Heavy duty pneumatic radial tire with a carcass ply composed of aromatic

Abstract

A heavy duty pneumatic radial tire is disclosed, which comprises a single carcass ply having aromatic polyamide fiber cords at a cord angle of about 90.degree. relative to a tire equatorial plane, a pair of bead cores, and first and second reinforcing layers successively laminated axially outside turn-up portions of the carcass ply. A height of the turn-up portion is from 0.075 to 0.16 time that of the carcass ply in a tire section. The first reinforcing layer comprises steel cords arranged obliquely to the carcass ply cords, and has a radially outer end higher than an end of the turn-up portion. The following relation exists among a.sub.1, d.sub.1, a.sub.2, d.sub.2, T.sub.1 and T.sub.2 : ##EQU1## in which a1, d.sub.1, a.sub.2, d.sub.2, T.sub.1, and T.sub.2 are a radius (mm) and an interval (mm) of the steel cords of the first reinforcing layer at the radially outer end, a radius (mm) and an interval (mm) of the cords of the carcass ply, a tenacity(kg) of a single cord of the first reinforcing layer, and a tenacity (kg) of a single cord of the carcass ply, respectively. The second reinforcing layer consists of at least two reinforcing layer units each having organic fiber cords intersecting between the layer units, and is continuously turned up from an axially outside of the first reinforcing layer to the inside of the carcass ply. The radially outer end of the second reinforcing layer is higher by 5 to 20 mm than of the first reinforcing layer. The radially outer ends of the second reinforcing layer units are vertically spaced from each other by 5 to 20 mm. The axially outermost second reinforcing layer unit is positioned highest. The cords of the axially inner second reinforcing layer unit intersect with those of the first reinforcing layer.