Patent ID: 8857483
Filing Date: 2014-10-14
Classification: B60C,Y10S

Abstract:
1. A studless tire comprising a tread portion having tread edges and an overall land ratio of from 0.65 to 0.75, the tread portion provided with a pair of axially inner longitudinal grooves extending continuously in the circumferential direction of the tire and disposed one on each side of the tire equator, a pair of axially outer longitudinal grooves extending continuously in the circumferential direction of the tire and disposed one between each said inner longitudinal groove and the adjacent tread edge, and a plurality of sipes disposed in each of land portions defined by the axially inner and outer longitudinal grooves, wherein a land ratio of a crown region and a land ratio of a shoulder region are each larger than a land ratio of a middle region, wherein the crown region is defined between the groove center lines of the axially inner longitudinal grooves, the middle region is defined between the groove center line of one of said axially inner longitudinal grooves and the groove center line of the adjacent axially outer longitudinal groove, and the shoulder region is defined between the groove center line of one of the axially outer longitudinal grooves and the adjacent tread edge, the land ratio of the crown region is 0.72 to 0.78, the difference in the land ratio between the crown region and the middle region is not more than 0.15, and the difference in the land ratio between the shoulder region and the middle region is not more than 0.15, wherein said crown region is provided with crown lateral grooves extending between the axially inner longitudinal grooves and arranged at intervals in the circumferential direction of the tire so as to form a crown block row of circumferentially arranged crown blocks, said middle region is provided with middle lateral grooves extending between the axially outer longitudinal groove and the axially inner longitudinal groove and arranged at intervals in the circumferential direction of the tire so as to form a middle block row of circumferentially arranged middle blocks, said shoulder region is provided with shoulder grooves extending between the axially outer longitudinal groove and the tread edge and arranged at intervals in the circumferential direction of the tire so as to form a shoulder block row of circumferentially arranged shoulder blocks, each said crown lateral groove is made up of a narrow central groove segment crossing the tire equator and having a substantially constant width, and a pair of wide lateral groove segments each extending from one of the ends of the narrow central groove segment while gradually increasing in groove width, the groove width of the narrow central groove segment measured in the tire circumferential direction is in a range of from 0.5 to 4 mm, the maximum groove width of the wide lateral groove segment is not less than two times and not more than six times the groove width of the narrow central groove segment when measured in the tire circumferential direction, the narrow central groove segment has a depth less than the depth of the wide groove segments and in a range of from 50 to 90% of the depth of the axially inner circumferential grooves, and the angle of the narrow central groove segment is more than 0 degrees and not more than 30 degrees with respect to the tire axial direction, the middle block row is provided with a narrow longitudinal groove extending continuously in the circumferential direction of the tire, the narrow longitudinal groove is a straight groove having straight and parallel circumferential edges along the entire circumference of the tire and has a groove width smaller than those of the axially inner and outer longitudinal grooves, each said shoulder block is provided with a plurality of zigzag sipes which are a closed circumstantial sipe having closed ends within the block, and axially inside of the circumferentially-extending zigzag sipe, closed axial sipes having closed ends within the block and semi-open axial sipes extending axially outwardly from the axially inner circumferential edge of the shoulder block and terminating before the circumstantial sipe, and no sipe is disposed on the axially outside of the closed circumstantial sipe.