High modulus low hysteresis rubber compound for pneumatic tires

A pneumatic tire having run flat properties imparted by at least one structural component having high compressive flex fatigue, high modulus and low hysteresis sulfur-vulcanizable rubber compound, capable of being worked prior to vulcanization, and having high modulus, low hysteresis properties subsequent to vulcanization comprising:

• 100 parts by weight of an uncured grafted rubber copolymer containing,
• from about 25 to 55 parts by weight of polyisoprene,
• from about 75 to 45 parts by weight of a diene polymer selected from the group consisting of homopolymers of conjugated diene monomers and copolymers thereof with monoolefin monomers and EPDM terpolymers, to total 100 parts by weight of said grafted rubber copolymer,
• wherein a portion of at least one of said polyisoprene and said diene polymers is grafted with a polymeric metal salt of an .alpha., .beta.-ethylenically unsaturated carboxylic acid to form said uncured grafted rubber copolymer;
• about 50 to 70 parts by weight of a reinforcing filler, per 100 parts by weight of said grafted rubber copolymer;
• and
• at least about 4 parts by weight of a curative selected from the group consisting of sulfur and sulfur donors, per 100 parts by weight of said grafted rubber copolymer;
• wherein the sulfur-vulcanizable rubber compound is devoid of peroxide components.