My bus has a factory fitted spare behind the front bumper. Look at my thread "Heavy Fuel" in the bus conversions section. Look for the small black dot between the headlights. That's the portal for the tool to lower the spare from the rack under the frame. As far as using the air from the air brake system, I would recommend using a 15 gallon air tank to slave into the system before trying to change the tire. There are many different ways to accomplish this. My preferred way with my bus is to hook the slave tank into the service line via the air fitting portals by the fuel nozzle. My bus has many different advantages other buses do not have. Just an FYI. Other buses may need modifications in order to accomplish the same things my bus can do.
Firearms stand next in importance to the Constitution itself. They are the American people’s liberty teeth and keystone under independence. — George Washington