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 polyethylene terephthalate or nylon fiber and has a layer twisting structure and a total denier D.sub.T of 1000 d-6000 d and a twist constant N.sub.t =T.times.(0.139.times.D.sub.T /2.times.1/.rho.).sup.1/2 .times.10.sup.-3 .ltoreq.0.3 wherein T is a twisting number (twist turns/10 cm) and .rho. is a specific gravity, wherein each cord for the at least one circumferential belt layer has a loss tangent (tan .delta.) of not more than 0.3 under conditions that an initial tension is 1 kgf/cord, a strain amplitude is 0.1%, a frequency is 20 Hz and an atmosphere temperature is 25.degree. C., and wherein a coating rubber for the at least one circumferential belt layer has a modulus of elasticity of not less than 200 kgf/mm.sup.2.

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 polyethylene terephthalate or nylon fiber and has a layer twisting structure and a total denier D.sub.T of 1000 d-6000 d and a twist constant N.sub.t =T.times.(0.139.times.D.sub.T /2.times.1/.rho.).sup.1/2 10.sup.-3 .ltoreq.0.3 wherein T is a twisting number (twist turns/10 cm) and p 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, a width (L2) of the central region being 50-90% of a width (L1) of the slant belt layer centering around the equatorial plane of the tire.

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 polyethylene terephthalate or nylon fiber and has a layer twisting structure and a total denier D.sub.T of 1000 d-6000 d and a twist constant N.sub.t =T.times.(0.139.times.D.sub.T /2.times.1/.rho.).sup.1/2 .times.10.sup.-3 .ltoreq.0.3 wherein T is a twisting number (twist turns/10 cm) and .rho. is a specific gravity,

• wherein a gauge (t2) of the rubber located between the cords of an outermost circumferential belt layer in the radial direction and an outer peripheral surface of said outermost circumferential belt layer is made larger in the central region of the tire than in the side end regions thereof in the widthwise direction at a radial section of the tire.