In a wheel supporting rolling bearing unit, both end openings of a space in which balls 14, 14 are provided are sealed with seal rings 16c, 16d each having two to three seal lips. A rolling resistance that changes based on a preload is regulated in a range of 0.15 to 0.45 Nm, and a total running resistance of both seal rings 16c, 16d based on a friction between the seal lips and counter surfaces is regulated in a range of 0.06 to 0.4 Nm.