The late, Ettore Bugatti once said, “I build my cars to go, not to stop!” when questioned about the near deadly lack of braking ability in his Grand Prix racers. Contrary to his opinion, brakes are a vital part of any car, be it a road car or a Grand Prix racer. Early automotive engineers had enough trouble getting their cars to move without worrying about stopping, nor did they need powerful brakes as cars built then were not capable of achieving high speeds.
In the early days, engineers mounted brakes on the propeller shaft rather than at the wheels. This put a tremendous amount of stress on a large part of the transmission between the brakes and the wheels. All they were trying to do was to avoid the complication of installing a brake unit inside the wheel. This became much easier later on as hydraulic systems came into place.
Even then, most cars upto the 1930s had brakes mounted only on the rear wheels. As you can imagine, these cars were not too stable under braking in corners, and emergency braking easily locked the wheels. Gradually, as braking technology improved, brakes were mounted on all four wheels and cable-operated systems were introduced. The next big step after this was the advent of hydraulic braking systems. Vacuum-assisted servos to reduce braking effort were introduced a little later.
Braking involves the conversion of the energy of motion into other kinds of energy. In normal braking systems, the kinetic energy of a moving car is transformed into heat energy that is allowed to escape. This heat is generated by the friction between the brake pads or shoes rubbing against the discs or drums. This friction makes the wheel slow down. Ultimately, the rate of slowing down depends on the tyres and the amount of grip provided by the road surface.
Slippery surfaces like ice or water-logged roads may cause a car’s wheels to lock-up under braking because of the lack of grip. This is where modern braking systems like Anti-Lock Braking (ABS) come into play.