A bicycle disc brake is a high-performance braking system. Based on the actuation medium, it can be classified into mechanical disc brakes (cable-actuated) and hydraulic disc brakes (fluid-actuated). Hydraulic systems are further divided into open systems (with reserved space for fluid expansion) and closed systems (with isolated hydraulic circuits). Brake pads are available in different materials, including organic pads (heat-resistant) and metallic pads (wear-resistant), and must be compatible with either mineral oil or DOT-standard brake fluid. Disc brakes are widely used on modern mountain bikes, road bikes, and some urban bicycles. Compared with traditional rim brakes, they offer significant advantages in braking performance, stability, and overall safety.