In one representative embodiment, a tire comprises an inner shell having a hollow interior space, an outer shell disposed radially outward from the inner shell, and at least one pump assembly disposed adjacent to the inner shell and having a compressible tube portion, wherein the tube portion of the pump assembly is configured to expand radially outwardly beyond the outer shell and to compress radially inwardly, and wherein the pump assembly is configured to direct a fluid from the tube portion of the pump assembly to the interior space of the inner shell.