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Leaf Springs Technical - Don't Leave LeavesSpring Over, Under, Or A Little Of Both... Which Can Work For You? Find out in From the February, 2009 issue of 4Wheel & Off-Road By Fred Williams Photography by Fred Williams, Harry J. Wagner, The 4-Wheel & Off-Road Archives
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Everywhere we look these days people are spending big bucks to pull the leaf springs out from under their 4x4s and swap in some high-dollar coilovers, airbags, or air shocks. But don't feel like you have to go into debt and follow this expensive trend. Leaf springs are probably the most simplistic and inexpensive suspension system for your 4x4, but even so, there are still numerous options for how to configure these packs of spring steel to perform under your vehicle. Most new leaf-sprung 4x4s come with their leaves on top of the axletubes, but over the years they could be found over or under or a combination of the two. So which setup is best for your type of four-wheeling? And is it really as cheap and easy as everyone claims to swap the springs from under to over the axles?  Most older Jeeps, Suzuki Samurais,...  Most older Jeeps, Suzuki Samurais, and Land Cruisers came stock with the leaf springs under the axletubes. For years the aftermarket options for suspension lifts involved longer shackles or longer leaf springs with a greater arch that were installed under the axletubes. This Suzuki runs with stock springs and longer shackles, but the articulation is pretty dismal, requiring some sort of locking differential to continue forward motion when the little tires are grabbing at air.  However, that same little...  However, that same little white Suzuki had little to no spring hop when clawing up a loose hill or accelerating. Even with its short wheelbase this truck felt more stable at speed than its spring-over counterpart. The benefit of a spring-under setup is the stability and lower center of gravity.  This truck was built for high-speed...  This truck was built for high-speed desert romping with the goal of being as low as possible so a custom leaf pack was mounted under the axle. Notice the lack of a traction bar commonly found on spring-over rearends since the spring-under design helps counter axlewrap. However, this same design diminishes the rockcrawling ability of the truck by reducing rear articulation and ground clearance.  Swapping from spring-under...  Swapping from spring-under to spring-over is not a simple cut-and-paste maneuver. The springs need new perches welded to the axletube, and on thin wall housing such as this Suzuki unit, care must be taken to not warp the tube. Plus, the caster angles of the knuckles are important to proper steering and must be kept leaned between 5 and 10 degrees back, which can become an obstacle when trying to also get optimum driveline angles. Along the lines of driveshaft issues, this Suzuki spring-over kit includes spacer pucks to lengthen the shafts. An even better option is to get the driveshafts lengthened with new tube.  In the front are also steering...  In the front are also steering clearance and geometry issues when going spring-over. Having a long flat drag link is a great way to counter bumpsteer, but with the springs mounted above the axletube it begins to get tight, especially with very flat springs. However there are many aftermarket high-steering arm options available such as on this front Dana 60.  Another concern with spring-over...  Another concern with spring-over is when lift blocks are installed between the leaves and the axletube. We have seen lift blocks break, fall out, and severely twist leaf springs. The biggest issue with lift blocks is that they add tremendous leverage to the leaf springs, and do not enhance the ride or performance of the suspension. Plus, lift blocks almost guarantee the need for some traction bars. Finally, we are not fans of lift blocks used under leaf springs on a front axle, as the added stresses of steering can make for a deadly combo.  Here you can see the excellent...  Here you can see the excellent ground clearance attributes of a spring-over axle suspension. Notice the required antiwrap bar to keep the leverage of the tires and gearing from twisting up the springs. On a side note, when designing your antiwrap bar, keep in mind that it can be mounted close to the differential to somewhat protect the driveshaft.  Here is another option: Run...  Here is another option: Run the front springs over the axle and the rear springs under the axle like this Toyota project. We found that in doing so we didn't need to fabricate any sort of traction bar, and the truck is very stable on side hills as well as having very limited wheelhop.  The front suspension uses...  The front suspension uses very flat leaves on top of the axles so they can flex very well, offering more articulation than the rear. Unfortunately the rear leaves get serious abuse from trail obstacles and at times become such rock anchors that certain lines are impossible. Plus the rear springs have so much arch that though they flex alright, they are definitely not as twisty as an equal length, flatter spring mounted on top would be. In addition, the front springs must be redone for a bit more curve and lift than originally designed since their arch deteriorated after use, which is more common with a flatter spring than with a stiffer, deeply arched spring pack. Verdict?
* Spring-under
* Lower center of gravity than spring-over 4x4 of equal lift
* Stiffer ride and less flex than spring-over
* Counters axlewrap
Spring-over
* Slightly higher center of gravity than spring-under 4x4 of equal lift
* Allows more flexible flatter springs for equal lift
* Can require some antiwrap bar
* Can interfere with steering
* Can require axle to be modified for proper caster
* Can require new driveshafts
* Swapping to spring-over can be more complicated than off-the-shelf bolt-on spring-under lift, but can also be cheaper if done by a qualified home fabricator
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