An outer rim molded material is molded by forging or casting, a portion of the outer rim which extends from a hump to a bead seat is separated from part of a rim flange precursor 2a and is caused to fall in a sloping fashion inwards of a wheel width so as to form a bead seat precursor 12a, and the bead seat precursor 12a so formed is then joined to be welded to a top or side of a rim well rising portion precursor 5b. An external surface is cut to be finished to a proper shape, and an annular hollow portion 8 is formed underneath a lower surface of the bead seat portion.