Abstract: A substantially flat plate is positioned on a rim, which has a large central opening and no lug holes, to enable a tire to be mounted thereon or dismounted therefrom by a tire changer requiring a rim to have lug holes around the central opening to hold the rim. The flat plate has its length selected so that its opposite ends rest on an annular portion of the rim. The opposite ends of the flat plate have substantially the same curve as the annular portion of the rim on which they rest. The flat plate has a central circular opening to receive a threaded shaft of the tire changer supporting the rim. A hollow tube extends downwardly from the bottom surface of the flat plate adjacent the central opening for disposition over a positioning pin of the tire changer on which the rim is supported.