The Carli +3500 lbs XXHD Progressive Leaf Spring Kit is a heavy‑duty rear suspension upgrade engineered for 2019 and newer Ram 3500 4×4 Diesel trucks with a 4.25″ axle tube that regularly carry very heavy constant loads (around 3,500 lbs) such as large cab‑over campers, heavy gear, or work equipment. These progressive leaf springsprovide a 1″ rear lift while supporting substantial weight and helping maintain proper ride height and suspension geometry under load — ideal for long‑haul overland builds or serious payload applications.  

Unlike standard spring packs, the XXHD design features significantly higher spring rates tailored for heavy loads, so the truck sits at its intended height when loaded and delivers better stability and control under heavy weight. These springs are not intended to run unloaded; they are built to perform best when the intended heavy load is in place. For optimal ride quality and suspension control with these heavier springs, pairing them with 2.5″ remote reservoir shocks and custom tuning is recommended.

Key Benefits

• Designed for constant heavy rear loads (~3,500 lbs) without excessive sag 

• Provides a 1″ rear lift for balanced stance and improved rear geometry 

• Progressive spring rates enhance load carrying performance and rear control 

• Ideal for trucks with large campers or work gear setups 

• Works best with remote reservoir shocks and custom tuning for optimal ride quality

Fitment

• 2019+ Ram 3500 4×4 Diesel with 4.25″ axle tube

• Not compatible with trucks that have factory air‑assist suspension