What is the difference between disc brakes and drum brakes? The main difference between disc brakes and drum brakes is their size and their position on the wheel. They both have advantages and disadvantages.
All cars obviously have brakes, and they work on a hydraulic system. The brake lines are filled with a brake fluid that is a mix of glycol-ether (a type of solvent) and additives to stop the brake lines from corroding or sticking. When you push down on the brake pedal, the brake fluid moves because the liquid doesn’t compress, and pushes the brakes down onto the wheel. You don’t have to push hard because a hydraulic line will increase the force you put on the brake pedal by a factor of ten. The brake is made of metal with a friction pad that presses on the wheel and stops the wheel from spinning. The harder you press on the brakes, the more firmly the brakes press on the wheel rim, and the faster the car stops. Hydraulic brakes work for cars because they are not that heavy, but they would not be able to stop a truck or a bus. Larger vehicles use air brakes. It is a similar idea, but they use compressed air rather than brake fluid to trigger the brakes. Power from the engine is used to compress air, which is stored in a tank. When the driver wants to stop, they press the brake pedal and the compressed air goes into the brake lines, forcing the brakes against the wheel. When you release the brakes, the air is released, which is why you hear a hissing sound when a large vehicle stops. Air brakes have greater stopping power than hydraulic brakes, and they also have a fail-safe because if air pressure is lost, the brakes automatically lock.
So, the main difference between disc brakes and drum brakes is their size and their position on the wheel. Drum brakes operate on a drum connected to the inside of the wheel. There are two drum brakes on each wheel, called brake shoes, and they are curved to fit the drum. Each one is a little smaller than a quarter of the size of the drum. The friction pads are on the inside of the brake shoe, and when you press on the brakes, the two brake shoes press down on the drum, and the friction stops the drum spinning, stopping the car. Disc brakes work on a disc that is attached to the wheel, a couple of centimeters thick. The brake is housed in a caliper through which the disc passes through. There are two brake pads in the caliper, and when the brake pedal is pressed, one brake pad is pushed onto the disc and the other brake pad is pulled onto the disc. The two brake pads squeeze the disc, and the friction stops the wheel spinning.
So, which is better, drum brakes or disc brakes? They both have advantages and disadvantages. Drum brakes are much cheaper to manufacture than disc brakes, and this is the main reason why the majority of cars have drum brakes. Drum brakes also last a lot longer than disc brakes. This is because the disc brakes have to apply a lot more force to the disc to stop the wheel, and that means they wear out much more quickly. Drum brakes get a lot hotter than disc brakes because they are larger and can’t lose their heat fast enough. Disc brakes can pass the heat from the braking friction into the disc, which is very large and cools down faster. However, because they apply more force, disc brakes can stop a car more quickly than drum brakes can. Drum brakes are easier to get to and easier to maintain as well. To get to disc brakes, you need to take the caliper apart. Also, interestingly, disc brakes are not very good as parking brakes because they contract when they are cold. When you stop, you have to brake, and the brakes heat up, expanding into the wheel disc. After you have parked for a while, they cool down, contract, and pull away from the disc, allowing the car to roll. A lot of sports cars with disc brakes also have a parking drum brake.
If you have the money for them and you are using a high-performance sports car, you want disc brakes because they are more responsive and more effective at high speed. If you are driving an expensive sports car, then you probably don’t mind the price and the difficulty in maintaining disc brakes. If you are just driving a regular car, then drum brakes are the way to go. Just make sure they have ABS and, if you are driving a hybrid or an electric car, regenerative braking. And this is what I learned today.
Sources
https://www.precisiondieselca.com/how-air-brakes-work-in-big-trucks
https://en.wikipedia.org/wiki/Brake_fluid
Photo by Vincenzo Malagoli: https://www.pexels.com/photo/close-up-photo-of-ferrari-rim-2922140/