Pneumatic radial tires

A high performance radial pneumatic tire for a passenger car, comprising;

• a tread provided with a plurality of substantially straight circumferential grooves extending in a circumferential direction of the tire, a plurality of inclined lateral grooves across the circumferential grooves, and plural rows of land portions defined among the circumferential grooves, the lateral grooves, and both edges of the tread, wherein at least the circumferential groove to be located nearest to an axially outer side edge of the tread on a treading surface thereof when the tire is fitted to the passenger car has an axially inner wall and an axially outer wall, and said axially outer wall is inclined more greatly with respect to a normal erected on the tread surface than said axially inner wall to gradually increase a width of the groove to a surface of the tread from a position P spaced from the tread surface a distance h 10-70% of a depth H of the circumferential groove, a width of an opening of the circumferential groove to the surface of the tread is in a range of 3-18 mm, and wherein an axially inner groove wall of the circumferential groove to be located axially outside the tire with respect to an equator of the tire in the state that the tire is fitted to a vehicle is inclined to gradually increase the width of the groove from the bottom of the groove to the surface of the tread, and axially outer groove wall has a first portion which is inclined more greatly than that of said axially inner groove wall of the circumferential groove to gradually increase the width of the groove from the position spaced radially outside the bottom of the groove to the surface of the tread, and a second portion of the axially outer groove wall is inclined to gradually increase the width of the groove from the position to the bottom of the groove.