An air compressor mountable within an annular cavity of a pneumatic tire comprises an air inlet for receiving air to be pumped into the tire cavity, an air compression chamber in fluid communication with the air inlet, and an air outlet in fluid communication with the air compression chamber. Further, the compressor comprises a pressure compensation chamber in fluid communication with the tire cavity when the air compressor is mounted within the tire cavity, and a double piston having a shaft and two opposing piston ends, the shaft rigidly connecting both piston ends with each other, wherein the first piston end is arranged and movable in the compression chamber and is actuatable by hydraulic pressure between a compression state and an intake state, and wherein the second piston end is arranged and movable in the pressure compensation chamber and subject to the pressure of the tire cavity when the compressor is mounted within the tire cavity. Moreover, the present application is directed to a tire comprising the aforementioned air compressor.