The entire unit may also be exchanged with another unit with a different rate spring pre-installed to allow spring rate changes without affecting ride height. Spring, includes a thrust bearing set and fits most shocks. Our Spring Pre-Loader allows the ability to run a soft spring but pre-load it for higher static load · Uses a 14 tall 3 I.D. spring (spring is sold separately... The pre-loaded spring will have less rate increase as the suspension travels. Pre-Loaded allows use of a softer spring rate that is pre-loaded at ride height. Speedway Front Solid Axle Leaf Spring Perch, Plain Forged Steel ALLSTAR PERFORMANCE Leaf Spring Slider Box w/Nylon Bushings ALL60034 /in spring can be pre-loaded to 400 lbs. /in as suspension travels. Allows use of a softer spring rate that is pre-loaded at ride height Pre-loaded Spring For 14 Tall Springs Allstar Performance 64234 Spring Pre-Loader For 14" Tall Spring Coilover Spring Pre-loader The pre-loaded spring will have less rate increase as the suspension travels , Spring pre-load