Air Springs are suspension springs that use a column of compressed air inside a flexible bellows or sleeve to support the vehicle instead of a steel coil. Because pressure and volume set the rate, an air spring is naturally progressive and its ride height can be changed on demand by adding or releasing air. That adjustability is their main advantage; the trade-offs are a rate that varies with load and temperature, added system complexity in the compressor, lines and valves, and a rate curve that is harder to characterize than a linear steel spring. Competition setups generally favor steel springs because a known, repeatable rate is the basis of predictable tuning.