| 摘要 |
PROBLEM TO BE SOLVED: To improve stable controllability and durability by expressing the coefficient of primary twist and the coefficient of final twist in formulas, and arranging a carcass ply cord so as to be at a fixed angle against the equatorial direction of a tire. SOLUTION: The coefficient of primary twist N1 and the coefficient of final twist N2 satisfy N1 =n1×(0.139×D1 /f)<1/2>×10<-3> , N2 =n2×(0.139×D2 /f)<1/2>×10<-3> , and 1.45<=N2 /N1 <=4.25. In the formulas, n1 expresses the primary-twist-number/10 cm, n2 expresses the final-twist-number/10cm, D1 expresses the nominal denier of primary twist yarn, D2 expresses the total nominal denier of cord, and f expresses the specific gravity of fiber g/cm<3> . A carcass ply cord 16 is arranged so as to be at angle 75 deg.-90 deg. against the equatorial direction of a tire 10. When the ratio N2 /N1 of the coefficient of final twist N2 and the coefficient of primary twist N1 exceeds 4.25, tensile rigidity of the cord is improved but fatigue resistance is lowered, and when it is under 1.45, the cord tensile rigidity is not improved.
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