To provide a pneumatic radial tire with excellent durability performance in which a steel cord with excellent anti-fatigue property enhancing anti-fretting property while ensuring rubber intrusion property to the inside of the cord is used for a carcass ply.
The steel cord for reinforcing the carcass ply has 1+m+n structure (m is 5 or 6 and n is 10 or 11) that a core filament diameter is 0.22 mm or less, a twisting direction of an inner sheath 13 and an outer sheath 15 is twisted in the same direction, clearances S1, S2 between respective mutual adjacent filaments constituting the inner sheath 13 and the outer sheath 15 are 0.008 mm or more in average. An angle θ formed by twisted angles θ1, θ2 of the inner sheath filament 14 and the outer sheath filament 16 relative to an axis of the steel cord is 10° or less.
COPYRIGHT: (C)2008,JPO&INPIT
Masato Tsuda
Tetsuji Nakamura
Katsuyuki Tomita