Once upon a time, Ettore Bugatti, when told his cars didn’t have good enough brakes, famously said, “I build my cars to go, not to stop.” Saying that today will probably mean marketing hara-kiri, since the brakes are automobile safety’s first line of defence.
Last week we saw how an automobile’s engine converts the energy in fuel to heat energy, which then puts the car in motion. This week, we’ll look at brakes, which do the same in reverse — they slow the car down by converting its kinetic energy (the energy it contains due to its motion) into heat energy.
If you’ve ever let your car coast in neutral — don’t try it in traffic, please — you’ll realise it can roll a fair bit before coming to a halt on its own. This is partly due to the momentum it generates thanks to its mass. Now technology has made tyres offer very little resistance to a moving car to better fuel economy. Look at a bicycle’s brakes, see how the brake pads rub against the wheel rim to slow it down?
Automobile brakes do the same thing by pressing two components against each other: one is stationary and the other is moving at the same speed as the wheel. The friction that is created generates heat, and this slows the car down.
Two main types of braking systems have been in use on automobiles: drum brakes and disc brakes. Most affordable cars in India have disc brakes fitted to the front wheels, and drum brakes at the rear. You can see the same setup on most of our larger India-manufactured bikes. Drum brakes have been in use on automobiles for over a century now, but technology has made them more efficient and better performers.
They consist of a ‘drum’, which is a cylinder that rotates at the speed of the wheel, with ‘brake shoes’ inside it.
These brake shoes are usually two pieces of hard-wearing, high-friction material that press against the inside of the drum when you hit the brakes. Drum brakes work fine for normal applications, but for high-performance applications, disc brakes have the upper hand.
Disc brakes have a metal ‘disc’ where the brake drum usually is, just inside the wheel on cars. The disc is also called the ‘rotor’. Since there is no inside for a disc, it is gripped by brake pads on either side. These pads are housed in the brake ‘calliper’, which is almost exactly like the brake pads on the bicycle brakes we talked about earlier.
Truck racers sometimes use drum brakes because of the weight advantage they offer over disc brakes, but everyone else in racing usually uses discs. On your car or motorcycle, you’ll find the discs at the front (if you don’t have them at the rear as well, that is).
They’re in front because under braking, the vehicle’s weight gets transferred to the front of the car. More weight on the front wheels means they’ll have more grip than the rear wheels. Therefore, it makes sense to have a more powerful stopping system at that end.
Be kind to your brakes; the best brakes can suffer from brake fade, which means they overheat and don’t stop as quickly as they normally do.If you find your brakes not performing as well as they should, get them checked as soon as possible. After all, they’re your first line of defence.
If you have questions or comments for Grease Monkey, email him at carsnbikes@
hindustantimes.com with Auto Tech 101 in the subject line