Large-size pneumatic radial tire for use on rough road with belt having specified cord

A large-size pneumatic radial tire for use on rough road comprising as a tire reinforcement;

• a carcass ply of cords arranged in a direction substantially perpendicular to the equatorial plane of the tire and a belt composed of at least three cord layers each containing steel cords embedded parallel to each other in rubber and arranged at a relatively small angle with respect to the equatorial plane of the tire, at least two adjacent cord layers of said cord layers of the belt being piled one upon the other to cross their cords with each other at an angle of 15.degree.-30.degree. with respect to the equatorial plane, an outermost cord layer for said belt comprising a cord layer formed by embedding a plurality of twisted steel cords, each having an elongation at break of 3.0-5.5% and a single layer construction of 1.times.3, 1.times.4, or 1.times.5 or a double layer construction with a core of 1 to 2 filaments obtained by twisting plural steel filaments shaped prior to the formation of cord at a twisting angle of 10-20 without a wrap filament in rubber at a cord volume fraction of 5-40%, which is expressed by a percentage of the sum of sectional areas of cords included in an area of a region defined by a bisector between a line passing through centers of the cords in the outermost cord layer for the belt and a line passing through centers of the cords in an inner cord layer adjacent to the outermost cord layer and borderline between the tread and the outermost cord layer in section perpendicular to the circumferential direction of the belt, in such a manner that the form of penetrating rubber into the inside of the cord is a sealing type penetration from wherein a portion of the cord having an inner space completely filled with the penetrated rubber and a longitudinal length l.sub.1 is alternately connected with a portion of the cord having an inner space incompletely filled with the penetrated rubber and a longitudinal length l.sub.2 in the longitudinal direction of the cord so as to satisfy l.sub.2 of not more than 10 mm and l.sub.1 /l.sub.2 of not less than 0.14.