Abstract: A mechanical power brake assembly for the rear wheel of a bicycle that magnifies the manual force applied to asymmetric brake shoes so as to induce a greater force through the hand lever, cable and brake arms. The force applied to the brake pad gripping surface induces a greater force by harnessing the forward momentum of the bicycle. An increase in the forward momentum of the bicycle results in a greater magnification of the force to the brake shoe. In one embodiment of the brake assembly, each brake shoe is configured to pivot on a connecting rod. In another embodiment of the brake assembly, the brake shoes are secured with a saddle that pivots within each brake arm configured as a cantilever. An embodiment of the asymmetric brake shoe may be mounted on any existing brake arms without requiring a proprietary brake arm assembly.