Tread reinforcing construction of pneumatic radial tire for heavy-load vehicles

Claim 1

A tread reinforcing construction of a pneumatic radial tire, comprising a rubberized carcass ply composed of cords embedded therein and arranged substantially parallel with the radial direction of the tire, a rubberized belt superimposed about said rubberized carcass ply and arranged at a crown portion of the tire, said rubberized belt being composed of a plurality of metal cord plies each formed of conventional steel cords embedded therein and having a high rigidity in the circumferential direction, the width of said belt being greater than the width of the center portion of said tread portion, and at least one additional rubberized reinforcing layer interposed between said belt and a tread rubber portion, said reinforcing layer composed of a reinforcing element embedded therein and formed of a bundle of at least two helically formed filaments assembled together without twisting at random, said reinforcing element having a cord angle of between 10 degrees and 75 degrees, each of said helically formed filaments being made of steel, said reinforcing element having an elongation at tensile breaking strength which is at least 1.2 times larger than the smallest elongation at breaking strength of the metal cord plies constituting a main layer of said belt, and said additional reinforcing layer as a whole having a rigidity in the circumferential direction which is smaller than that of said belt.