STUDLESS TIRE RUBBER COMPOSITION AND STUDLESS TIRE USING SAME

To achieve a studless tire rubber composition that suppresses retardation of vulcanization and can improve on-ice performance while maintaining breaking strength, the present invention includes: at least 20 parts by mass of an inorganic filler per 100 parts by mass of a diene rubber that includes at least 30 parts by mass of a polybutadiene rubber; and, relative to the inorganic filler, 10-40 mass% of basic magnesium sulfate inorganic fibers that have an average diameter of less than 1 [mu]m. 在本发明中，为了获得能够抑制硫化速度的延迟、维持断裂强度、同时使冰上性能提高的无钉轮胎用橡胶组合物，相对于包含聚丁二烯橡胶30质量份以上的二烯系橡胶100质量份，混配了无机填充剂20质量份以上，并且混配了相对于上述无机填充剂为10～40质量％的平均直径小于1μm的碱式硫酸镁无机纤维。