| 摘要 |
PURPOSE:To eliminate a possibility of gripping stones or the like in grooves and to improve the cracking resistance of the tire by a method wherein the zigzag grooves arranged in a tread part is so formed that a step part having a predetermined depth and width is provided on one side wall part, and in this case the step width is decreased gradually from a circumferential rib stretching part toward a rib corner part. CONSTITUTION:The step part 13 having a height H' of a value within a range of 30'60% of the maximum groove depth H is formed on one of the side wall parts 11 and 12 of the zigzag grooves 2-5. As to the width W' of the step part 13, a groove width expansion part 16 is formed which becomes narrower continuously and gradually from the stretching part 14 of the circumferential ribs 6-10 toward the corner part 15 thereof within a width value of 20-0% of the maximum groove width W. With this construction f the tire groove, the stone gripped in the groove can easily come out. Further, the frictional wear resistance of the tread part 1 is not decreased from an initial stage of friction to a final stage, and also the cracking resistance of the tire can be much improved. |
