Superlift now offers a 4" lift system, in both fixed-link (Standard) and Rockrunner swivel link versions. Both link styles utilize factory type, steel encased rubber link eye bushings at the upper (uni-body) ends. The XJ has a uni-body chassis that exhibits quite a bit of flex. In light of this extraordinary chassis flexibility, owners that go four-wheeling frequently will prefer rubber bushed links since they transmit less driveline vibration, have a longer service life and are less "squeak prone" than links that utilize Urethane bushings throughout.