The Edelbrock Performer IAS Shock Absorber features the patented Inertia Active System. This exclusive design helps in switching instantly between a soft and a firm circuit for superior handling and a smooth ride. On smooth roads the inertia activated valve closes to give a firm ride, excellent cornering and reduced body sway. Under rough conditions, the valve opens to make the shocks softer and more responsive. The variable dampening rate improves handling as well as ride comfort. The higher dampening force is applied when it is needed to control excess chassis force and lower dampening force is applied when the wheel hits bumps, pot-holes, railroad tracks or any other surface irregularities.