Pneumatic tire with tread having continuous ribs and a block row

A pneumatic tire comprising:

• four main grooves that are in a ground contact region of a tread surface and that extend linearly in a tire circumferential direction;
• and
• five land portions on the tread surface partitioned by the main grooves, wherein
• centers of two main grooves positioned on a tread center side among the four main grooves sandwich a tire equator and are formed in positions removed from the tire equator by from 8 to 12% of a tire ground contact width,
• centers of two main grooves positioned on both shoulder sides are formed in positions removed from the tire equator by from 18 to 32% of the tire ground contact width, and
• a groove width of a main groove positioned at a first farthest tire width direction side is less than groove widths of the other three main grooves so that a ratio Wmax/Wout of a maximum groove width Wmax of the three main grooves to a groove width Wout of the main groove positioned at the first farthest tire width direction side is set to from 2.0 to 3.0;
• only a land portion positioned at the first farthest tire width direction side among the five land portions is formed into a block row by being partitioned with lug grooves at a given spacing in the tire circumferential direction, and
• the other four land portions are formed into continuous ribs in the tire circumferential direction;
• and
• a ratio Sin/Sout of a groove area proportion Sin on a second tire width direction side to a groove area proportion Sout on a first tire width direction side when the tire equator is taken as a center in the ground contact region is set to from 1.25 to 1.35, and
• groove area proportions of ground contact regions of the three land portions excluding those at the first farthest tire width direction side and a second farthest tire width direction side among the five land portions are larger in the second tire width direction side than the first tire width direction side with center lines of the land portions as boundaries.