Bead structure for pneumatic tire

Claim 2

A bead portion structure (7) in a pneumatic tire (1) comprising a radial carcass (3) comprised of at least one carcass ply (4) containing cords substantially extending in the radial direction of the tire and wound around each of bead cores (2) from the inside toward the outside to form a turnup portion (6), an outer ply (10) inclusive of the turnup portion arranged outside the carcass ply in the axial direction of the tire and extending along the carcass ply and containing cords each having a modulus of elasticity of not less than 2500 kg/mm² and a diameter d, and a rubber stiffener (30) arranged at its radially inward portion between the carcass ply and the outer ply and contacted at its radially inward end with the bead core, characterized in that when positions located on the outer surface of the stiffener and separated from the radially outward end (24) of the outer ply (10) by 1 times and 30 times the cord diameter d in a direction separating from the bead core are A and B, respectively, and an intersection of a straight line L passing the radially outward end of the outer ply and perpendicular to the inner surface of the stiffener with the inner surface of the stiffener is C, and a position located on the inner surface of the stiffener and separated from the intersection C by 30 times the cord diameter d in a direction separating from the bead core is D, and a position located on the inner surface of the stiffener and separated from the intersection C by 10 times the cord diameter d in a direction approaching the bead core is E, and a position located on the outer surface of the stiffener and separated from the radially outward end of the outer ply by 10 times the cord diameter d in a direction approaching the bead core is J, and a position located on the outer surface of the stiffener between the positions A and B is F, and a position located on the inner surface of the stiffener between the positions D and E is G, and a position located on the outer surface of the stiffener and at a side of approaching from the position J to the bead core is K, and a position located on the inner surface of the stiffener and at a side of approaching from the position G to the bead core is M, said stiffener is divided into a base stiffener portion (31) located radially inward from a boundary plane Y connecting the position K to the position M, an inner stiffener portion (32) located radially outward from the boundary plane Y and radially inward from a boundary plane X connecting the position F to the position G and an outer stiffener portion (33) located radially outward from the boundary plane X, and the base stiffener portion is comprised of rubber having a Shore A hardness of not less than 75° and the inner stiffener portion is comprised of rubber having a Shore A hardness of 58° to 68° and the outer stiffener portion is comprised of rubber having a Shore A hardness of not more than 55°, and a volume ratio of the outer stiffener portion in the stiffener is not less than 10%.

Claim 3

A bead structure as claimed in claim 1 or 2, characterized in that said outer stiffener portion (22,33) has a Shore A hardness of 38° to 52°.