Pneumatic radial tires with circumferential cord belt layer having specified cord twisting structure

A pneumatic radial tire comprising a carcass toroidally extending between at least a pair of bead cores and a belt superimposed on a crown portion of the carcass and comprised of a single slant belt layer containing a plurality of cords or filaments arranged at a given inclination angle with respect to an equatorial plane of the tire and at least one circumferential belt layer laminated on the slant belt layer and containing a plurality of cords arranged substantially in parallel to the equatorial plane, wherein each cord used in the at least one circumferential belt layer is made from vinylon fiber and has a layer twisting structure and a total denier DT of 1000 d-6000 d and a twist constant Nt=T×(0.139×DT/2≦1/ρ)½×10−3≦0.6 wherein T is a twisting number (twist turns/10 cm) and ρ is a specific gravity, wherein a gauge (t1) of rubber located between the cords of the slant belt layer and the cords of an innermost circumferential belt layer in a radial direction of the tire is made larger in side end regions of the tire than in a central region thereof in the widthwise direction at a radial section of the tire, and a width (L2) of the central region is 50-90% of a width (L1) of the slant belt layer centering around the equatorial plane.

A pneumatic radial tire comprising a carcass toroidally extending between at least a pair of bead cores and a belt superimposed on a crown portion of the carcass and comprised of a single slant belt layer containing a plurality of cords or filaments arranged at a given inclination angle with respect to an equatorial plane of the tire and at least one circumferential belt layer laminated on the slant belt layer and containing a plurality of cords arranged substantially in parallel to the equatorial plane, wherein each cord used in the at least one circumferential belt layer is made from vinylon fiber and has a layer twisting structure and a total denier DT of 1000 d-6000 d and a twist constant Nt=T×(0.139×DT/2×1/ρ)½×10−3≦0.6 wherein T is a twisting number (twist turns/10 cm) and ρ is a specific gravity, wherein a gauge (t2) of rubber located between the cords of an outermost circumferential belt layer in the radial direction and an outer peripheral surface of said outermost circumferential layer is made larger in the central region of the tire than in side end regions thereof in the widthwise direction at a radial section of the tire.