jk unlimited springs Front progressive springs with variable pitch for Jeep Wrangler JK Unlimited, 4 doors.They are built in Italy with high quality 52SiCrNi5 steel in compliance with the UNI EN 10089 standard, by a company certified by TÜV according to the UNI/ISO 9001:2015 standard.They are longer than the originals, reinforced with a progressive effect.From the menu above you can choose the extra length compared to the original setup, they have a soft calibration optimized to give maximum off-road performance but still perfectly suitable for road use thanks to the characteristics of the variable pitch springs.Progressive springs differ from traditional ones because they have a variable pitch, i.e. the distance between the coils is not constant but varies along its length.A progressive spring allows you to insert more coils than a traditional spring resulting much softer, and at the same time allowing the spring to progressively harden thus obtaining an extremely soft, comfortable and capable of copying the terrain but very stable on the road. The stiffness of a spring with the same material and wire diameter is precisely given by the number of coils and their pitch.The main off-road advantages of a progressive spring: increased ability to copy terrain; greater excursion for the same length compared to a traditional spring; very stable in the side passages as it stiffens when crushed; greater absorption of sudden obstacles, as by progressively stiffening it brakes a possible obstacle (boulders, roots, etc.) without reaching a buffer. The main advantages of a progressive spring on the road: very stable on fast sections; much more comfortable than a traditional spring thanks to the high number of coils; minimizes body roll when cornering as it progressively stiffens when crushed.