| 摘要 |
PURPOSE:To disperse stress concentrated on the bottom of a sipe for restraining the occurrence of cracks by providing a cylindrical expanded part limited in the bottom of a portion communicating to a main groove by a sipe and specified of the diameter, length and length extended from the bottom of the sipe. CONSTITUTION:The bottom of a sipe 5 is provided in a portion communicating to a main groove 2 with an expanded cylindrical part 6 having a diameter (d) larger than the width (t) of the sipe 5. The ratio of diameter (d) of the expanded part 6 to the width (t) of the sipe 5 falls within the range of 0.2t<=d<=3t. The length (a) of the expanded part 6 to the diameter (d) and length (b) of the sipe 5 is defined as 2d<=(a)<=(b)/3. Further, the expanded part 6 sets the relation between the depth (h) from the surface of a block 4, the length (h)-(H) extending from the depth L of the sipe 5 and the diameter (d) to 0.1d<h-H<=1.45d. When the extension length h-L is smaller than 0.1d, the deformation of the bottom of the sipe 5 cannot be restrained so that an effect of mitigating stress cannot be obtained. |
