Pneumatic tire

1. A pneumatic tire comprising:

a tread portion and a belt layer on an outer periphery of a carcass layer that extends between left and right bead portions and

a plurality of circumferential main grooves extending in a tire circumferential direction provided on an outer surface of the tread portion, wherein

on a tire cavity side surface of the tread portion, a ridge (Ra) protruding into the tire cavity side in a direction opposite to a tire radial direction is formed that extends in the tire circumferential direction in a position offset from a tire center towards a well side of a mounting rim so as to encompass an entire width of a well and an entire width of a circumferential main groove positioned farthest to a shoulder side; and

an edge of the ridge (Ra) on the shoulder side in a tire width direction is positioned more towards the tire center than a point where a perpendicular line extending from an edge of a widest part of the belt layer intersects the carcass layer, and an edge of the ridge (Ra) on the tire center side extends to the tire center if there is no circumferential main groove provided on the tire center, and to a point on a side of the circumferential main groove on the tire center opposite to the well that is 15 mm removed from an edge of the circumferential main groove on the side opposite to the well if there is a circumferential main groove provided on the tire center.

2. The pneumatic tire according to claim 1 , wherein a thickness of the ridge (Ra) from an innermost layer of the carcass layer is from 1.0 to 10 mm greater than in other regions of the tire cavity side surface.

3. The pneumatic tire according to claim 1 , wherein another ridge (Rb) is formed on the side of the tire center opposite to the well extending in the tire circumferential direction and protruding into the tire cavity side in the direction opposite to the tire radial direction so as to encompass an entire width of a circumferential main groove positioned farthest to a shoulder side on the side of the tire center opposite to the well.

4. The pneumatic tire according to claim 3 , wherein a thickness of the ridge (Rb) from the innermost layer of the carcass layer is from 1.0 to 10 mm greater than other regions of the tire cavity side surface.

5. The pneumatic tire according to claim 1 , wherein tire masses on left and right sides when a tire main body is bisected at the tire center are equal.

6. The pneumatic tire according to claim 1 , wherein the ridges are formed by disposing an elastomer between an inner liner layer and the innermost layer of the carcass layer.

7. The pneumatic tire according to claim 6 , wherein a tan δ of the elastomer is 0.15 or less.

8. The pneumatic tire according to claim 6 , wherein a hardness of the elastomer is from 70 to 95.

9. The pneumatic tire according to claim 1 , wherein a thickness of the ridge (Ra) from an innermost layer of the carcass layer is from 1.2 to 8.0 mm greater than in other regions of the tire cavity side surface.

10. The pneumatic tire according to claim 6 , wherein a hardness of the elastomer is from 72 to 85.

11. The pneumatic tire according to claim 2 , wherein tire masses on left and right sides when a tire main body is bisected at the tire center are equal.

12. The pneumatic tire according to claim 3 , wherein tire masses on left and right sides when a tire main body is bisected at the tire center are equal.

13. The pneumatic tire according to claim 2 , wherein the ridges are formed by disposing an elastomer between an inner liner layer and the innermost layer of the carcass layer.

14. The pneumatic tire according to claim 3 , wherein the ridges are formed by disposing an elastomer between an inner liner layer and the innermost layer of the carcass layer.

15. The pneumatic tire according to claim 5 , wherein the ridges are formed by disposing an elastomer between an inner liner layer and the innermost layer of the carcass layer.

16. The pneumatic tire according to claim 7 , wherein a hardness of the elastomer is from 70 to 95.