Patent ID: 8225835

Claim:
A pneumatic radial tire including: at least two cross belt layers disposed on an outer circumferential side of a carcass layer in a tread portion; and at least one circumferential-direction reinforcement layer disposed between these cross belt layers, a width of the circumferential-direction reinforcement layer being smaller than that of each cross belt layer, the pneumatic radial tire wherein, the cross belt layers are separated away from each other at outer sides respectively of end positions, in a width direction, of the circumferential-direction reinforcement layer, the circumferential-direction reinforcement layer includes steel cords of two types which differ in elongation at break, and the steel cord having relatively small elongation at break is disposed in a center portion of the circumferential-direction reinforcement layer, whereas the steel cord having relatively large elongation at break is disposed in each of outer side portions of the circumferential-direction reinforcement layer, wherein the steel cord disposed in the center portion of the circumferential-direction reinforcement layer has an m×n structure in which a direction of a first twist of filaments of the steel cord coincides with a direction of a second twist of the filaments, the steel cord having elongation at break of not less than 3%, and the steel cord disposed in each of the outer side portions of the circumferential-direction reinforcement layer has filaments which are preformed into a zigzag shape, the steel cord having elongation at break of not less than 6%.