Studless tire

1. A studless tire including a tread portion provided with at least six rows of blocks which are defined by circumferential grooves extending continuously in the circumferential direction of tire and lateral grooves arranged in the circumferential direction in each of said at least six rows, wherein:

each said block is provided with zigzag sipes having a depth of at least 3.0 mm,

said at least six rows of the blocks comprises

at least two crown block rows disposed within a crown region centered on the tire equator and having a width of 50% of the tread width, and

at least two shoulder block rows disposed on each of the axially outer sides of said at least two crown block rows, and

the lateral grooves in each of said at least six rows are inclined in one direction, with respect to the axial direction, oppositely to the lateral grooves in the axially adjacent row or rows of said at least six rows, and

in each of said at least six rows, the blocks therein are provided with a plurality of incisions which extend in one direction opposite to the inclining direction of the lateral grooves therein with respect to the axial direction, and the incisions have a width of 0.1 to 2.0 mm and a depth of 0.1 to 2.0 mm, wherein

said circumferential grooves are an axially inner circumferential groove, a middle circumferential groove and an axially outer circumferential groove disposed on each side of the tire equator,

the axially outer circumferential grooves are straight grooves,

the inner and middle circumferential grooves are zigzag grooves each made up of alternately arranged short segments and long segments,

said at least two crown block rows are three crown block rows comprising a center row disposed on the tire equator and two side rows disposed one on each side of the center row,

the inclination angle θ 1 of the lateral grooves disposed in the center row with respect to the axial direction is smaller than the inclination angle θ 2 of the lateral grooves disposed in the side rows with respect to the axial direction,

said at least two shoulder block rows include an inner shoulder block row disposed on the tire equator side and an outer shoulder block row disposed on the ground contact edge side, and

the inclination angle θ 3 of the lateral grooves disposed in the inner shoulder block row with respect to the axial direction is larger than the inclination angle θ 4 of the lateral grooves disposed in the outer shoulder block row with respect to the axial direction.

2. The studless tire of claim 1 , wherein

in each of said a least six rows, the zigzag sipes therein are inclined in the same direction as the lateral grooves therein.

3. The studless tire of claim 1 , wherein

each said lateral groove has zigzag groove walls.

4. The studless tire of claim 1 , wherein

the inclination angles of said lateral grooves are at least 3 degrees and at most 30 degrees with respect to the axial direction.

5. The studless tire of claim 1 , wherein

the ratio θ 2 /θ 1 of said inclination angle θ 2 in the side rows to said inclination angle θ 1 in the center row is at least 1.2 and at most 2.5.

6. The studless tire of claim 1 , wherein

each said lateral groove has zigzag groove walls,

the inclination angles of said lateral grooves are at least 3 degrees and at most 30 degrees with respect to the axial direction, and

the ratio θ 2 /θ 1 of said inclination angle θ 2 in the side rows to said inclination angle θ 1 in the center row is at least 1.2 and at most 2.5.