In a wheel supporting rolling bearing unit, an inner end opening out of both end openings of a space in which balls 14, 14 are provided is sealed with a cap 17a. An outer end opening is sealed with a seal ring 16c having 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 running resistance of the seal ring 16c based on a friction between the seal ring and a counter surface is regulated in a range of 0.03 to 0.2 Nm.