Abstract: A disc brake of a two-wheeled vehicle comprises two friction pads which press against either side of a disc rotating along with the wheel of the vehicle in motion. The friction pads are provided with a friction surface. The disc is provided in the surface of both sides thereof with a plurality of first arrest surfaces, second arrest surfaces, and recesses, which are all exerted on sequentially by a stress brought about by the friction surface of the friction pads at the time when the friction pads press on the disc.

Abstract: A bicycle wheel rim is composed of a friction surface extending along the rim. The friction surface is provided with a plurality of action units each having a primary action area and a secondary action area and a secondary action area. The primary action area has a flat surface capable of frictional engagement with the brake shoes of a bicycle brake system. The secondary action area has a concave surface capable of frictional engagement with the brake shoes of the bicycle brake system. The action units of the bicycle wheel rim are thus capable of cooperating with the brake shoes to bring about a smooth and stable braking action for slowing or stopping the bicycle wheel in motion.