A tire having, on a tread portion, a plurality of circumferential grooves (2,2A) extending in a tire circumferential direction, and plural lateral grooves each communicating adjacent two circumferential grooves (2,2a), thereby defining a plurality of block land portion arrays formed by a large number of block land portions, wherein: between block land portion arrays located adjacent to each other while sandwiching the circumferential groove (2,2a), the block land portions constituting said block land portion arrays are arranged so as to be positionally displaced from each other in the tire circumferential direction; a groove portion between the block land portions adjacent in the tire width direction extends obliquely with respect to the tire width direction and the tire circumferential direction; a distance (d 2) between the block land portions adjacent in the tire width direction is shorter than a distance (d 1) between the block land portions adjacent in the tire circumferential direction; a length of the block land portion in the widthwise cross section of the tire increases from both edge portions of the block land portion in the circumferential direction toward a central portion of the block land portion; and, among side walls (9,10) of the block land portion in block land portion arrays adjacent in the tire width direction, an inclined angle (β) of a side wall located on the groove portion side between the block land portions adjacent in the tire width direction with respect to the tire circumferential direction is larger than an inclined angle (a) of the other side wall located on the opposite side to said groove portion as viewed from the tire width direction with respect to the tire circumferential direction, wherein in the tire width direction the block land portion is provided with a narrow groove communicating in said block land portion two adjacent circumferential grooves (2.2a), characterised in that the length of the narrow groove in the tire circumferential direction is in the range of 5 to 20% of a depth of the lateral groove. between block land portion arrays located adjacent to each other while sandwiching the circumferential groove (2,2a), the block land portions constituting said block land portion arrays are arranged so as to be positionally displaced from each other in the tire circumferential direction; a groove portion between the block land portions adjacent in the tire width direction extends obliquely with respect to the tire width direction and the tire circumferential direction; a distance (d 2) between the block land portions adjacent in the tire width direction is shorter than a distance (d 1) between the block land portions adjacent in the tire circumferential direction; a length of the block land portion in the widthwise cross section of the tire increases from both edge portions of the block land portion in the circumferential direction toward a central portion of the block land portion; and, among side walls (9,10) of the block land portion in block land portion arrays adjacent in the tire width direction, an inclined angle (β) of a side wall located on the groove portion side between the block land portions adjacent in the tire width direction with respect to the tire circumferential direction is larger than an inclined angle (a) of the other side wall located on the opposite side to said groove portion as viewed from the tire width direction with respect to the tire circumferential direction, wherein in the tire width direction the block land portion is provided with a narrow groove communicating in said block land portion two adjacent circumferential grooves (2.2a), characterised in that the length of the narrow groove in the tire circumferential direction is in the range of 5 to 20% of a depth of the lateral groove.