I have cartridges, and they hold air just fine. But there is only a very small amount of air involved and getting both sides the same is a touchy proposition at best. It rides much better if I have about 20 lbs in each one, I'm going to try up to 30 lbs & see what gives. That also raises the front end height about an inch. Some claim the air makes no real difference, but I find it very noticeable, especially on washboard surfaces and RR tracks.I am connecting the two so that they will automatically balance each other regardless of the actual pressure involved. Today I found barbed hose fittings that thread right onto the valve stems. A local bicycle shop knew what I needed as they had recently dug some up for a project. I can run them to a T and be good to go, but I will probably put a smallish tank inline as well.