Pneumatic radial tire with high cornering and steering stability

A pneumatic tire comprising a carcass in radical structure extending from a tread part through side wall parts and folded at each edge around a bead core of a bead part, and a belt layer composed of more than two belt plies disposed radially outside said carcass, said belt layer having a pair of axial outer edges, each of said pair of axial outer edges being defined where the two widest belt plies overlap, wherein;

• a tread surface is formed along a specific curvature plane which includes a first arc with the curvature radius R1 having a center on the tire's equatorial plane and passing through the tire's equatorial point, a second arc with the curvature radius R2 having a center on the tire's equatorial plane and intersecting with said first arc at an intersection distance from the tire's equatorial plane by 0.2 to 0.25 times the tire width SW, and a third arc with the curvature radius R3 passing through a ground contact outer edge point of the ground contact surface in the axial direction of a tire when a standard load is applied and a belt intermediate height point on the tread surface,
• said belt intermediate height point on the tread surface being defined as a point at which a tire axial direction line crosses the tread surface extending in parallel with the tire's axis from a thickness center of one of said pair of axial outer edges;
• and
• the tread surface is provided with a pair of main circumferential grooves, one of said main circumferential grooves extending on each side of the tire's equatorial plane at said intersection of the first arc and the second arc in the tire circumferential direction for dividing the tread surface into a crown part and an outer shoulder part, each said main circumferential groove having a groove width of 0.06 to 0.10 times the tire width SW, and with a plurality of narrow lateral grooves crossing the tire circumferential direction for dividing the crown part and the shoulder parts into a plurality of blocks, wherein
• the specific curvature plane has a curvature radius ratio R2/R3 in a range from 4 to 12, and a curvature radius ratio R1/R2 in a range from 1.6 to less than 2.6 when the aspect ratio H/SW of the tire sectional height H to the tire width SW is more than 0.55 and less than 0.70.