What are the differences between drum brakes and disc brakes?
4 Answers
The differences between drum brakes and disc brakes lie in braking force, heat dissipation performance, drainage function, structure, and cooling effect. Braking refers to stopping a moving vehicle, and the brake is a component in the braking system that generates resistance to the vehicle's movement. Currently, friction brakes are commonly used in vehicles, which utilize the friction between fixed and rotating components to produce braking torque. These brakes are further divided into disc brakes and drum brakes. The specific differences are as follows: Different braking force: In terms of braking force, drum brakes provide significantly stronger braking force than disc brakes. This is not because drum brake technology is more advanced but due to their inherent structural characteristics. In a drum brake system, there is a drum-shaped metal component, which is the core part of the drum brake, hence the name. Different heat dissipation performance: Drum brakes operate in a confined space, resulting in poor heat dissipation. During braking, a large amount of heat accumulates, causing the brake shoes and drum to deform under high temperatures, leading to brake fade and vibration, which reduces braking efficiency. Different drainage function: Drainage is another advantage of disc brakes over drum brakes. When water enters the braking system, its impact on braking performance is evident. If the water cannot be drained promptly, braking performance will significantly decline. The enclosed design of drum brakes is clearly less effective for drainage compared to disc brakes. Different structure: Disc brakes have a compact and simple structure, while drum brakes are relatively more complex. However, drum brakes achieve the same braking force with a much smaller diameter than disc brakes. Different cooling effect: Disc brakes have exposed brake shoes, resulting in better heat dissipation and more stable braking performance. In contrast, drum brakes have brake shoes enclosed within the drum, making heat dissipation difficult. Prolonged braking causes the braking force to diminish as heat increases. Principle of drum brakes: Inside the brake drum, hydraulic pressure acts on the pistons of the brake wheel cylinder, pushing the curved brake shoes outward. Alternatively, friction material attached to the brake shoes presses against the inner surface of the drum, slowing the rotation of the drum and axle to achieve braking. Working principle of disc brakes: Hydraulic oil pushes the brake pads against the brake disc through cylinders, generating friction to brake. Disc brakes installed on high-speed shafts come in two torque specifications: 10,000 N·m and 12,500 N·m. The brake disc diameter is 800 mm. Each brake set has four cylinders controlled by a hydraulic system. The features include high braking torque, excellent heat dissipation, adjustable oil pressure, and stepless variation of braking torque during operation.
The difference between drum brakes and disc brakes is quite significant. Let's start with drum brakes, which are like a large drum installed inside the wheel hub. When you press the brake, hydraulic pressure pushes the brake shoes outward to rub against the inner drum wall, creating friction to stop the vehicle. The advantages are strong braking force and low cost, which is why older cars and trucks often use them on the rear wheels. The downsides include poor heat dissipation—frequent braking on downhill slopes can easily lead to overheating and failure—and rain or mud getting inside can affect braking performance. Disc brakes, on the other hand, have the brake rotor exposed and directly connected to the caliper, which clamps the brake pads when braking. They excel in heat dissipation, provide stable braking even during emergency stops, and aren’t affected by rain or water. Nowadays, most cars priced above 100,000 yuan are equipped with disc brakes, significantly improving driving safety.
Having driven for twenty years, the switch from drum brakes to disc brakes was particularly noticeable. Drum brakes have a simple structure and cheap parts, making them a favorite for mechanics to tinker with. However, prolonged driving quickly reveals their shortcomings—during traffic jams, the pedal feel becomes softer, and the braking distance noticeably increases. Disc brakes, though more expensive, feature cooling fins that dissipate heat quickly, eliminating concerns about heat fade when driving on mountain roads in summer. If you're upgrading the braking system, pairing disc brakes with ventilated rotors delivers immediate results. Nowadays, the two braking methods are often used in combination; it's quite common for family cars to have disc brakes in the front and drum brakes in the rear, balancing cost savings with safety.
The key differences between drum brakes and disc brakes lie in their structural performance. Drum brakes' enclosed design delivers strong braking force, but dissipates heat as slowly as a slow cooker - at high temperatures, the friction coefficient of brake shoes plummets by one-third. Disc brakes' open structure allows rapid heat dissipation and far superior water drainage in wet conditions. From a maintenance perspective, replacing drum brake shoes requires wheel and drum disassembly, taking over 30 minutes; disc brakes allow pad replacement by simply removing the wheel, a 10-minute job. However, drum brakes' self-adjusting mechanism proves more reliable under heavy loads, which is why truck rear wheels still use them. For car enthusiasts choosing between the two, disc brakes are the obvious choice - the performance gap is simply too significant.
