Patent ID: 7886791

Claim:
A pneumatic radial tire for a passenger car comprising a pair of bead portions and a carcass comprised of at least one carcass ply toroidally extending between a pair of bead cores embedded in the respective bead portions and containing organic fiber cords, characterized in that the organic fiber cord constituting the carcass ply is a polyketone fiber cord satisfying the following equation I: σ≧−0.01 E +1.2 and σ≧0.02 I wherein σ is a thermal shrinkage stress at 177° C. cN/dtex and E is an elastic modulus at 25° C. under a load of 49N cN/dtex and the polyketone fiber cord has a ply-twisting coefficient N 1 defined by the following equation II of 0.35-0.70 and a cable-twisting coefficient N 2 defined by the following equation III of 0.50-0.95: N 1 =n 1 ×(0.125× D 1 /ρ) 1/2 ×10 −3 II N 2 =n 2 ×(0.125× D 2 /ρ) 1/2 ×10 −3 III in the equations II and III, n 1 is a ply twisting number turns/10 cm, n 2 is a cable twisting number turns/10 cm, D 1 is dtext of ply-twisted yarn, D 2 is a total dtex, and ρ is a specific gravity of the polyketone cord g/cm 3 .