The present technology provides a rubber composition containing: from 20 to 40 parts by weight of carbon black, from 15 to 30 parts by weight of silica, from 2.0 to 3.5 parts by weight of sulfur, and a sulfur-containing silane coupling agent, per 100 parts by weight of diene rubber that contains from 80 to 100 wt. % of natural rubber, and from 20 to 0 wt. % of isoprene rubber; the total amount of sulfur in the sulfur and the sulfur-containing silane coupling agent being from 2.3 to 4.0 parts by weight.