PURPOSE: To improve the high speed durability of the subject heavy load radial tire used for a bus or the like by providing a protective layer of aromatic polyamide fabric cords laid at the predetermined angle between the predetermined carcass and a two-ply belt layer, and applying the predetermined times of cord diameter to a cord distance between belt plies.

CONSTITUTION: A protective layer 6 is provided between a carcass 7 and a belt layer 9 comprising two belt plies 11 and 12 of steel cords laid at an angle equal to or above 10 degrees, but less than 30 degrees orthogonally with each other, and both ends of the protective layer 6 is bent to the outside the belt layer 9. The aforesaid protective layer 5 is constituted with protective cords of aromatic polyamide fabric laid at an angle equal to or above 50 degrees but less than 70 degrees. Also, a radial distance A between the belt cords of adjacent belt plies 11 and 12 is made equal to or above 0.2 times, but less than 2.0 times cord diameter at the ends of the belt plies 11 and 12. According to the aforesaid construction, the high speed durability of the tire can be improved.