Why do cars have front disc and rear drum brakes?
2 Answers
This is mainly due to the consistency and stability of braking performance. Below is the relevant information: 1. Consistency of braking performance: Drum brakes have greater braking performance, while disc brakes have higher stability in braking performance. The consistency of braking performance mainly refers to the degree to which braking performance is maintained. This involves the issue of thermal fade, as general brake drums or discs are made of cast iron, and the friction pads are made of several materials such as semi-metallic and asbestos-free. During normal braking, the temperature of the friction pads is generally around 200 degrees. When braking frequently, the temperature of the friction pads will rise, causing the friction coefficient of the friction pads to decrease, meaning the braking performance will decline. This is the so-called thermal fade phenomenon. 2. Stability of braking performance: When the friction coefficient of the friction pads decreases due to rising temperatures, the intelligent performance factor of various types of brakes will also decrease. The most affected here is the servo type, followed by duo-servo, leading-trailing, and disc. Therefore, the least affected is the disc brake, making the stability of disc brake performance the best.
The use of disc brakes on the front wheels and drum brakes on the rear wheels is primarily due to differences in braking force distribution and heat dissipation requirements. Having driven many cars and researched numerous models, I've found that during hard braking, the front wheels bear over 70% of the braking force, generating significant heat. Disc brakes dissipate heat quickly through exposed brake pads and ventilation designs, preventing brake fade and ensuring safety. Rear wheels require less braking force, and drum brakes offer lower costs along with better dust protection and sealing, making them suitable for long-term durability. This design allows manufacturers to save on production costs, benefiting especially economy family cars. Additionally, all-disc brakes are common in high-end vehicles, but entry-level cars often opt for front disc and rear drum configurations to balance performance and maintenance. For instance, disc brakes make pad replacement easier during maintenance, while rear drum brakes experience fewer issues. Overall, this configuration enhances reliability and is well-suited for everyday driving.
