Spirally winding a belt reinforcing layer for a pneumatic radial tire at a higher density beneath the groove areas

A process for the production of a pneumatic radial tire, including the step of forming an unvulcanized tire which comprises at least two belt layers disposed on the outer periphery of a carcass, a belt reinforcing structure including at least one belt reinforcing layer comprising an organic fiber cord and disposed on an outer peripheral portion of at least a shoulder region of an outermost one of the at least two belt layers and extended at least part way across said at least two belt layers, and an unvulcanized tread rubber disposed on the outer periphery of the belt reinforcing structure;

• and the step of molding the unvulcanized tire by a mold having main groove-forming ribs for forming on the outer surface of the tread rubber at least two main grooves extending in the circumferential direction of the tire;
• wherein the belt reinforcing layer constituting the belt reinforcing structure is formed by spirally continuously winding a single organic fiber cord in a manner such that before the molding of the unvulcanized tire, the belt reinforcing layer has a greater density of winding of the organic fiber cord in its regions located inner to the main groove-forming ribs than in its remaining region, whereby after the molding of the unvulcanized tire, the cord density in its regions inner to the main groove-forming ribs is set to lie within a range of 90 to 110% of the cord density in its remaining region.