4000S Coil Overs are essentially springs that are used in conjunction with shock absorbers to create your suspension system. 4000S Coil Overs can have a high spring constant for heavy or high sportier performance, or a lower spring constant for a boatier feel or a lighter car. High quality 4000S Coil Overs work with your shock absorbers to dramatically decrease the feel of bumps and also increase the grip of the tires on the roads during turns and bumps.