Rolling bearing unit with rotational speed sensor

A rolling bearing unit with a rotational speed sensor comprising a stationary outer ring having a first raceway, a rotatable inner ring having a second raceway, a plurality of rolling elements rotatably provided between the first and second raceways, an encoder having circumferentially changing magnetic characteristics and connected to the rotatable ring, the inner ring having a stepped portion defining a cylindrical mounting surface for the encoder with smaller diameter than a shoulder section of said inner ring. The inner ring may be fixed to the hub by crimping an axially inner end of the hub outward.