Abstract: A disc brake rotor (10; 50) provides two oppositely-facing annular friction surfaces (20, 22). The rotor (10; 50) comprises a first portion (16) which provides one of said annular surfaces (20), and a second portion (18) which provides the other of said annular surfaces (22). The first and second portions (16, 18) ar arranged in spaced parallel relationship and are joined by vanes (32) between which are defined cooling ducts (34). The ducts (34) extend radially of the rotor (10; 50) and are arranged so that, as the rotor (10; 50) is rotated, air passes through the ducts (34) and acts to cool the rotor (10; 50). In order to increase cooling efficiency, the transverse cross-sectional area of each duct (34) decreases progressively between an inlet (36) to the duct (34) and an intermediate region (40) thereof and increases between said intermediate region and an outlet (38) of the duct (34).