Discover the disc brakes

This post is all about the disc brakes. We will discuss about their working and will also try to answer some very interesting questions related to them. Disc brakes have become common these days. They are  replacing the traditional drum brakes due to multiple advantages, they have over them. Lets first understand the working of disc brakes.

Working of disc brakes

Brake caliper

Disc brakes have a disc fitted with the wheels. The disc rotates along with the wheel. The braking effort is transferred through hydraulic fluid. When brake is applied the hydraulic fluid moves to the brake calipers, where it forces the piston to move outside. The piston top contain brake pads. These pads press against the disc and try to decrease its speed.  This friction force causes the wheels to deaccelerate and help ultimately in stopping the wheel.

Advantages of disc brakes

The disc brakes have following advantages:

1. They dissipate the heat easily

Since the disc is completely in touch with environment, it looses the heat generated by the friction easily. While the drum brake assembly is completely covered inside the drum. So they can not dissipate the heat easily.

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2. Easy inspection

Drum brake

As the disc brake system completely lies out side, it can be inspected easily without removing any part. Also it can be cleaned and parts can be replaced  easily.

3. Efficient braking

The disc brakes generally use hydraulic system to transfer brake force. So a much larger braking force can be transferred easily to the brake pads. Also the brake pads in disc brakes are flat while those in drum brakes are curved. The flat pads transfer the brake  force more uniformly and distribute equally over the contact surface. The wear of the pads is also more uniform for the flat pads.

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4. Light weight

The disc brake system is lighter as compared to the drum brakes. This helps in overall weight reduction of the vehicle.

Why the disc brakes are used mostly on front wheels?

You might have noticed that the disc brakes are used generally on the front wheels. Do you know the reason behind it? Let me tell you. The motorcycles having single disc, have them on the  front wheels only. Even the cars generally have disc brakes on front wheels and the drum brakes on the rear. The main reason behind it is weight transfer during the braking. At the time of braking the inertia of the vehicle causes the shifting of most of the weight on the front wheels. This increases the normal reaction of ground on the front wheels which further increases the friction between the ground and the wheels. This increased friction between the ground and the front wheel increases the braking effectiveness and decreases the stopping distance. The higher friction between the wheel and the ground also prevents the slipping of the wheels. The reason behind using disc at front while drum at rear has economical aspect also. The disc brakes are costly as compared to the drum brakes. So to have effecting braking without increasing the cost excessively, disc brakes are generally used on the front wheels only. 

Why the disc of motorcycles have holes on them?

Drilled holes on disc

You might have noticed the holes on the disc of motorcycles. There are not just fancy or designer stuffs. They are made for a reason. The reason being effective heat loss. Yes, they are made to increase the rate of heat loss from the disc. During the operation of brakes very high amount of heat is generated due to the friction between the brake pads and the disc. This increases the temperature of the disc and the brake pads. The high temperature of brake pads may lead to brake fade. These holes allow the air to pass through the disc. The flowing air increases the rate of heat transfer from the disc and helps in keeping it cooler.

Disc of car, having air  vents

On other hands the car discs do not have holes in them. This is because they are provided with some air vents through out their cross section. These vent have pump like curved channels which sucks the air at their center and supply it outwards .This helps in uniform cooling of the whole disc surface.

During driving in wet condition the disc may also get wet. This will decrease the grip of brake pads on the disc. The holes provided on the disc surface also help in removal of water from the surface. During brake operation the water on the disc get heated up and converted to steam . These holes provide a passage for the steam to get removed.

Brake fade

Brake fade is a phenomenon which decreases the braking efficiency. It causes the braking power to reduce and you feel that the brakes are not being applied with the force they were being applied at the time of starting. This occurs due to heating of brake pads. The heated brake pads emit some gaseous substances which cover the area between the disc and the brake pads. These gases disturb the contact between the brake pads and the disc and hence decreases the braking efficiency.