Pneumatic radial tire

A pneumatic radial tire having a tread pattern comprising;

• blocks having sidewalls with a slope and arranged on a tread surface thereof and partitioned by a pair of first relatively wide main circumferential grooves (10.sub.1) formed at a tread crown portion thereof, at least a pair of second relatively narrow main circumferential grooves (10.sub.2) extending in parallel to an axially outside the first main circumferential grooves, and transverse grooves intersecting the first and second main circumferential grooves being inclined at an angle thereto, wherein said blocks are formed into different shapes such that difference in angle, measured between adjacent block sidewall surfaces to define corners, between acute angle corners and obtuse angle corners is different on the tread surface;
• and a different (.beta..sub.1 -.beta..sub.3) in inclination angle measured between the block sidewall slope and a line perpendicular to the tread surface, between the acute angle corners (30a) and the obtuse angle corners (30b) is increased in proportion to the difference in angle between the acute angle corner and the obtuse angle corner, said inclination angle gradually increasing from the obtuse angle corner to an acute angle corner.

A pneumatic radial tire having a tread pattern comprising;

• blocks having sidewalls with a slope and arranged on a tread surface thereof and partitioned by a pair of first relatively wide main circumferential grooves (10.sub.1) formed at a tread crown portion thereof, at least a pair of second relatively narrow main circumferential grooves (10.sub.2) extending in parallel to and axially outside the first main circumferential grooves, and transverse grooves intersecting the first and second main circumferential grooves being inclined at an angle thereto, wherein block sidewalls extending along at least one circumferential side of said blocks are sloped outwardly down in such a way that a width at a bottom of a main circumferential groove is inversely proportional to an inclination angle (.beta.) of said block sidewalls, as measured between the block sidewall slope and a line perpendicular to the tread surface, said inclination angle changing on said block sidewall along said circumferential side, and a width of a top of the groove is uniform along the circumferential direction of the tire.