Abstract: A pneumatic radial tire for truck and bus comprises a carcass ply containing cords arranged substantially in a radial direction of the tire and a belt superimposed about said carcass ply and comprised of plural belt layers each containing steel cords arranged at a cord angle of 5.degree.-20.degree. with respect to an equator of the tire. In this case, the steel cord for the belt layer has a two-layer structure of a core comprised of two steel filaments and a single sheath comprised of 6-8 steel filaments and satisfies the particularly relationships on filament diameter, twisting pitch, bending rigidity, tensile strength and distance between adjoining cords.

Abstract: A pneumatic radial tire for truck and bus comprises a carcass ply containing cords arranged substantially in a radial direction of the tire and a belt superimposed about said carcass ply and comprised of plural belt layers each containing steel cords arranged at a cord angle of 5.degree.-20.degree. with respect to an equator of the tire. In this case, the steel cord for the belt layer has a two-layer structure of a core comprised of two steel filaments and a single sheath comprised of 6-8 steel filaments and satisfies the particularly relationships on filament diameter, twisting pitch, bending rigidity, tensile strength and distance between adjoining cords.

Abstract: A heavy duty pneumatic radial tire comprises at least one carcass ply reinforced with steel cords substantially arranged at an angle of 90.degree. with respect to an equator of the tire and wound around a bead core from inside of the tire toward outside thereof. In this tire, the steel cord is made from steel wires each having a tensile strength of 330-400 kg/mm.sup.2 and a cementite lamellar distance of 120-190 .ANG., a residual stress of whose is compression stress at a depth within a range of 1/10 to 1/5.5 of a wire diameter from the surface of the steel wire.

Abstract: In a heavy duty radial tire, metal cords of a single layer construction obtained by twisting 3.about.5 metallic filaments having a filament diameter of 0.13.about.0.32 mm, each of which cords having an elongation P.sub.1 under a load of 0.25.about.5 kgf/cord of 0.35.about.1.0% as an arithmetic mean value are arranged as a carcass ply so that a distance between cords at an end of the carcass ply is not less than 0.25 mm. Thus, it is possible to largely reduce the tire weight, avoid problems on the operability such as bead rising and the like, and considerably improve the fracture resistance, corrosion fatigue resistance and fretting resistance at carcass ply end as well as resistance to external damage in sidewall (resistance to cord breaking up) of the radial tire.

Abstract: A large-size pneumatic radial tire for use on rough road is disclosed, which comprises as a tire reinforcement a carcass ply of cords arranged in a direction substantially perpendicular to the equatorial plane of the tire and a belt composed of at least three cord layers each containing steel cords embedded parallel to each other in rubber and arranged at a relatively small angle with respect to the equatorial plane of the tire, at least a pair of adjacent cord layers among which being piled one upon the other to cross their cords with each other at an angle of 15.degree.-30.degree. with respect to the equatorial plane. In this type of the tire, the outermost cord layer for the belt is a cord layer formed by embedding a plurality of twisted steel cords, each having a single layer construction of 1.times.3, 1.times.4 or 1.times.

Abstract: A radial tire has a combined reinforcement consisting of a belt composed of at least three piled cord layers with steel cords buried in parallel in rubber in which the cords in each of the layers are set at a relatively small angle with respect to a tire equatorial plane and the cords in at least one pair of the adjacent cord layers are intersectingly arranged at an angle from 15.degree. to 30.degree. and a carcass having cords arranged substantially at right angles with respect to the tire equatorial plane. The steel cords buried in the at least one pair of the cord-intersecting cord layers other than the outermost cord layer have Young's modulus of 6,000 to 16,000 kg/mm.sup.2 and a flexural rigidity of 150 to 250 g, and the initial stage elongation (P.L.E.) of the rubberized cords taken out from the tire is not more than 0.2%.

Abstract: A pneumatic radial tire having an improved durable life is disclosed. In the pneumatic radial tire, a metal cord used in the carcass ply is characterized by having a layer construction of 3+9+1 wherein three filaments are twisted together to form a core, nine filaments each having the same diameter as in the filament for the core are twisted around the core to form a second layer and a single filament is wrapped around the second layer, and limiting a twisting angle .alpha. of the second layer to a range of 72.0.degree..ltoreq..alpha..ltoreq.78.0.degree..