Radial-ply tire having low rolling resistance

Claim 1

A radial-ply tire having: at least one carcass ply consisting of a plurality of cords arranged at an inclination angle of 70° to 90° to the equator plane of the tire, said carcass ply being retained at its both ends by means of bead wires; a belt layer for reinforcing the portion of said carcass ply behind the tread, said belt layer being disposed between the tread and the carcass ply; an undertread layer disposed at the outside of said belt layer; an inner liner layer disposed at the innermost portion of the tire; and an outer liner layer disposed adjacent to the outer surface of said inner liner layer; wherein the improvement comprises that the rubber portion of at least one of said carcass ply and said undertread has a visco-elastic property of loss tangent, tan δ, of 0.2 or lower (tan δ≦0.2) and storage modulus, G, of 120 kg/cm 2 or higher (G≧120 kg/cm 2 ) measured by a shearing vibration at a frequency of 50 H z and a dynamic strain of 5% under a temperature of 40° C. and is a rubber which is formed by adding 2.50 to 3.50 weight parts of sulfur, 1 to 2 parts of vulcanization accelerator of sulfenamide group and 40 to 65 weight parts of carbon black having a mean particle size of 25 to 77 mμ to 100 weight parts of at least one vulcanizable rubber which is selected from the group consisting of natural rubber, diene rubber and diene copolymer rubber.