Pneumatic tire with tread having cutaway portions formed in center rib

A pneumatic tire comprising:

• a pair of first main grooves which are formed in the center region of a tread and extend in the tire circumferential direction;
• a pair of second main grooves which are formed respectively outward of the corresponding first main grooves and extend in the tire circumferential direction;
• a plurality of first lug grooves and a plurality of second lug grooves which are alternately arranged in the tire circumferential direction, the first lug grooves each extending from one of two shoulder ends of the tread inward in the tire-width direction and communicating with the corresponding first main groove, the second lug grooves each extending from one of the two shoulder ends of the tread inward in the tire-width direction but not communicating with the corresponding first main groove;
• a center rib which is defined between the pair of first main grooves and which extends continuously in the tire circumferential direction;
• a shoulder block row which is defined between each of the second main grooves and a corresponding one of the shoulder ends and includes a plurality of blocks;
• and
• an intermediate block row which is defined between each of the first main grooves and a corresponding one of the second main grooves and includes a plurality of blocks,
• the pneumatic tire characterized in that:
• each intermediate block row includes long blocks each of which has a tire-circumferential-direction length equivalent to the total length of each two blocks included in the corresponding shoulder block row;
• a plurality of cutaway portions are formed in the center rib at certain intervals in the tire circumferential direction,
• each cutaway portion has a triangular shape formed on a ground-contacting surface of the center rib and having an apex and a pair of end points all of which are connected to one another, and
• each cutaway portion has a three-dimensional structure such that a valley line is formed by a first contour line connecting the apex to a bottom point defined at a position located at the bottom of the groove and between the pair of end points.