Hub unit with rotation speed sensor

A hub unit with a rotation speed sensor (35) is described comprising a stationary outer ring member (9) having an outer raceway (8) formed thereon, a rotatable hub (3) having an axially inner end with a male thread portion formed thereon, an inner ring member (4) having an inner raceway (2b) formed thereon, and fittingly fixed onto the hub (3), a nut (6) screwed on the male thread portion of the hub (3) to axially retain the inner ring (4), a plurality of rolling members (10) located between the outer raceway (8) and the inner raceway (2), a cover (34) fittingly fixed to the outer ring member (9) at its opening end portion, an annular sensor (35) supported by the cover (34) so as to be located radially between the nut (6) and the cover (34), a rotatable tone wheel (29) made of magnetic material and fittingly fixed onto the inner ring (4), the sensor (35) comprising an annular permanent magnet (36), a magnetic stator (37) and a coil (38), so that the sensor (35) is opposed generally circumferentially to part of the tone wheel (29) with a small clearance therebetween.