Patent ID: 8232352

Claim:
A rubber composition characterized by compounding a filler to a rubber component containing (A) a modified conjugated diene rubber having a cis-bond content in conjugated diene portion of not less than 87% and a vinyl bond content of not more than 2% and containing a functional group reactive with a filler and produced by coordination polymerization and (B) a modified polymer having a modifying functional group number per 1 molecule of an unmodified polymer of not less than 0.6 and produced by anion polymerization, and satisfying a relation of the following equation (I) with the filler, the conjugated diene rubber (A) and the modified polymer (B): S F ×W F ×10 7 /( W A ×f A /M n ,( A )+ W B ×f B /M n ( B ))≦11 (I) wherein S F : cetyltrimethylammonium bromide (CTAB) adsorption specific surface area (m 2 /g) of a filler, W F : amount (parts by mass) of a filler compounded per 100 parts by mass of a rubber component, W A : amount (parts by mass) of a modified conjugated diene rubber (A) compounded per 100 parts by mass of a rubber component, W B : amount (parts by mass) of a modified polymer (B) compounded per 100 parts by mass of a rubber component, M n (A): number average molecular weight of a modified conjugated diene rubber (A), M n (B): number average molecular weight of a modified polymer (B), f A : modifying functional group number per 1 molecule of a modified conjugated diene rubber (A), and f B : modifying functional group number per 1 molecule of a modified polymer (B).