To provide a run flat tire assembly which improves the mounting workability of a support ring, while principally providing a circumferential groove communicating to a valve port of an air valve and continuously extends in a tire circumferential direction, and a ventilation hole communicating to the circumferential groove at one end and opening to a tire cavity at the other end, on an inner peripheral surface of the support ring; and the support ring used for the same.

The run flat tire assembly includes a pneumatic tire 2; a wheel rim 3 to which the pneumatic tire 2 is equipped; and an annular support ring 4 equipped to a body 3A of the wheel rim 3, and abutting on the inner surface 2i of a tread 2a of the pneumatic tire 2 to support a load when tire inner pressure is lowered. The air vale V is mounted to the body 3A of the wheel rim 3. The support ring 4 includes the circumferential groove 18 communicating to the valve port Va of the air valve V and continuously extending in the tire circumferential direction, and the ventilation hole 19 communicating to the circumferential groove 18 at one end and opening to the tire cavity 2g at the other end, on the inner peripheral surface 4i turning to the body 3A.