| 摘要 |
PURPOSE:To improve the wear resistance at summer time and groove bottom crack resistance at winter time by setting the hardness of the inner side rubber layer of a tread part at the specified value higher than that of the outside rubber layer and forming the outside rubber layer so that the tread volume duty factor becomes at specified value by the foaming rubber of specified foaming rate. CONSTITUTION:The Shore hardness A of the inner side rubber layer 3B of a tread 3 is set at 54-80 deg. to make it higher than the hardness of the outside rubber layer 3A. The outside rubber layer 3A is formed by the foaming rubber whose foaming rate is in the range of 5-50% and the percentage occupied the volume of the tread 3 is set at >=10%. The foaming rate of the both side area 3a adjacent to the side rubber part 3D of the outside rubber layer 3A is made smaller than that of a center area 3b. By this structure the wear resistance is improved without spoiling the performance at summer time, the driving performance, etc. of winter time are improved and especially the groove bottom crack resistance performance can be improved. |
