A structure for a radial tire for trucks and buses having textile cords in its carcass ply layer and steel cords in its belt layer is disclosed. The tire of this invention has a tread angle within a certain range, which angle is taken such as to be constituted by a line directed from a width-end point of the tire to a width-end point of the tread and a line directed from the width-end point of the tread in the straight vertical direction. More specifically, the ratio of the width of the tread to the width of the tire is so arranged that the tread angle with full air pressure be 17.degree..+-.3.degree. and the difference between the tread angle with full air pressure and the tread angle with an air pressure of 0.5 kg/cm.sup.2 be 3.degree. or less.