Tires help get power to the ground, and without the right set, it’s possible to sit in an infinite burnout and not go anywhere. But what many don’t understand is that the proper suspension setup is much more important than the right set of shoes.
If the tires can’t make effective contact with the terrain then they won’t get you anywhere. Getting the power down (traction on the terrain) is one important thing, ride comfort and safety are others altogether. When picking your suspension setup, all three need to be taken into consideration. Most off-road capable vehicles nowadays see much more time on the street than they do on the dirt, so you’ll need to consider how much comfort and performance you’re willing to sacrifice on either terrain in the interest of building a vehicle that best meets all of your specific needs. There is not a perfect suspension design that does all things perfectly: It’s a give-and-take situation. But that doesn’t mean you can’t have a great riding and performing rig both on and off the highway.
Multiple suspension designs exist, and they all offer certain qualities that make them better for one situation vs. another. So to properly set up your rig, you’ll first need to know what’s out there, how they work, what they do well, and what they don’t do well. From there you can decide what suspension set up is best for you and how to modify it to better suit your exact needs.
Henry Ford used solid axles for his Model T as far back as the early 1920s. They were done differently than today with a transversely mounted leaf spring (simply put, a single sideways mounted leaf spring). Obviously, it’s no longer a new design as it’s been around for almost a century, having gone through multiple rounds of upgrades and tweaks since inception, but they work great off-road, and even with the decent amount of bump steer they come with, they do fairly well on-road as well. Plus, they can handle substantially more weight with fewer problems than other designs. This is why we see solid axles under most SUVs and every sized truck. However, suspension systems for solid axles are many, and they all have their own strengths and weaknesses, as well as their individual ways of modifying them for the dirt.
Leaf Sprung Suspension
Factory leaf-sprung rear end on a 2014 Ford Super Duty. The main two leafs locate the axle and handle basic operation spring duties; the upper and lower springs are overloads and only come into play when the vehicle is carrying a heavy load.
By far the simplest design and cheapest to modify. Leaf springs are just multiple pieces of spring steel (a steel with memory that returns to its original shape after being deformed) stacked in varying widths (rates) or amounts of leafs depending on the need. The axle is mounted to the center of the leaf (in most situations) and the frame secures both eyelets of the spring, one solid mounted and the other with a shackle to allow for suspension travel. Stock leafs generally have a main pack which allows for a pleasant ride during normal, unloaded daily driving. Below that spring (and sometimes above it) is an overload spring that takes over when the vehicle is loaded. It’s a much more robust spring designed to only come into play when the rig has a large load on/in it.
Lifting with a leaf sprung suspension is simple; in the rear, blocks can be used which simply put a spacer in the suspension, raising the vehicle by whatever thickness the spacer is although these blocks will create added axle wrap under acceleration, wearing out driveshaft components or worse. So, the use of blocks should be kept to just a few inches in lift, anything higher and you should consider getting new leafs made, adding a leaf to your existing pack, or having your existing leafs reached by a qualified shop. Adding blocks will give you a stock-like ride with stock-like performance with the benefit of larger tires; adding a leaf will make the ride stiffer, and for the most part will just add more room for tires; re-arching the leafs will generally make the ride stiffer, and again, only add room for more tires. Getting new leafs made will make the ride just about whatever you want it to be.
Lifting or modifying a front leaf sprung rig should only be done with new leafs or with parts designed specifically for the front of a leaf sprung vehicle. Blocks are not a good idea up front. There’s just too much of a rotational load on the front end to make them safe at all.
Drawbacks to leaf sprung solid axles are mainly a lack of “tuneability” when compared to 4 link setups (see 4-Link Section). Axle wrap is also a concern, but can be taken care of with a set of traction bars fairly easily.
Pure Performance’s 4-Link design for later model Ford Super Dutys uses a bracket mounted to the factory radius arm mount which gives the new 4-links a place to mount to the truck. Spring duties are then taken care of by coils in this instance, with a large reservoir shock controlling it all.
Ram trucks use this radius arm suspension design. It’s very similar to 4-link designs except caster will change as the suspension cycles. Carli Suspension’s radius arm setup for the Ford Super Duty includes new arm mounts, coil springs, reservoir shocks, radius arms, a steering stabilizer and more. This is one of the higher end suspension systems out there. This is where it gets interesting. 4 links, 3 links, radius arm and triangulated link setups are the ultimate way to tune your rig’s suspension. A link suspension, similar to those found under late model Jeep Wranglers, Rams, and Ford Super Dutys, consist of multiple solid arms, which connect the axle to the vehicle with some sort of pivoting joint. The axle then can move freely with little restriction within the limits that the links set. The solid links will also keep the axle aligned exactly how you want it to be, at any point in the suspensions travel, no matter the engine load. Springs (air, coils, coilovers, hydraulic arms, etc) of any type are then used to keep the vehicle at ride height.
Due to the solid links and free choice of shock and spring combos this type of suspension is the most tune-able for any terrain or situation. With the right knowledge, it can literally be set up to do just about anything. Adjusting things like the angle and/or the length of each link will affect how the vehicle reacts to acceleration, braking, turning, size of terrain, high-speed performance, and low speed performance, etc. If you’ve ever seen an off-road racing Trophy Truck take off from a stop and hit a turn at high speed, you would have noticed the excessive lifting and rolling of the vehicle during both situations. They were not designed to take corners well at all. But, this is an aspect designed and tuned into the suspension. Those trucks are made to travel at very high speeds through desert terrain that often includes sections of “whoops” (large repetitive bumps in the road) that are commonly over a few feet tall. The suspension is designed to move quickly to keep the tires on the ground as much as possible, maximizing driver control. And the rear link setup is usually designed more to load the rear tires allowing for maximum rear end traction. A rock buggy would have a totally different set of link geometry to help it claw its way over large boulders. These are the two extremes. Most link setups are designed to be somewhere in between.
For most of us, we’re just fine with a small lift kit to gain clearance for both larger tires, as well as whatever objects the terrain has to throw at us. Those lifts range from simple coil spring spacers adding a couple of inches to more involved kits that come with slightly longer links and new coil springs, possibly coilovers. From there, you’ll start getting into long arm suspensions that relocate the factory link mounting points and use much longer links to achieve extra travel while keeping wheel alignment angles correct throughout the range of travel. A coilover would then be the most common type of shock/spring to be used.
Ford designed the beam suspension design. It was a revolutionary design when it was released. Modifying involves drop down brackets and springs for light to medium off road use. All out race systems use new, longer i-beams and radius arms as well as coilover shocks.
Ford’s Twin Beam (I-Beam for 2WD, Twin Traction Beam for 4WD) suspension is a true HD truck suspension and was available in Rangers, Broncos, E-Vans, and F-Series trucks. It was originally designed to reduce bump steer in vehicles which had previously used a solid axle, 2WD or 4WD. It’s a sort of happy medium between a full solid axle (which handles heavy loads extremely well and works well on the dirt) and A-Arm suspension (which handles great on the road, but not as well with heavy loads or in off road situations). Currently, no late model vehicles sold after 2014 use this suspension design; the 2WD E-Vans were the last ones in production.
The Twin Beam can be best thought of as a single “L” frame: The bend in the “L” is where the wheel mounts and the other two sides which are pivot points that are mounted with bushings to different parts of the frame. One pivot basically is secured under the motor mount on either side, and the other under the passenger and driver doors respectively. By making either of the two sides longer, the amount of usable wheel travel can be increased upwards of 30 inches of travel or more. Coil springs are the most common way of suspending the vehicle here. The most common way of achieving a mid range suspension that can perform well on either terrain is with a set of drop brackets and matching coil springs to gain lift and a bit of wheel travel. Any more than that, you’re looking at coilovers with custom mounts as well as longer I-Beams and the adjoining radius arm.
Twin Beam suspensions are a favorite of high-speed desert racers due to the ease of getting huge amounts of wheel travel out of them at lesser cost than with A-arm designs. Plus, since they were originally designed to handle very heavy loads, the steering and other parts are built robustly enough from the factory to handle harsh desert terrain at very high speeds. Drawbacks from this type of suspension design include uneven tire wear and unstable camber throughout the suspension’s range of travel.
Double Wishbone Suspension
Double wishbone systems, also known as A-arm suspension is the best of all designs on the street, but lack slightly in the dirt (in stock form).
The Double Wishbone Suspension (aka A-arm) design was and is a total departure from straight axle thought and is actually a bit closer to a link setup in theory. While the Twin Beam style looked to reduce bump steer from the solid axle design, A-arm suspension takes it a step further by completely isolating the wheel and tire while keeping its travel perfectly (when designed correctly) aligned to the road, maximizing driver comfort and control.
Utilizing a dual set of wishbones (often called A-arms or control arms) and a steering knuckle in which the wheel is secured, this suspension type keeps the wheel aligned almost perfectly throughout its range of travel. Therefore, it allows for extremely good on-road manners, but not as much off road in stock trim. The dual A-Arms are generally parallel, so when the wheel moves over the bumps, the angle of the wheel and tire stays the same and therefore steers straight whether at full droop or full compression. Spring types are all over the board here. Torsion springs are the late model favorite although coil springs and struts are also in the mix from the OEMs.
The aftermarket offers steering knuckles that will allow a small 1-3-inch lift while keeping stock ride. There’s also a whole slew of coil and strut spacers, as well as torsion bar keys that will also allow for just a few inches of lift with minimal effect on ride quality. For even more ground clearance, kits generally end up relying on drop down brackets which take the mounting points for the control arms and move them down to achieve the lift. The sky is the limit there. 16-inches of lift or even more is entirely possible.
For high-performance, long-travel suspension set ups, new longer control arms and custom spindles are the norm. Stock springs will be ditched and replaced with coilovers in most cases. 12-inches of travel and 6 inches of lift is a common occurrence here. Just know that these types of kits are closer to “race only” designs –on road performance will be hindered.
Editor’s Note: A version of this article first appeared in the Winter 2015 print issue of Tread Magazine.