This invention provides a rubber composition capable of improving a durability to heat buildup of a heavy duty pneumatic radial tire by applying to a cushion rubber of the tire to lower heat buildup of the cushion rubber without lowering a fracture strength of the cushion rubber as well as a tire using such a rubber composition and being excellent in the durability to heat buildup. The rubber composition is characterized in that 25-45 parts by mass of carbon black having a nitrogen adsorption specific surface area (N2SA) of not less than 60 m2/g as a filler is compounded based on 100 parts by mass of a rubber component comprising at least one of natural rubber and synthetic isoprene rubber, and a modulus at 50% elongation is not less than 1.1 MPa, and a loss tangent (tan δ) at 25°C and 2% strain and an amount of carbon black compounded based on 100 parts by mass of the rubber component satisfy a relation of the following equation (I): tan δ/amount of carbon black compounded≤0.0015
本发明提供了一种橡胶组合物,该组合物能够通过应用于重型充气子午线轮胎的衬垫橡胶,在不降低衬垫橡胶的断裂强度的情况下降低衬垫橡胶的热积聚,从而提高重型充气子午线轮胎的热积聚耐久性,还提供了一种使用这种橡胶组合物的轮胎,该轮胎在热积聚耐久性方面表现优异。该橡胶组合物的特征在于,以 100 份(质量份)由
天然橡胶和合成
异戊二烯橡胶中的至少一种组成的橡胶组分为基础,以 25-45 份(质量份)具有不小于 60 m2/g 的氮吸附比表面积(N2
SA)的
炭黑作为填料进行复合,且 50%伸长率时的模量不小于 1.1 MPa,且在 25°C 和 2% 应变条件下的损耗正切值(tan δ)与按 100 份橡胶组分质量计算的复配
炭黑量满足下式 (I) 的关系:tan δ/ 复配
炭黑量≤0.0015