Pneumatic radial tire with asymmetric tread

A pneumatic radial tire having a radial carcass extending between two tire sidewalls through a tire crown portion in toroidal shape;

• a belt layer arranged along an outer circumferential of a crown portion of the carcass;
• and a tread formed with at least one main circumferential groove located at a central portion of the tread substantially in parallel to a tire equator, a plurality of inclination grooves arranged on both sides of a tire tread at substantially regulr intervals along a tire circumference and extending from both tread ends toward the main circumferential groove to form an acute angle with a line parallel to the tire equator, each of said first and second inclination grooves increasing in width toward respective tread ends, and tire land portions partitioned by the main groove and said inclination grooves, wherein a ratio of P.sub.1 /P.sub.2 lies within a range between 1.5 and 3.0 and .alpha..sub.2 is greater than .alpha..sub.1, where:
• P.sub.1 denotes a first circumferential pitch length of said first inclination groove and, where, .alpha..sub.1 denotes a first average inclination angle of first inclination grooves with respect to said line parallel to the tire equator both in a first tire tread area defined between the main circumferential groove and a first tread end;
• and P.sub.2 denotes a second circumferential pitch length of second inclination grooves and .alpha..sub.2 denotes a second average inclination angle of said second inclination grooves with respect to said line parallel to the tire equator both in a second tire tread area defined between the main circumferential groove and a second tread end where P.sub.1 and P.sub.2 are measured at the tread edge in the circumferential direction from the edge of one groove to the same edge on an adjacent groove.