks do is control the speed of the wheel to keep them away from lockup and maximize braking force. They do this by allowing brake pressure to increase until close to or just...
