Patent ID: 6044885
Filing Date: 2000-04-04
Classification: B60C,Y10T

Abstract:
A pneumatic radial tire for trucks and buses mounted on an approved 15.degree. drop center rim comprising a pair of bead portions, a tread portion, at least one carcass ply extending between bead cores embedded one in each bead portion so as to reinforce these portions, the at least one carcass ply being reinforced with cords radially arranged therein and wound around the bead cores from the inside of the tire toward the outside thereof to form a turnup portion in each bead portion and a main body therebetween, each of said bead cores being a wound laminate of steel wire having a round or polygonal shape in cross-section, a belt superimposed on an outer periphery of the at least one carcass ply to reinforce the tread portion and comprised of two or more cross steel cord layers, and a composite side-rubber extending from a bead base of each bead portion through an outside of the bead portion to a tread rubber of the tread portion and consisting of a rubber chafer and a sidewall rubber, an outer surface portion of at least the composite side-rubber among members constituting each bead portion of the tire has a curved shape concavedly directed toward the outside of the tire at a region opposite to an inner curved surface of a slantly rising portion in each flange of the approved rim; and wherein,the concavedly curved surface of the composite side-rubber is located between a bead base line and a first straight line passing through a radially outer surface of a steel wire located at an outermost side of the bead core in the radial direction of the tire and being parallel to the bead base line, and the curve appearing in the concavedly curved surface of the composite side-rubber in cross-section of the tire is comprised of plural arc segments smoothly connecting to each other and having an inwardly directed convex peak in one of these segments, the peak being located between the first straight line and a second straight line passing through an innermost side of the turnup portion of the at least one carcass ply around the bead core in the radial direction of the tire and parallel with the bead base line; andthe concavedly curved surface of the composite side-rubber is formed so that a radius of curvature R.sub.1 of an arc segment having the peak among the arc segments constituting the concavedly curved surface and a radius of curvature R of a major inner curved surface in the flange in cross-section of the approved rim satisfy a relationship of 0.4.times.R.ltoreq.R.sub.1 .ltoreq.1.6.times.R.