The 2.5" lift kit for the Jeep Wrangler TJ, Unlimited by Rough Country includes progressive rate front & rear coil springs. The new progressive rate coil springs are the key to giving a lifted Jeep a great ride without compromising stability. This functionality is accomplished by designing the first few coils to compress at 115 lbs per inch and progress to 160 lbs per inch during further compression. The first inch of compression reacts to smaller bumps common with on-road driving and the progressive qualities of the spring react when further compression is required. Longer shocks required and sold separately.