What Causes Brake Noise When the Car is Cold?

[Roy]

Cold-start brake noise occurs due to the following reasons: 1. In principle, braking involves friction between two components that converts mechanical energy into thermal energy. During this process, intense friction generates severe vibrations. When the vibration frequency matches or approaches the natural frequency of the brake pads (or related components), resonance occurs, leading to abnormal noises or squealing. This is particularly noticeable when descending garage ramps. 2. Braking systems are typically divided into disc brakes and drum brakes, with disc brakes being more prone to these abnormal noises/squeals. 3. Drum brakes: Due to their larger size and heavier weight, their natural frequency is lower. Low-frequency resonance from outside the vehicle often fails to transmit sound into the cabin, making occurrences rare. 4. Disc brakes: Their smaller size, lighter weight, and higher natural frequency make them susceptible to high-frequency resonance, resulting in abnormal noises/squeals. Resonance can occur across various components—brake discs, brake pads, calipers, etc. The piercing squeals heard are usually emitted by the resonance of the brake discs.