To add to this. What I'm trying to emphasize is that air springs do a great job of "leveling", but they do NOTHING about weight transference. Things might "look great", but you can still be terribly overloaded.

And I feel there are some people who don't really understand the difference between leveling and load distribution.

I have nothing at all against leveling air springs when they're used properly.

- Jack

I'm using Firestone Bags on My '99 Chevy truck. I started with them installed alone, with an air line and valve stem on each side. Sweet ride, but it meant I had to get out my little 12v air compressor each time I hook on the trailer and fill each side. Then use a pressure gauge to get to my pressure. I figured out that I needed 32-35 psi to answer your question. I carry a lot of gear in the truck, plus the trailer on the hitch, and just went out at night and kept adding air until my headlights came back to level.
I put up with that for about a year, and decided to install an Air-Lift on-board compressor. Sweeter... The only difference is that I had to wye both bags to the compressor line. The difference is in the ride. Having both bags on the same air line means that when one side hits a bump, the other bag gets a jolt of air pressure. Not a big deal, if you spend a lot of seat time like me, but you can notice the rear suspension doesn't feel as tight. Not a big problem for the convenience...

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'89 22' FunChaser