The Toyo Rubber Industry Co., Ltd.

Takyya Okazaki

Masanori Kan

Tatsuo Sakashita

A composition for tires containing at least 30% star shaped random styrene-butadiene copolymer obtained by solution polymerization, having a styrene content of less than 20% and more than 10% and a vinyl content of less than 50% and more than 40%, the composition value X of said copolymers being in a range of 26 to 39 obtained by using the equation; ##EQU1## wherein BR is the butadiene component, the glass transition temperature being a single one below -50.degree. C. and lower than estimated glass transition temperature following Gordon-Taylor equation by 5.degree. to 10.degree. C. and a cured composition showing loss modulus of lower than 1.times.10.sup.-7 dyn/cm.sup.2 and a ratio of rolling resistance to wet grip being smaller than 0.82.

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Toyonaka, Japan

Takyya Okazaki