A cap assembly for a wheel including a cup-shaped cap member having a plurality of annular ridges disposed around a circumference thereof, and a retainer ring having a plurality of axially extending flange portions disposed around a circumference thereof. The retainer ring is slidably coupled to the cup-shaped member, the axially extending flange portions are angled relative to a position normal to the ring, and the plurality of axially extending flange portions correspond to the plurality of annular ridges. When the cap assembly is inserted into the wheel, the retainer ring slides along the cup-shaped member and the annular ridges force the axially extending flange portions to the position normal to the ring to attach the flange portions to the wheel.