A wheel assembly including a rigid wheel having a radially outer rim wall presenting a polygonal shape with a plurality of outermost vertices connecting a plurality of planar faces, and a flexible tire mounted on the outer rim wall. The planar faces of the rigid wheel each have a spacer positioned thereon. The tire is supported by the vertices of the rim wall and is separated from the rim faces by a space, portions of the tire located between the vertices being configured to flex inwardly when subject to ground engaging pressure, the spacers configured to limit the amount of inward flex of the portions of the tire between the vertices.