Patent ID: 7188655

Claim:
A pneumatic tire, comprising a radial carcass of at least one carcass ply comprised of a main body portion toroidally extending between bead cores respectively embedded in a pair of bead portions, and a turnup portion extending from the body portion and wound around the bead core and a bead filler located just above the bead core, said bead filler being comprised of a lower rubber portion arranged adjacent to an outer circumferential surface of the bead core and an upper rubber portion arranged adjacent to the lower rubber portion and outward therefrom in a radial direction of the tire and having a rigidity lower than that of the lower rubber portion, wherein the tire comprises a reinforcing member consisting of at least two rubberized reinforcing layers each containing steel cords or organic fiber cords arranged in parallel to each other, and at least two reinforcing layers among these reinforcing layers constituting the reinforcing member are cross reinforcing layers arranged so as to envelop at least the turnup portion of the radial carcass and cross the cords of these layers with each other, and both outer ends of the reinforcing layers constituting the cross reinforcing layers located outward from the turnup portion of the radial carcass in a width-wise direction of the tire are located outward from an outer end of the turnup portion of the radial carcass in the radial direction of the tire, and the steel cord or the organic fiber cord constituting each of the reinforcing layers is formed by twisting filaments each having a modulus of elasticity of not less than 40 GPa, and a bending rigidity per one steel cord or one organic fiber cord is not more than 2 GPa·mm 4, and the product of the bending rigidity (GPa·mm 4) per one cord and an end count (cords/mm) in the steel cords or the organic fiber cords is 0.012–0.62 (GPa.mm 4.cords/mm), and a crossing angle (α) between the cords of the adjacent reinforcing layers with respect to a circumferential direction of the tire is more than 50° but less than 130°, wherein the bending rigidity per one cord is represented by the following formula: D= 2N cos β/{[(1+cos 2 β)/EI]+[sin 2 β/GI p ]}, G=E/[ 2(1+μ f )] where N is the number of filaments per each reinforcing layer, β is a twisting angle of the filament, E is a Young's modulus, G is a modulus of transverse elasticity, I is a moment of inertia of area (I=(π/64)×d 4 , I p =(π/32)×d 4 , “d” is a diameter of the filament), and μ f is a Poisson's ratio of the filament.