Patent ID: 7178570

Claim:
A pneumatic tire comprising a tread portion provided with circumferential grooves, main oblique grooves and auxiliary oblique grooves, the circumferential grooves including a pair of axially outer grooves disposed one on each side of the tire equator and at least one axially inner groove between the axially outer grooves, so as to divide the tread portion into at least four circumferential regions including a pair of axially inner regions between the axially outer grooves and said at least one axially inner groove and a pair of axially outer regions axially outside the axially outer grooves, the main oblique grooves each extending across one of the axially inner regions so that the axially outer end is connected with the adjacent axially outer circumferential groove and the axially inner end is connected with the adjacent axially inner groove, the auxiliary oblique grooves arranged alternately with the main oblique grooves in the circumferential direction of the tire, and each said auxiliary oblique groove extending axially inwardly from the adjacent axially outer circumferential groove, while inclining towards the same circumferential direction as the main oblique grooves, to one of the axially adjacent main oblique grooves, whereby the auxiliary oblique groove is connected to said adjacent axially outer circumferential groove and said one of the axially adjacent main oblique grooves only, each said auxiliary oblique groove comprising a narrow middle portion having a groove width of more than 0.5 mm and not more than 3.0 mm and a wide end portion connecting to said one of the axially adjacent main oblique grooves while gradually increasing the width of the wide end portion from the narrow middle portion, the axially inner regions each having an axial width Ll of from 0.15 to 0.25 times the critical tread width Tw 1 , and the main oblique grooves each having an inclination angle θ 1 of from 45 to 90 degrees at the axially outer end thereof, and an inclination angle θ 2 at the axially inner end thereof which is less than the inclination angle θ 1 , when measured with respect to the tire circumferential direction.