A few weeks ago, a customer of ours stopped by my house to pick up some shocks for his Jeep. He was driving his 2013 Ford E250 RB 2wd van that we had recently done considerable suspension modifications to and added all the Aluminess goodies to.
He mentioned that he had air bags installed... "What?"
I explained the following, and he called me the next day, said he couldn't sleep and kept thinking about the air bags and wanted them removed. He had wondered why the ride had seem so harsh and didn't put 2 and 2 together until we talked.
I took a few pictures:
I removed the valve core from the schrader valve so there would be no air pressure or vacuum in the bag. This picture is at ride height. There is approximately 4.75 inches between the top and bottom metal mounts of the air bag.
I disconnected the lower air bag mount from the axle tube and used a Porta Power to compress the air bag until it bottomed out internally and started to lift the van. This represented the total available Bump Travel with the air bags installed - only 2.5 inches (4.75" at ride height - 2.25 fully compressed).
You can also see from the amount of shock travel (2 inches) that the bump travel was severely restricted. Normally this shock should cycle full stroke.
Next we jacked up the van from the frame, suspending the axle and tires in the air. You can see that the air bag acted as a limit strap and the axle was hanging from the air bag and not the shock and springs. The air bag manufacture specifically warns against allowing this as they are concerned about the life of the air bag - it is not designed to hold the weight of the axle, wheels and tires. Essentially there is only ~3 inches of droop from ride height and 5.5 inches of total travel because of the air bags.
Next I disconnected the lower air bag mount from the axle and allowed the axle to fully droop out to where it is limited by the springs and shock (we strive to time these together for maximum travel). You can clearly see how much additional droop was available.
I hope you will think twice before using air bags. They have their place, but...