Radial tire having polyester cord breaker

Claim 1

In a radial tire having a tread portion, a pair of side portions extended to the tread portion at both the shoulders thereof, a pair of bead portions formed in the inner peripheries of the side portions respectively, a breaker formed inside the tread portion along its peripheral direction, and a carcass, the improvement characterized by: a. the breaker comprising adhesive treated, heat set polyester cords formed of twisted yarns, b. each yarn comprising a bundle of a plurality of filaments consisting of polyester having a low polymerization degree and an intrinsic viscosity of 0.3-0.8 measured in o-chlorophenol at 25*C, c. the twisting being performed at a twisting coefficient (NT) of 0.15-0.45, said twisting coefficient being expressed by the following formula: NT N X square root 0.139 X D/ Rho X 10 3 wherein N is the number of cable twists per 10 cm of cord, D is one-half of the total deniers of cord, and Rho is the density of fiber, d. the cords being treated with an adhesive to implement their adherance to rubber, and e. the heat setting being performed at a temperature of 230*255*C for 2-4 minutes under a tension of 0.15-1.0 g/denier.