This rear suspension upgrade from Timbren SES fits Ford F-250 and F-350 pickup trucks and chassis cabs. Each laser-cut steel piece is precision bent and powder coated to ensure a quality fit.Timbren engineered hollow rubber springs to deliver a progressive spring rate meaning the harder the weight pushes down, the harder they work to prevent rear end sag. Whether you’re towing a trailer or hauling a heavy load in the bed, the rubber springs adjust automatically to keep the vehicle level at all times. The upgrade replaces the frame’s jounce stop. Its unique design provides superb ride quality – loaded or unloaded. Unlike other auxiliary spring systems, this upgrade guarantees the best of both worlds – maximum stability yet still a comfortable ride when unloaded.Timbren recommends this Severe Service kit for slide in campers or salt spreaders – anywhere extra stability is needed (reducing roll and sway) while rated at 8000 pound capacity. However, this does not increase the Gross Vehicle Weight Rating set by the manufacturer, so do not exceed it.