The present technology provides a rubber composition having: from 30 to 50 parts by mass of carbon black having a nitrogen adsorption specific surface area of from 100 to 130 m2/g, from 25 to 40 parts by mass of carbon black having a nitrogen adsorption specific surface area of from 37 to 60 m2/g, from 1.5 to 2.2 parts by mass of sulfur as a pure sulfur content, and from 110 to 200 mass % of a sulfenamide-based vulcanization accelerator relative to the pure sulfur content compounded in 100 parts by mass of diene rubber containing from 30 to 60 parts by mass of isoprene rubber and from 40 to 70 parts by mass of butadiene rubber.