This modification involves the installation of an additional set of calipers and rotors on the rear wheels of the BMW E46 chassis. Typically, this setup is implemented to enhance braking performance, primarily for applications such as drifting or rallying where independent control of the rear brakes is advantageous. The supplemental calipers are often hydraulically actuated, providing the driver with the ability to lock the rear wheels independently of the main braking system.
The practice of adding a separate braking system for the rear wheels offers several benefits. It allows for precise control during maneuvers requiring controlled rear wheel lock-up, improving vehicle handling in specific motorsports disciplines. Historically, this modification arose from the need for more responsive and reliable handbrake systems in competitive driving, evolving from simpler mechanical solutions to more sophisticated hydraulic arrangements that offer greater adjustability and force.
