Pneumatic tire

1. A pneumatic tire comprising

a tread portion provided with a center main groove extending continuously in the tire circumferential direction,

a pair of middle main grooves extending continuously in the tire circumferential direction on both sides of the center main groove,

a pair of shoulder main grooves extending continuously in the tire circumferential direction between the middle main grooves and tread edges,

a plurality of center lateral grooves connecting between the center main groove and the middle main grooves,

a plurality of middle lateral grooves connecting between the middle main grooves and the shoulder main grooves, and

a plurality of shoulder lateral grooves connecting between the shoulder main grooves and the tread edges, so as to have

a pair of center block rows of center blocks which are divided by the center main groove, the middle main grooves and the center lateral grooves, and arranged at intervals in the tire circumferential direction,

a pair of middle block rows of middle blocks which are divided by the middle main grooves, the shoulder main grooves and the middle lateral grooves, and arranged at intervals in the tire circumferential direction, and

a pair of shoulder block rows of shoulder blocks which are divided by the shoulder main grooves, the tread edges and the shoulder lateral grooves, and arranged at intervals in the tire circumferential direction,

wherein

all of said plurality of center lateral grooves have the same groove width WA,

all of said plurality of middle lateral grooves have the same groove width WB,

all of said plurality of shoulder lateral grooves have the same groove width WC,

the groove width WA of the center lateral grooves is equal to the groove width WB of the middle lateral grooves, and

a ratio WC/WA of a groove width WC of the shoulder lateral grooves and the groove width WA of the center lateral grooves is 1.3 to 2.3,

wherein

the center main groove is disposed on the tire equator,

a groove width of each of the shoulder main grooves is larger than a groove width of the center main groove, and

a groove width of each of the middle main grooves is larger than the groove width of each of the shoulder main grooves, and

wherein the tread portion is provided with a directional pattern which is symmetrical about the tire equator except that one half of the pattern on one side of the tire equator is shifted in a circumferential direction from the other half of the pattern on the other side of the tire equator by half a pitch.

2. The pneumatic tire as set forth in claim 1 , wherein the ratio WC/WA of the groove width WC of the shoulder lateral grooves and the groove width WA of the center lateral grooves is 1.6 to 2.0.

3. The pneumatic tire as set forth in claim 1 , wherein

the groove width WA of the center lateral grooves,

the groove width WB of the middle lateral grooves, and

the groove width WC of the shoulder lateral grooves are not less than 4 mm.

4. The pneumatic tire as set forth in claim 1 , wherein

a ratio Lc/Lm of a land ratio Lc of a center region which is a region between tire-circumferential-direction lines extending parallel with the tire circumferential direction, passing through both ends in the tire axial direction of the center blocks, and

a land ratio Lm of a middle area which is a region between tire-circumferential-direction lines extending parallel with the tire circumferential direction, passing through both ends in the tire axial direction of the middle blocks is 1.05 to 1.25.

5. The pneumatic tire as set forth in claim 1 , wherein the angle with respect to the tire axial direction of the center lateral grooves is 10 degrees to 30 degrees.

6. The pneumatic tire as set forth in claim 1 , wherein

the middle main grooves and the shoulder main grooves are formed zigzag,

the middle main grooves are intersected by the center lateral grooves and the middle lateral grooves at zigzag vertexes of the middle main grooves, and

the shoulder main grooves are intersected by the middle lateral grooves and the shoulder lateral grooves at zigzag vertexes of the shoulder main grooves.

7. The pneumatic tire as set forth in claim 1 , wherein the tread portion is provided with a directional pattern for which a rotational direction is specified.

8. The pneumatic tire as set forth in claim 7 , wherein

the center lateral groove is inclined to a later-contacting-side in the rotational direction from the inner end in the tire axial direction toward the outer end, and

the middle main groove is zigzag such that short segments and long segments are alternately arranged,

wherein

the short segments are inclined to the same direction as the center lateral grooves, and the long segments are longer in the circumferential length than the short segments and are inclined to the opposite direction to the short segments, and

the center lateral grooves are connected to the short segments of the middle main grooves.

9. The pneumatic tire as set forth in claim 8 , wherein the center lateral groove has a tie bar raising from the groove bottom and connecting between the adjacent center blocks.

10. The pneumatic tire as set forth in claim 8 , wherein

the middle lateral grooves are inclined to the same direction as the center lateral grooves,

the shoulder main groove has short segments inclined to the same direction as the middle lateral grooves, and long segments being longer in the circumferential length than the short segments and inclined to the opposite direction to the short segments, and

the middle lateral grooves are connected to the short segments of the shoulder main groove.

11. The pneumatic tire as set forth in claim 8 , wherein

the center lateral grooves on both sides of the center main groove are arranged so that those on one side shift in the tire circumferential direction from those on the other side,

the center lateral grooves and the middle lateral grooves on both sides of the middle main groove are arranged so that those on one side shift in the tire circumferential direction from those on the other side, and

the middle lateral grooves and the shoulder lateral grooves on both sides of the shoulder main groove are arranged so that those on one side shift in the tire circumferential direction from those on the other side.

12. The pneumatic tire as set forth in claim 8 , wherein

an angle γ1 with respect to the tire circumferential direction of the center lateral grooves is smaller than an angle γ2 with respect to the tire circumferential direction of the middle lateral grooves, and

the angle γ2 with respect to the tire circumferential direction of the middle lateral grooves is smaller than an angle γ3 with respect to the tire circumferential direction of the shoulder lateral grooves.

13. The pneumatic tire as set forth in claim 12 , wherein

the angle γ1 respect to the tire circumferential direction of the center lateral grooves is 60 degrees to 80 degrees, and

the angle γ3 with respect to the tire circumferential direction of the shoulder lateral grooves is 80 degrees to 90 degrees.

14. The pneumatic tire as set forth in claim 1 , wherein

the middle main grooves and the shoulder main grooves are formed zigzag,

the middle main grooves are intersected by the center lateral grooves and the middle lateral grooves at zigzag vertexes of the middle main grooves, and

the shoulder main grooves are intersected by the middle lateral grooves and the shoulder lateral grooves at zigzag vertexes of the shoulder main grooves.