Pneumatic tire

1. A pneumatic tire comprising:

at least three circumferential grooves extending in a tire circumferential direction in a tread portion; and

at least four ribs defined by the at least three circumferential grooves, the at least four ribs extending in the tire circumferential direction;

at least two ribs of the at least four ribs protruding outward in a tire radial direction beyond a profile line of a tread surface when viewed in a meridian cross section, the at least two ribs being provided adjacent to one another and interposed by one of the at least three circumferential grooves; and

a protruding amount of the at least two ribs decreasing in order from a first side to a second side in a tire width direction and a difference between a maximum value and a minimum value of respective protruding amounts of the at least two of the ribs being not less than 0.4 mm and not greater than 0.8 mm;

wherein the at least two ribs include a shoulder side rib defined as an outermost rib of the at least four ribs in the tire width direction.

2. The pneumatic tire according to claim 1 , wherein the protruding amount from the profile line of the at least two ribs is from 0.05 mm to 2.0 mm, both inclusive.

3. The pneumatic tire according to claim 2 , wherein

a vehicle inner/outer side orientation when mounted on a vehicle is designated, and

the protruding amount of the at least two ribs decreases in order from the vehicle outer side to the vehicle inner side.

4. The pneumatic tire according to claim 1 , wherein

a vehicle inner/outer side orientation when mounted on a vehicle is designated, and

the protruding amount of the at least two ribs decreases in order from the vehicle outer side to the vehicle inner side.

5. The pneumatic tire according to claim 1 , wherein at least three of the at least four ribs protrude beyond the profile line, and a difference between the respective protruding amounts of the at least three ribs is 0.3 mm to 0.8 mm, both inclusive.

6. The pneumatic tire according to claim 1 , wherein each of the at least two ribs protrudes maximally at the center of the tire width direction when viewed in a meridian cross section.

7. A pneumatic tire comprising:

at least three circumferential grooves extending in a tire circumferential direction in a tread portion; and

at least four ribs defined by the at least three circumferential grooves, the at least four ribs extending in the tire circumferential direction;

at least three ribs of the at least four ribs, adjacent to one another, protruding outward in a tire radial direction beyond a profile line of a tread surface when viewed in a meridian cross section; and

a protruding amount of the at least three ribs decreasing in order from a first side to a second side in a tire width direction and a difference between the respective protruding amounts of the at least three ribs adjacent to one another is 0.3 mm to 0.8 mm, both inclusive;

wherein the at least three ribs include a shoulder side rib defined as an outermost rib of the at least four ribs in the tire width direction.

8. The pneumatic tire according to claim 7 , wherein each of at least two of the at least three ribs are provided between the circumferential grooves and protrude maximally at the center of the tire width direction when viewed in a meridian cross section.

9. The pneumatic tire according to claim 7 , wherein a protruding amount of the outermost rib of the at least three ribs in the first side of the tire width direction is a maximum protruding amount.