PNEUMATIC RADIAL TIRE

PURPOSE:To follow a road surface easily even when grounding pressure distribution changes largely depending on tire running conditions to achieve sufficient edge effect, and improve anti-side slipping performance on an ice and snow road surface extraordinarily. CONSTITUTION:A tire has thin grooves 4a, 4b, 4c, 4c'... formed in blocks 3a, 3b, 3c... formed in a tread surface by plural main grooves 1a, 1b, 1c... extended in the tire circumferential direction and subsidiary grooves 2a, 2b, 2c... extended in the width direction to be extended in the tire circumferential direction to be narrower than the width of the main grooves, and shallower than the depth of them, and to separate each block almost in the similar width. The ratio Ds/S of the total surface Ds of the thin grooves in a tire grounding surface to a total grounding surface S is desirably set within the range of 0.02-0.08, and the depth (h) of the thin grooves in block lines A, B, C... adjacent to each other from a tread center to a tire shoulder is gradually decreased at a specific ratio sigma, or otherwise, their width (w) is gradually increased at a specific ratio delta.