A rubber composition for tires comprises a diene rubber, silica, and a silane coupling agent, and is characterized in that a function v of a shear modulus G′ of the rubber composition at 0.28% shear stress at 110° C., a CTAB specific surface area (CTAB) of the silica, a volume fraction (φ) of the silica in the rubber composition, and a stress at 100% elongation (M100) of the rubber composition satisfies the relationship of the following equation (i): G′=K×v, where K is a coefficient greater than 0 and not greater than 450, and v is represented by the following equation (ii): v=φ×(1+0.0258×CTAB×M100) and is a real number not less than 2.5 and not greater than 20.