Like a torsion trailer axle or Hendrickson suspension on a semi-truck, Sulastic Rubber Springs are a cast hinge embedded with rubber and they do settle the empty ride down considerably. I have a clothes rod attached to the hanger hooks in my SuperCab which will often bounce until it falls down when no clothes are on it and my F250 is empty. After adding Sulastic, the clothes rod stays put. The F250 vibrates less. Sulastic puts tension control on your leaf spring, taking some of the impact out of the spring action. They are made of vulcanized steel and compound rubber which take the vibration out of your trucks suspension for you and to increase the life span of your trucks suspension (leafs, shocks and brakes.)