Rubber composition for tires

A rubber composition for tires, comprising a rubber ingredient selected from the group consisting of natural rubber, diene series synthetic rubber and a blend thereof, and 30.about.150 parts by weight of a reinforcible carbon black having a specific surface area (N.sub.2 SA) of 70.about.250 m.sup.2 /g as measured by nitrogen adsorption process, a dibutyl phthalate absorption (DBP absorption) of 80.about.150 ml/100 g, a concentration of total acidic group introduced into the surface of carbon black of 0.25.about.2.0 .mu.eq/m.sup.2, a ratio of weak acidic group in the total acidic group of at least 65% and a pH value of 3.about.5.5, 0.about.40 parts by weight of silica based on 100 parts by weight of said rubber ingredient, and 4.65.times.10.sup.-5 m.multidot.s.about.4.65.times.10.sup.-3 m.multidot.s (m is parts by weight of carbon black added and s is a value of N.sub.2 SA of carbon black) of at least one silane coupling agent selected from compounds having the following general formulae (1) and (2):

• Y.sub.3 --Si--C.sub.n H.sub.2n S.sub.m C.sub.n H.sub.2n Si--Y.sub.3
• or
• Y.sub.3 --SiC.sub.n H.sub.2n X (1)
• wherein X is a nitroso group, a mercapto group, an amino group, an epoxy group, a vinyl group, a chlorine atom or an imido group, Y is an alkyl group or an alkoxyl group having a carbon number of 1.about.4 or a chlorine atom, and each of n and m is an integer of 1.about.6;
• and
• Y.sub.3 SiC.sub.n H.sub.2n S.sub.m S' (2)
• wherein X' is ##STR6## and Y, m and n are the same as described above.