In the present invention, an outer tire is supported and positioned by an auxiliary inner tire such that air can be pumped into the space between the inner and outer tires. When there is a flat tire or leakage, the outer tire is supported by the inner tire and still has an appropriate support to the car, and thus the outer tire will not be compressed completely or grinded by the rim of the wheel, so that the tire will not be damaged easily and the auxiliary inner tire can continue running for a short time.