RS5000X Gas Shock, The core of this new and innovative shock from Rancho is the unique and patented rebound valving system and an advanced compression phase of the shock absorber. This proprietary process developed by the ride engineers at Rancho will elevate the overall handling and performance of your vehicle on and off-road. Each RS5000X shock is gas pressurized to 150 PSI.* The twin tube, gas pressurized shock has a variety of advantages including minimizing air-to-oil mixture that can cause foaming and shock fade. Gas pressurization also provides a mild boost of spring rate to the vehicle. The RS5000X series features a 2-1/4-inch diameter shock body. A larger shock body allows for increased fluid capacity to operate cooler and to increase vehicle control and performance at varying speeds and terrains. The RS5000X series combines a larger shock body with all-weather fluid, allowing the shock to withstand internal temperatures between -40 and 248 degrees Fahrenheit. The Rancho RS5000X series design includes patented progressive rebound and compression discs. At lower speeds or in the earlier stages of the shock's travel, an eccentric disc in the valve shim stacks will engage the valving at lower frequencies, helping to control the energy of motion as the cycle of the shock increases or decreases in its action. When hitting a pothole, off-road trail obstacle or similar activity, Rancho's Progressive Engagement Valving allows for early flow of fluid, helping to reduce harsh initial impacts and to control the flow of fluid in a progressive, gradual manner through the valving. During on- or off-road driving activities like washboarding or when travelling a rough fire road, the early flow of fluid helps to minimize a "rough" ride as the piston movement is able to glide through the initial travel motion of the shock with minimal ground impact or force. If needed, the Progressive Engagement Valving will further engage to maintain control and stability. This fits F250 Super Duty 4WD excluding Chassis Cab