Pneumatic radial tires for construction vehicles

A pneumatic radial tire for construction vehicles comprising;

• a radial carcass of rubberized steel cord ply toroidally extending between a pair of bead cores and wound around the bead core from inside of the tire toward outside to form a turnup portion, a stiffener rubber disposed on the bead core, and at least two reinforcing layers of rubberized fiber cord fabrics having different cord directions and embedded in the stiffener rubber as a bead portion reinforcement so that said reinforcing layers do not extend along an outer surface of the carcass ply and the surface of said turnup portions;
• said reinforcing layer satisfying the following relations:
• .alpha.=(0.5-0.87).H
• .beta.=(0.52-0.78).h
• where:
• .alpha. is a height of an end of the reinforcing layer positioned in the vicinity of the inner surface of the turnup portion and inward in the radial direction of the tire and measured from base line of a normal rim, .beta. is a height of other end of the reinforcing layer positioned in the vicinity of the outer surface of the carcass ply and outward in the radial direction of the carcass ply and outward in the radial direction of the tire and measured from the base line, H is a flange height of the normal rim and h is a height at a position corresponding to maximum width of the carcass measured from the base line, wherein said stiffener rubber is comprised of a hard rubber layer extending closely along the outer surface of the carcass ply above the bead core and outward in the radial direction of the tire to gradually reduce the thickness thereof, and a soft rubber layer extending closely along the inner surface of the turnup portion and the outer surface of the carcass ply outward in the radial direction of the tire, and the reinforcing layer is arranged at the boundary between the hard rubber layer and the soft rubber layer.