Rolling bearing unit for wheel

A rolling bearing unit for a wheel, comprising:

• an outer ring member that includes a flange portion which is formed on an outer periphery of the outer ring member and which is fitted to a vehicle body-side member;
• an inner ring member that is rotatably fitted in the outer ring member;
• and
• double-row rolling elements that are arranged between the outer ring member and the inner ring member such that the rolling elements are able to roll between the outer ring member and the inner ring member,
• wherein the flange portion includes a first flange portion and a second flange portion that are formed on an upper-side portion of the outer periphery of the outer ring member, and a third flange portion and a fourth flange portion that are formed on a lower-side portion of the outer periphery of the outer ring member,
• wherein each of the first flange portion, the second flange portion, the third flange portion and the fourth flange portion includes a bolt-hole that is used to fit the outer ring member to the vehicle body-side member,
• wherein the first flange portion is symmetrical to the second flange portion with respect to a vertical line that passes through a rotational center of the outer ring member, and the third flange portion is symmetrical to the fourth flange portion with respect to the vertical line that passes through the rotational center of the outer ring member, and
• wherein a first angle that is formed between a line that connects a center of the bolt-hole of the first flange portion to the rotational center of the outer ring member and a line that connects a center of the bolt-hole of the second flange portion to the rotational center of the outer ring member differs from a second angle that is formed between a line that connects a center of the bolt-hole of the third flange portion to the rotational center of the outer ring member and a line that connects a center of the bolt-hole of the fourth flange portion to the rotational center of the outer ring member, and
• wherein the second angle comprises a value less than a value of the first angle so as to enhance a rigidity of the outer ring when the flange portion is fitted to the vehicle body-side member.