[jeromio]

The hydraulic over spring lets you adjust ride height, but not spring rate. Air springs *can* do both, but the spring rate adjustment adds height, which is not typically what you want. Yes, the shock rate will always be the same, but that is also not generally dependent on change in ride height (provided the shock has the travel on the upper and lower end of height).

There are systems that do air over spring, with the aired out spring being the "default" and you air up to go over obstacles (eg lowered car not being able to make it over speed bumps). I'm talking about something similar, but with air over air. In my imagination, this allows for much more flexibility. With 2 springs at "medium" inflation, you could be at optimal ride height. But you could swing the pressures across the 2 bags and gain or lose compliance without drastically affecting ride height. Or you could navigate a nasty dirt road without dragging your longtubes in the gravel.

True, it is more complex: twice the number of bags, valves and pressure sensors. I don't think the stacked bags would be any more prone to "folding" than a dual bellows spring. Attaching the 2 springs together is not that difficult a problem. The main problem is sourcing the correct short air bags w/ the appropriate load handing and then ensuring there's enough room in the cavity for the taller spring. Shortest springs I've found are min 3" though....