PURPOSE: To enable to make an extent of supervulcanization at a position other than the latest vulcanizing point small and to curtail overall vulcanizing time, by vulcanizing a raw tire after the raw tire has been formed by allotting treat rubber in a plurality of layers which is the more it becomes inward, the faster a vulcanizing speed becomes.
CONSTITUTION: The whole thickness B of a tread part 2 is larger than the other part, for example, the whole thickness C of a slide wall part 3 by a large margin. Moreover, as an inner tread rubber 8 is positioned at the center of the direction of a thickness of the thick tread part 2, an increase of the temperature is slower drastically than that of the other part. As a vulcanizing speed of the inner layer tread rubber 8 is made faster than the vulcanizing speed of outer layer tread rubber 9, time required until the inner layer tread rubber 8 becomes the most suitable degree of vulcanization is about indentical with that of the other part or approaches to that. As basic ingredients of both the rubber 8, 9 are identical with each other, physical propeties of both the rubber 8, 9 after vulcanization, for erample, resistance to wear (Shore A handness) becomes practically identical with each other; consequently, generation of the situation such as separation is prevented.
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