A circular tire rim has intermediate its ends an annular drop-center section, and coaxially on opposite ends thereof enlarged diameter, circumferential flange sections engageable with the beads of a tubeless tire to support the tire on the rim. Adjacent one end thereof the drop-center section has projecting from its outer peripheral surface a pair of projections angularly spaced 180° from each other about the axis of the rim. Removably secured coaxially on the drop-center section of the rim is an annular runflat device the outer peripheral surface of which normally is radially spaced from the inner peripheral surface of the properly inflated tire on the rim, but engageable by and slidably supporting the inner peripheral surface of the tire when the latter is operated in a runflat mode. The two projections on the drop-center section of the rim seat in registering recesses formed in the inner peripheral surface of the runflat device to prevent any relative movement between the device and the rim.