PNEUMATIC RADIAL TIRE FOR HEAVY LOAD

摘要

PROBLEM TO BE SOLVED: To provide a pneumatic radial tire for heavy load which does not cause increase in the weight and gives a satisfactorily enhanced durability of bead part without additional provision of reinforcing member. SOLUTION: Rubber members of three layers or more having different hardness are installed in the region from the cord in the carcass ply folded-back part 4t to the outside surface of the bead part 1 among the bead regions corresponding in the normal direction to the contacting surface increasing part with rim flange 10f of the surface of the bead part 1 increasing during the period from the time with the max. air pressure filling for the tire and rim assembly to the time with loading at the max. load ability corresponding load, wherein one layer is formed as covering rubber of carcass ply cord 4 and the softest rubber member 6 of the remaining layer rubber members is arranged adjacent to the outer side face of the covering rubber while the hardest rubber member 7 is arranged adjacent to the outer side face of the softest rubber member, where the 100t% modulus of the softest rubber member 6 is made below 20kgf/ cm and the 100% modulus ratio of the hardest rubber member 7 to the softest rubber member 6 is made over three times as great.