Modern Car Brakes

Modern Car brakes were invented in the late 19th century, around the same time as the tyre. Up until then, vehicles had wooden wheels that were stopped by large wooden blocks, lowered into position by the driver using a simple lever system. When tyres were invented, the wooden block system wasn't good enough to stop them at the higher speeds they could achieve, which meant that a new braking system had to be invented.

The braking system is the most important system in the car. If the brakes fail, the result can be disastrous. The brakes are in essence energy conversion devices, which convert the kinetic energy (momentum) of your vehicle into thermal energy (heat).

In recent years, brakes have changed greatly in design. Disc brakes, due to their lighter weight and better performance, are replacing drum types on the rear wheels. Instead of linings which press outwards against the inside of a drum, a disc attached to the axle is gripped from either side by friction pads attached to the calipers. The greatest advantage of disc brakes is that they are essentially "fade" free. That is, repeated application does not result in excessively high temperatures developing in the linings and drums, lowering the stopping power of the brake. Commonplace on newer cars are "anti-lock" brake systems, (ABS) which prevent the wheels from completely stopping when the brakes are applied in a panic stop.

To see the basic principles of modern braking, it is easiest to look at a bicycle. Basically, when you put pressure on the brakes, the pressure is transferred through cables to pull small pads onto the side of the tyres, and the force of the friction against the tyres causes them to stop.

In fact, cars originally used this very same cable system, but it was found not to work so well at high speeds. Instead, the cables were replaced with hydraulic fluid, which works to transfer the pressure the driver puts on the pedal to the brakes. This works because the fluid cannot get much smaller when pressure is put on it, meaning that pressure at one end is transferred to the other much like water flowing through a pipe. However, if this brake fluid leaks even a little, then the brakes may not work properly any more, which is why it's very important to check your brake fluid regularly.

Of course, in modern cars, there are other mechanisms apart from pure pressure to help you brake. Most cars now have a vacuum system to create more friction in the brakes, and a servo system that uses the car's own speed to help your pressure have more of an impact.

Some modern cars now have fully computerised brakes, where pushing on the pedal sends an electrical signal to turn on electrically-powered brakes. While this makes it much easier to brake, it is also more prone to failure, meaning that if your car's computer breaks you might find it impossible to stop.