Pneumatic tire

1. A pneumatic tire comprising:

a tread portion provided with a tread pattern of left-right asymmetry and having an outboard tread edge and an inboard tread edge,

the tread pattern comprising circumferentially continuously extending main grooves which are

an inboard shoulder main groove, an inboard crown main groove, an outboard crown main groove, and an outboard shoulder main groove, whereby

the tread portion is axially divided into

an inboard shoulder land portion between the inboard shoulder main groove and the inboard tread edge,

an inboard middle land portion between the inboard crown main groove and the inboard shoulder main groove,

a center land portion between the inboard crown main groove and the outboard crown main groove,

an outboard middle land portion between the outboard crown main groove and the outboard shoulder main groove, and

an outboard shoulder land portion between the outboard shoulder main groove and the outboard tread edge,

wherein

the width of the outboard shoulder main groove is smaller than the width of the inboard shoulder main groove,

the tread pattern further comprises bent middle axial grooves arranged circumferentially of the tire at intervals, and disposed in the inboard middle land portion but not disposed in the outboard middle land portion,

each of the bent middle axial grooves comprises:

a main portion which extends from the inboard shoulder main groove toward the tire equator, while inclining with respect to the tire axial direction to one tire circumferential direction, and

a turnback portion which extends from the main portion toward the other tire circumferential direction and terminates within the inboard middle land portion, wherein

the main portion and turnback portion are substantially straight, and intersect with each other at an acute angle,

the inboard shoulder land portion is provided with a plurality of inboard shoulder sipes arranged circumferentially of the tire at intervals, and each extending from the inboard shoulder main groove to the inboard tread edge, and

the outboard shoulder land portion is provided with an annular part and an axially inner non-grooved rib part and the rib part extending continuously and circumferentially of the tire and disposed adjacently to the outboard shoulder main groove, and

the annular part provided with a plurality of outboard shoulder sipes arranged circumferentially of the tire at intervals.

2. The pneumatic tire according to claim 1 , wherein

said turnback portion extends parallel with the tire circumferential direction.

3. The pneumatic tire according to claim 2 , wherein

the number of the inboard shoulder sipes is more than the number of the bent middle axial grooves.

4. The pneumatic tire according to claim 2 , wherein

the inboard middle land portion is provided with a plurality of inboard middle sipes arranged circumferentially of the tire at intervals, and

each of the inboard middle sipes extends axially outwardly from the inboard crown main groove and terminates within the inboard middle land portion.

5. The pneumatic tire according to claim 2 , wherein

the bent middle axial grooves have a width, and

the inboard crown main groove and the outboard crown main groove have a width more than the width of the bent middle axial grooves.

6. The pneumatic tire according to claim 1 , wherein

the number of the inboard shoulder sipes is more than the number of the bent middle axial grooves.

7. The pneumatic tire according to claim 6 , wherein

the inboard middle land portion is provided with a plurality of inboard middle sipes arranged circumferentially of the tire at intervals, and

each of the inboard middle sipes extends axially outwardly from the inboard crown main groove and terminates within the inboard middle land portion.

8. The pneumatic tire according to claim 6 , wherein

the bent middle axial grooves have a width, and

the inboard crown main groove and the outboard crown main groove have a width more than the width of the bent middle axial grooves.

9. The pneumatic tire according to claim 1 , wherein

the inboard middle land portion is provided with a plurality of inboard middle sipes arranged circumferentially of the tire at intervals, and each extending axially outwardly from the inboard crown main groove and terminates within the inboard middle land portion, and

the outboard middle land portion is provided with

a plurality of outboard middle axial grooves arranged circumferentially of the tire at intervals and each extending axially outwardly from the outboard crown main groove to terminate within the outboard middle land portion, and

a plurality of outboard middle sipes arranged circumferentially of the tire at intervals and each extending axially inwardly from the outboard shoulder main groove to terminate within the outboard middle land portion.

10. The pneumatic tire according to claim 9 , wherein

the axial outer ends of the inboard middle sipes are located axially outside the turnback portions.

11. The pneumatic tire according to claim 10 , wherein

the bent middle axial grooves have a width, and

the inboard crown main groove and the outboard crown main groove have a width more than the width of the bent middle axial grooves.

12. The pneumatic tire according to claim 9 , wherein

the bent middle axial grooves have a width, and

the inboard crown main groove and the outboard crown main groove have a width more than the width of the bent middle axial grooves.

13. The pneumatic tire according to claim 1 , wherein

the bent middle axial grooves have a width, and

the inboard crown main groove and the outboard crown main groove have a width more than the width of the bent middle axial grooves.

14. The pneumatic tire according to claim 1 , wherein

the inboard crown main groove has a width, and the outboard crown main groove has a width same as the width of the inboard crown main groove.