A bearing unit comprises a radially outer stationary race (1) and a pair of radially inner rotatable half-races (2a, 2b). Au intermediate annular chamber (8) is defined between the outer race (1) and the inner half-races (2a, 2b) The intermediate chamber communicates with the outside through first air passages (5) formed in the outer race (1) and with the inside of the bearing unit through second radial air passages (6) defined between the inner half-races (2a, 2b). An intermediate annular member (10) is axially interposed between the inner half-races (2a, 2b) and defines the second passages (6).