FairfaxPat
Senior Retro Guru
Air springs are Rising Rate springs, that is, the spring rate curve gets steeper the more it is compressed, while standard springs have a Linear Rate, unless they are Progressively wound. As an example, if it takes 50 pounds pressure to move an air spring one inch, it is going to take much more than another 50 pounds to compress it the next inch, and so on. With a standard wound spring, however, the first inch might take 50 pounds pressure, and the second inch of travel is going to take just another 50 pounds, or 100 pounds total to go the second inch, and so on. There are Progressively wound steel springs also, they get thicker towards the bottom. Air Springs are lighter and more common, while DH bikes prefer steel for the big hits-plus weight isn't such an issue on a DH bike.