A tire/wheel assembly in which a run-flat support member 3 is inserted into a cavity of a pneumatic tire 2, the run-flat support member 3 including a circular shell 4 in which the outer circumferential side thereof is used as a support surface and the inner circumferential side thereof is opened to have two leg portions, and elastic rings 5 supporting the ends of the two leg portions on a rim. The outer circumferential surface of the circular shell 4 in a cross-section cut in a tire width direction has a shape with a plurality of convex portions 4a, 4b, aligned in a tire width direction, and these convex portions have a plurality of different kinds of radius of curvatures and/or thickness.