Disclosed is a tire/wheel assembly allowed to still further enhance run-flat durability thereof with a simple configuration. A tire/wheel assembly of the present invention is a tire/wheel assembly where a run-flat support member inserted, coaxially with a rim, in a cavity portion of a pneumatic tire. The tire/wheel assembly is formed of a configuration where a retention groove for lubricant on an inner peripheral surface of the pneumatic tire is provided in a manner that the retention groove is faced at least to an apex of the run-flat support member.