Carli progressive-rate Add-A-Pack rear springs are specifically designed to address the harsh rebound of the factory overload spring they replace. When used in conjunction with a Carli Suspension System, they effectively mitigate the impact of medium to large bumps. By replacing the lower overload springs, which are typically one inch thick and do not follow the contour of the rest of the pack, with a mini progressive six-leaf pack, the overall capacity of the truck remains unchanged as determined by the factory springs. However, the progression of the rear spring rate becomes significantly more predictable.This modification results in a smoother engagement and disengagement of the spring, thereby improving both ride quality and traction.