Spring-over conversions aren't exactly new to four-wheelers, but this type of suspension has never achieved anywhere near the cult status of the ubiquitous 4-inch lift kit. For many people, it seems to be strangely intimidating. Everyone knows it's simply a matter of moving the leaf springs from the bottom of the axle to the top, but since there aren't a lot of manufacturers making bolt-on kits for this type of suspension, four-wheelers tend to be uncertain about the advantages and disadvantages involved.
The primary advantages to using a spring-over setup on your trail rig are two-fold. First, you gain an immediate 5 inches of lift (minimum), which for most rigs means much greater ground clearance and the ability to bolt on those 35-inch tires without much difficulty. Of course, more lift can be gained if you choose to use lifted spring packs with greater arch, but that will greatly impact the second advantage of using a spring-over setup: ride quality. Generally speaking, the flatter the springs, the better the ride quality will be. It's no mistake that OE manufacturers have used nearly flat springs on their trucks for the past 80 years. The more arch you build into the spring pack, the stiffer it will be. Since the amount of lift that you gain with a spring-over suspension comes from lifting the entire spring pack rather than from the amount of arch in the springs, you can use flatter, softer springs for a more supple ride and flexier articulation. And if you choose to use your stock springs, then the ride quality will certainly be no worse after the conversion than it was beforehand (which is not always the case with standard lift kits).
The disadvantages to tackling a spring-over conversion are also two-fold. First, there is some tricky welding on the axles that has to be done to get the new brackets positioned correctly. Specifically, front and rear caster have to be calculated correctly in order to avoid steering problems and excessive driveshaft vibration. In some instances, the knuckles (or balls) are cut off the axles, the axles are rotated, and the knuckles (or balls) are then welded back on. So if welding and driveline geometry are not your specialty, you would be well advised to have a pro take care of this for you.
The second disadvantage to the spring-over setup is probably the one four-wheelers have heard the most about: axle wrap. Although most notable when big-horsepower motors and heavy-footed driving are involved, this is something that all spring-over setups contend with. However, there are ways to deal with it. OE manufacturers have customarily used ladder bars to eliminate axle wrap, and they have been very successful with it. We've seen modified ladder bars used on trail rigs, as well as triangulated upper A-arms, modified control arms, and radius arms. Rubicon Express sells SOA spring perches that incorporate a large, flat bar that sits at the top of the axle housing to better anchor the axle against the springs and so control axle wrap. So if this single worry has made you leery of going to a spring-over conversion, put your mind at ease. It can be dealt with.