A radially outer stationary bearing race (11) defines, on one if its sides, an inner cylindrical surface (29) and a radial side surface (32). A radially inner bearing race (15) has an outer cylindrical surface (26) facing the inner cylindrical surface (29). A magnetic encoder (23) in form of an annular disc is fixed onto the outer cylindrical surface (26) of the inner race (15) and is protected by a cover of non-ferromagnetic material (30) mounted on the outer race (11) and abutting against the radial side surface (32). The encoder (23)extends radially from the outer cylindrical surface (26) of the inner race (15) up to near the inner cylindrical surface (29) of the outer race (11). No sealing device is mounted in the gap between the cylindrical surfaces (29) and (26).