| 摘要 |
PURPOSE: To improve rigidity and restrain heel-and-toe wear by setting the upper angle of a reference face formed by a reference line joining the extended face of the reference face with a tread face and a line in the circumferential direction on the acute angle edge side in a specific range, and setting the upper angle of a slope formed by an upper edge line and the line in the circumferential direction in larger specific range than that of the upper angle of the reference face. CONSTITUTION: The upper angleα1 of a reference face 10 formed by a reference line SL joining the virtual extended face of the reference face 10 with the virtual extended face of a tread face 2 and a line L in the circumferential direction on the acute angle edge side m1 is set to be 60 deg.-85 deg.. The upper angleα2 of a slope 11 formed by an upper edge line 11A and the line L is set to be larger than the upper angleα1 of the reference face 10 and in a range 65 deg.90 deg.. Because the slope 11 is provided on the acute angle edge side m1 easily being worn of the lateral wall 7B of a block 5 in this way, rigidity of the block 5 can be improved on the acute angle edge side m1 In addition, external force applied to the acute angle edge side m1 can be also reduced, and hence heel-and-toe wear can be prevented. |
