Technically the Swift lowering springs would be called a dual rate spring. Effectively it acts like a linear spring. The tighter wound section collapses when the car is on the ground. The purpose of that section is to provide tension so the spring would stay in place when the suspension is in full extension. Once the car sits on the ground, the other less tightly wound (main) section takes over, and any further travel from that point forward will act in a linear fashion. Without the "tender" section, the spring would not be able to lower the car that much, or would unseat itself if the suspension fully extends.