A segmented annular mold for forming a tread belt having a reinforcing belt structure, the belt structure having a radial thickness (t) is disclosed. The mold has a plurality of radially movable and outwardly expandable inner segments for forming the inner surface of the tread belt and a plurality of radially movable and contracting outer segments for forming the outer tread belt surface. The radially inner and radially outer segments form a mold parting line at a location radially outward of a midpoint of the belt reinforcing structure of the tread belt at a location greater than 50% (t) as measured from the radially innermost surface of the belt reinforcing structure. The radially inner segments have upper and lower lateral edge forming portions extending outwardly to the parting line. Similarly, the radially outer mold segments have upper and lower lateral edge forming portions extending inwardly to the parting line. The parting line is located at least radially outwardly of a radially inner second belt layer of the belt reinforcing structure.