| 摘要 |
PURPOSE:To prevent an abnormal abrasion while maintaining drainage efficiency by making the longitudinal main sub-groove larger while the branch broove shallow with such an arrangement that the space between main longitudinal grooves for partition of a block and a rib is set at more than 20% of the tread width and less than 60% of the belt layer effective width. CONSTITUTION:The space between two longitudinal main grooves 1 roughly dividing the tread width into three parts is set at 20 to 60% thereof to reduce or check shoulder abrasion. Like longitudinal sub-grooves 2 and 3, the grooves 1 are formed in a U-shape with a large width set at less than 5 to 9% of the tread width to maintain the drainage effect. The depth of branch grooves 4 is set at to less than 20% of that of the grooves 1 to avoid an irregular abrasion on the block. The pitch P of zigzags on the edge of the grooves 1 is set at 0.3 to 1.3 times as large as the width W thereof. In addition, the width a of the zigsag is set at 0.1 to 1.0 times as large as the width W. Thus, the degree of the zigsags can be lowered. With such an arrangement, abrasion can be reduced while drainage can be secured. |
