A spring is just a spring right?...WRONG. The factory used up to seven different front springs and eight different rear springs on TJs. Why so many? It's not just so that the height of every TJ from a stripped 4-cylinder soft-top to a loaded Rubicon Unlimited dual-top is the same. More importantly, it's so that they all ride and handle the same...in short, so that they have the same frequencies. No other aspect of your rig's suspension has as much direct affect on ride - and especially handling - as these frequencies. Nth Degree springs are designed the same way, even including the special benefit of a progressive-rate design: the more you load it, the stiffer it gets – keeping the frequency nearly constant. Because the relationship of the front springs to the rear is also critical to great ride and safe handling, Nth Degree springs are tuned and intended to be used together as matched F/R sets - we do not recommend they be combined with other makers' springs. As part of an Nth Degree suspension system or to replace your existing 'lift' springs, these will perform beautifully whether loaded or empty, both on-road and off.
A quote from my wife: "I don't even want to know how much it cost, I'm not in the mood to be that pissed off today."