There are brake rotor, brake drum and brake air. Older cars have front and rear drums. Many cars have brake rotor both front and rear. Because brake rotor have better heat dissipation than brake drum, they are not prone to thermal degradation under high-speed braking, so their high-speed braking effect is good. But at low speed cold brake, the braking effect is not as good as brake drum. The price is more expensive than the brake drum. Therefore, many mid-to-high-end cars use full-disc brakes, while ordinary cars use front and rear drums, and relatively low-speed trucks and buses that require large braking power still use brake drum.