I had a chevy truck a long time ago that had them, You could air them up and haul anything. Worked really good but you had to let the air out for just riding, it would bounce your head off the ceiling. Put a set of hellwig helper springs on my old ford i have now. The original springs were giving up over the years from all the heavy weight i hauled in it. They brought it back to life. I can load it down with red oak way up past the bed and it will ride without too much sag. They are a lot cheaper than the bags and easy to install.