A unitary, essentially cylindrical, rigid closed ring member is provided for use with pneumatic tires having spaced mounting beads at the inner diameter for engagement with edge flanges of a circumferentially divided two-part wheel rim, the wheel rim providing an essentially flat central bearing surface joining the flanges in bead receiving portions which may be angled 5.degree. or 15.degree. from the horizontal; the ring member having an outside diameter approximately 5/8" greater than the inside diameter of the tire beads, an edge thickness of about 1/4" for engagement with inner surfaces of the tire beads, and a width such as to firmly support the tire beads in engagement with the rim flanges when the wheel is fully assembled, the central portion of the ring having a smooth inner surface for close engagement with the bearing surface of the wheel, and the outer surface of the ring having a central annular depression track about 1/4" deep, and of a width to freely and rotatably receive a run-flat support ring comprising a plurality of arcuate members assembled in end-to-end relation.