A rubber composition favorably used for a reinforcing layer of a run flat
tire, which have both low exothermic property and high strength.A rubber
composition for a tire, comprising 10 to 100 parts by weight of carbon
black having a nitrogen adsorbing-specific area of 30 to 100 m.sup.2/g
and a dibutyl phthalate oil absorption amount of at least 50 ml/100 g and
at least 2 parts by weight of sulfur or a sulfur compound based on 100
parts by weight of a rubber component containing 10 to 70% by weight of a
butadiene rubber obtained by copolymerizing a compound represented by the
formula (1): ##STR00001## (wherein R.sup.1 represents an amino group, an
alkoxy group, a silyloxy group, an acetal group, a carboxyl group, a
mercapto group or derivatives thereof).