Patent ID: 8733411

Claim:
A pneumatic tire comprising a tread portion provided with a unidirectional tread pattern having an intended rotational direction and including a pair of right-hand and left-hand crown circumferential grooves which are disposed one on each side of the tire equator and extend continuously in the tire circumferential direction so as to form a circumferentially continuously extending crown rib therebetween, a shoulder circumferential groove extending continuously in the tire circumferential direction and disposed on the axially outside of each of the crown circumferential grooves, and middle axial grooves extending from said shoulder circumferential groove to the crown circumferential groove, while inclining to the rotational direction, so that a row of circumferentially arranged middle blocks is formed, the crown rib being provided with first V-shaped grooves and second V-shaped grooves arranged alternately in the tire circumferential direction, wherein each of the axial edges of the crown rib is made up of straight segments defined between the circumferentially adjacent open ends of the V-shaped grooves, and wherein the straight segments are inclined to the tire equator toward the rotational direction so that one circumferential end of each of the straight segments is axially shifted from the circumferentially adjacent other circumferential end of one of the circumferentially adjacent straight segments, each of the first V-shaped grooves extending from its open end at the left-hand crown circumferential groove to its closed end positioned between the right-hand crown circumferential groove and the tire equator, and each of the second V-shaped grooves extending from its open end at the right-hand crown circumferential groove to its closed end positioned between the left-hand crown circumferential groove and the tire equator, wherein each of the first and second V-shaped grooves is made up of a primary part extending from the open end thereof towards the tire equator while inclining to one circumferential direction corresponding to the rotational direction, and a secondary part extending from the primary part to the closed end while inclining to the other circumferential direction opposite to the rotational direction, wherein a bending point between the primary part and secondary part is substantially positioned at the tire equator, wherein each of the crown circumferential grooves has an axially outer edge extending straight in parallel with the tire circumferential direction, and the axially outer edges of the middle blocks are inclined to the axially outside toward the rotational direction so that, toward the rotational direction, the width of each of the shoulder circumferential grooves is periodically decreased along the shoulder circumferential groove, whereas the width of each of the crown circumferential grooves is periodically increased along the crown circumferential groove.