We advise 0 (Zero) Preload on our kits. 

The way to determine 0 preload is to have the kit installed on the vehicle and then put the vehicle on a jack or a lift so the suspension hangs freely. From there you will want to use the Spring Perch and Locking Collar to tighten the spring to a point where there is no up or down movement but you can still turn the spring left and right fairly easily. If the spring is difficult to turn or can't turn at all it's adjusted too tight, but if you have any up or down movement on the spring, it is too loose. As all of our coilovers are designed to run at zero preload, if there is preload, or the other way around - negative preload, it will cause the shock to sit weird in the bearing/spring perch, so when you are turning it will make a metal clunk type noise. Also, once you have your kit at 0 Preload you will not need to adjust the springs for anything else.