Do not buy non disc brakes? What is the difference between disc brakes and drum brakes?

Author: Automotive Observer

Link: https://zhuanlan.zhihu.com/p/101240547

Source: Zhihu

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There are many types of brakes for cars, and currently the most common ones are drum brakes and disc brakes. I don't know if you have noticed, drum brakes are generally used on trucks, while disc brakes are mostly used on passenger cars such as sedans and SUVs. Why is this? And disc brakes are also divided into ordinary disc brakes, ventilated disc brakes, and lined ventilated disc brakes. Although they are all disc brakes, the prices vary greatly. What is the difference between these? Freight trucks love drum brakes the most, while small cars prefer disc brakes. First, let's take a look at the difference between drum brakes and disc brakes. Literally, drum brakes rely on "drum" brakes, while disc brakes rely on "disc" brakes. Drum brakes use brake pads that are stationary inside the brake drum to remove friction from the drum that rotates with the wheels, in order to generate friction and reduce the wheel speed. Simply put, brake pads are usually stationary inside the brake drum. When braking is needed, the brake pads are pushed by the piston onto the brake drum, causing friction and resistance. Disc brake is achieved by clamping a fixed caliper to generate frictional resistance with the rotating disc of the wheel, achieving braking effect. For an easy to understand example, when we play with a turntable, we use a "caliper" made up of our thumb and other four fingers to prevent the turntable from rotating. Is this easy to understand? Compared with ordinary disc brakes, drum brakes have a larger contact area between the friction shoes and brake drums, resulting in greater frictional resistance during braking. Moreover, as long as you give it an initial braking force, drum brakes will automatically brake tighter and tighter. This is because as the brake drum rotates, the brake pads will slowly be wrapped around the brake drum by friction, and the tighter the winding, the greater the braking force. Therefore, drum brakes are generally used in freight vehicles. In addition, drum brakes have the advantages of relatively simple parts processing and composition, and relatively low manufacturing costs. Of course, drum brakes also have drawbacks. The structure of drum brakes is relatively sealed, and their heat dissipation is not as good as that of disc brakes. During continuous braking, the brake drum will expand due to heat, causing an increase in the stroke when the brake pedal is pressed, and the braking response is not as expected, which is commonly known as thermal attenuation. Due to being directly exposed to the air, the heat generated by the disc brake will be carried away by the flow of air, which means it has an inherent "air cooling" effect. When continuously stepping on the brake, it is not easy to cause brake thermal decay and brake failure. Moreover, disc brakes have better drainage, which can reduce the occurrence of poor braking caused by water or mud. In addition, compared to drum brakes, disc brakes have a simple structure and are easy to maintain. But his disadvantage is that there is no automatic braking effect of drum brakes, which makes the braking force of disc brakes lower than that of drum brakes. Moreover, the friction area between the brake pads and brake discs of disc brakes is smaller than that of drum brakes, so the frictional resistance generated by brakes is not as large as that of drum brakes. Disc brakes are generally used on lightweight small cars. Some high-performance sports cars intentionally increase the area of the brake disc and also increase the number of pistons in the caliper to increase the braking force in order to improve the braking force of the disc brake. Just like if you want the turntable to stop quickly, you have to use greater force to "pinch" it. In this way, it also brings about problems such as higher brake heat and obvious brake heat decay, and at this time, ventilated disc brakes are applied. Ventilation disc brakes have better cooling effects and are more expensive. Ventilation disc brakes have a ventilation device on the brake disc, which is a "honeycomb" between two discs leading to the center of the disc. When the disc rotates with the wheels, the air flow outside the disc is fast and the pressure is low, while the heat inside the disc is exported from the high-pressure area of the "honeycomb" to the low-pressure area outside the disc due to the higher brake temperature and pressure inside the disc, which plays a role in cooling the brake system. Some brake discs have evenly distributed small holes, which is also for faster heat dissipation of the brake discs. The lined and perforated brake discs are actually arranged with some concave lines on the brake discs, which can further improve the heat dissipation of the brake discs. This type of lined and perforated brake disc is more expensive and is generally common in luxury cars. Finally, some people said that if they drill some holes on ordinary brake discs, can they also achieve the purpose of heat dissipation? In principle, it is possible, but uneven distribution of holes can disrupt the dynamic balance of the brake disc during high-speed rotation, which can easily cause brake damage and failure. In addition, the original stiffness and durability of the brake disc will also be greatly reduced. To achieve better brake performance, it is best to go to a professional modification shop to replace it with a more advanced brake kit. This article is original by an automotive observer, and any plagiarism will be held legally responsible.