Set of 2. Includes adapter and two shims. Swift assist springs provide a dynamic step linear rate. Like helper springs, the assist springs are designed to be fully compressed at static height. Every Swift assist spring compresses to the exact same height. This allows drivers to change assist springs without resetting the perch on the coilovers so the ride height isn't affected. Heavier rates of assist springs over helper springs are used to fine tune the rebound travel of the shock. These springs can also help preventing loss of traction due to inside wheel lift during hard cornering.