A pneumatic tire includes a tread portion provided with a shoulder main groove and a crown main groove to form a middle land portion therebetween. The middle land portion is provided with a first middle lug groove including a first groove wall and a second groove wall, wherein the first groove wall includes a protrusion protruding toward the second groove wall on the side of the shoulder main groove. The protrusion includes a front wall located so as to form a sipe portion between the front wall and the second groove wall, a top wall, a first lateral wall located axially outward of the front wall and a second lateral wall located axially inward of the front wall. The front wall is configured to a triangular shape.

A pneumatic tire 1 is provided in the tread portion 2 with a pair of center main grooves 3 arranged on both sides of the tire equator C, and a pair of shoulder main grooves 4 arranged on both sides thereof, and is provided on both sides of the equator C with middle land portions 6 defined between the center main grooves 3 and the shoulder main grooves 4. The middle land portions 6 are provided with a plurality of middle oblique grooves 10. Each middle oblique groove 10 extends toward the tire equator C from the outer end 10o in the tire axial direction communicating with the shoulder main groove 4, and the inner end 10i terminates without reaching to the center main groove 3. In an outer end 10o side of the middle oblique groove 10, an outer shallow bottom portion 12 having a depth less than the maximum depth of the middle tilted groove 10 is provided.

The present invention provides a pneumatic tire which is sufficiently reduced in the rolling resistance during high-speed travel, while having sufficiently improved chipping resistance. A pneumatic tire which has a tread part, wherein: at least one rubber layer that forms the tread part contains a rubber component that contains an isoprene rubber, a styrene butadiene rubber and a butadiene rubber, while containing more than 5 parts by mass but 25 parts by mass or less of carbon black relative to 100 parts by mass of the rubber component; and if Wt (mm) is the cross-sectional width of the tire, Dt (mm) is the outer diameter of the tire, and V (mm.sup.3) is the virtual volume that is the volume of the space occupied by the tire when this pneumatic tire is installed on a standardized rim and the internal pressure is 250 kPa, (formula 1) and (formula 2) are satisfied.
1700(Dt.sup.2/4)/Wt2827.4(formula 1)
[(V+1.510.sup.7)/Wt]2.8810.sup.5(formula 2)

The pneumatic tire has a tread pattern including a plurality of ribs partitioned by shoulder primary grooves and a center primary groove. An axial groove which extends in a tire axial direction is formed on the rib, and the axial groove includes a point of inflection and is connected to at least one of the shoulder primary groove and the center primary groove. A notch having a triangular shape and which opens to the center primary groove is provided on the rib, at a center part of a block separated by the center primary groove and the axial groove. The center primary groove has a plurality of groove-bottom protrusions formed intermittently in a tire circumferential direction. The groove-bottom protrusion is longer in the tire circumferential direction than in the tire axial direction, and all or a part of the plurality of groove-bottom protrusions exists at a position opposing the notch.