Pneumatic radial tires for heavy vehicles

In a pneumatic radial tire for heavy vehicles comprising a carcass composed of at least one ply of cords,each being arranged in a radial plane inclusive of the rotary axis of the tire or inclined at an extremely small angle with respect to the radial plane, the carcass being wound around a bead cord from the inside toward the outside thereof to form a turnup portion to sandwich a rubber stock disposed on the bead core, the improvement comprising;

• a bead portion reinforcement containing at least three organic fiber cord layers each arranged toward the outside of the bead core and containing cords crossed with the cords of the carcass ply, said organic fiber cord layers having different heights in their upward ends as measured from a reference line parallel to the rotary axis of the tire passing through the center of the bead core toward the radial direction of the tire and having cords with substantially the same modulus of elasticity, the height of the upward ends of cords of said organic fiber cord layers lowering outwardly toward the axis direction of the tire and, the cords of said organic fiber cord layer, crossed with each other such that the cords of each of the organic fiber cord layers are inclined at a larger angle with respect to the radial plane of the tire as the heights of the upward ends decrease.