Air ride hitches

My TrailAir has a mark on the shock that shows how much pressure to put in. It is at about the half stroke point of the shock. I can watch the bottom half of the hitch moving in the opposite direction of the lower half, so I know it is working. Pressure in the bag with my rig is right at 80PSI. Does the side of the bag feel rock hard? Yes. Is air a compressible gas? Yes again. I also have Firestone air bags on the rear axle of my truck. Going down the road, I can see the pressures bouncing all over the place with the gauge on my dash. The fact that air can be compressed is what makes these things work, period.