Patent ID: 7520307
Filing Date: 2009-04-21
Classification: B60C,Y10T

Abstract:
1. A pneumatic radial tire comprising a tread portion, a pair of sidewall portions continuously extending from each side end portion of the tread portion inward in a radial direction, a bead portion disposed at an inner peripheral side of the respective sidewall portion, a radial carcass toroidally extending between a pair of bead cores embedded in the respective bead portions and comprised of one or more carcass plies, each side portion of which ply being wound around the bead core outward in the radial direction, and a reinforcing rubber arranged inside the sidewall portion and further inside the radial carcass and having a crescent form at its cross section, in which one or more cord reinforcing layers having a rubberized structure of steel cords are arranged along a turnup portion of the carcass ply around the bead core, and an interval between the steel cords in the cord reinforcing layer is a range of 2.5-20 times a diameter of the cord, wherein the steel cords in the cord reinforcing layer are such a twisted cord that a shear rigidity in a diagonal direction of a square defined by a radial line segment and a circumferential line segment in a plane of the sidewall portion at a part integrally viewing the mutually adjoining cord reinforcing layer and turnup portion of the carcass ply is a range of 300-1000 MPa at a normal state of the tire wherein an elongation of the steel cord is less than 0.5%, and a range of 1000-15000 MPa at a run-flat running of the tire wherein the elongation is not less than 0.5%.