Rubber composition for tire and studless tire

A studless tire for a passenger vehicle having

• a tread formed from a rubber composition comprising a rubber component and silica,
• wherein the rubber component includes a modified natural rubber with a phosphorus content of 200 ppm or less, and butadiene rubber, wherein the amount of the modified natural rubber in 100% by mass of the rubber component is 30 to 80% by mass, and the amount of the butadiene rubber in 100% by mass of the rubber component is 20 to 60% by mass;
• and
• the silica has a CTAB specific surface area of 180 m2/g or more and a BET specific surface area of 185 m2/g or more, the amount of the silica is 5 to 100 parts by mass per 100 parts by mass of the rubber component, the D50 of the silica is 2.0 to 7.0 μm, the proportion of the silica whose particle size is larger than 18 μm is 6% by mass or less, the distribution width W of the pore volume of the silica is 0.7 to 5.0, and the diameter Xs that gives the peak value Ys of the pore volume in the pore distribution curve of the silica is 10 to 60 nm.