The nature of compressed air. Have you ever filled a football or the tires of your bicycle from the air tube at a filling station? The air that comes from the tube is compressed air.
Compressed air is the opposite of a partial vacuum. To make a partial vacuum we remove some of the air from a closed space. To compress air we pump more air into a closed space. Hence compressed air is air that has been crowded into a space. The pressure in any space containing compressed air is greater than the pressure of the surrounding atmosphere.
The earliest rubber tires for bicycles and carriages, and even for automobiles, were of solid rubber. It was a long time before hollow rubber tires could be made to hold air that was compressed enough to support a vehicle.
It is much more comfortable to ride on compressed air than on solid rubber. If, however, the rubber tire becomes worn thin or strikes a sharp object, it may become unable to stand the pressure of the compressed air inside it. A blowout may result.