Drum vs. Disk Brakes
Besides the engine, which makes the car go, the most important component of an automobile is its brakes. The brakes are what makes your car ...
Besides the engine, which makes the car go, the most important component of an automobile is its brakes. The brakes are what makes your car stop and are a vital aspect in the everyday operation of the vehicle. Just like other automobile components, brake technology has evolved over the years. Early cars used drum brakes on all four wheels to stop the vehicle. Drum brakes have since been replaced by more efficient disk brakes, but drum brakes can still be found on the rear wheels of some cars.
Design
A drum disc consists of three components: the backing plate, the brake shoes and the brake drum. The backing plate connects the brake system to the axle of the vehicle and holds the brake shoes in place. The brake drum is then placed on top of the backing plate, with the brake shoes inside. A disk brake also has three components and works similarly. There is the brake disc, which connects to the wheel and axle; the brake pads; and the calipers, which hold the brake pads.
Function
Both brake systems work on the basis of friction to stop the vehicle. When brake force is applied to a drum brake, the brake shoes apply friction to the brake drum, slowing down the vehicle. When brake force is applied to a disk brake, the calipers clamp closed, applying the brake pads to the rotor to slow the vehicle down.
Heat
Where these two systems differ is how they handle heat. The drum brake is an internal system, with the brake pads being held inside of the brake drum. As such, it is easy for heat to build up inside the unit. When heat builds up, the brakes fade and loose their stopping power. Disk brakes, on the other hand, are more exposed. This allows for the brake disc and pads to cool much easier and for the brakes to hold their stopping power.
Stopping Power
All things being equal, disk brakes do not provide significantly better stopping power in dry conditions than drum brakes. Up to 70 percent of a vehicle's stopping power goes to the front wheels, so a car with drums in the rear will not vary greatly from a car with disks in the rear. They do have the advantage when it comes to heat build up, so high performance cars will rely exclusively on disk brakes. Another area where disk brakes have an advantage is in wet weather.
Cost
The main reason that drum brakes are still in use is because of cost. They are much cheaper to manufacture than disk brakes. Also, drum brakes can double as a parking break, further reducing the cost of production of a vehicle. With disk brakes on all four wheels, manufacturers have to build a separate parking brake in the brake rotor, adding to its cost.
