PURPOSE: To decrease occurrence of counter-bored abrasion by constituting a tread part in a right and left unsymmetrical structure consisting of an installation outside part of narrow tread half breadth and an installation inside part of wide tread half breadth against a sectional center line and specifying a ratio of the breadths of the installation outside part and the installation inside part.

CONSTITUTION: A carcass layer 1 and a belt layer 2 are almost arranged symmetrically against a sectional center line CL orthogonal with a tire rotary shaft. In a pneumatic radial tire, a tread part 3 set outside in the tyre radial direction of the belt layer 2 consists of an installation outside part 3a with a relatively narrow tread shaft breadth WO and an installation inside part 3b with a relatively wide tread half breadth WI against the sectional center line CL and it is constituted in a right and left cymmetrical structure. Subsequently, a ratio WI/WO between the breadth WO of the installation outside part and the breadth WI of the installation inside part is set as 1.05-1.3. Consequently, it is possible to improve grounding property, persistence against sideway slide and gripping property as well as decrease occurrence of counter-bored abrasion.