Truck Suspension Buyers Guide
Suspension is usually the first system to upgrade when you’re building an off road vehicle. Knowing that, keep in mind that the truck suspension parts you pick directly impact how much use and fun you’ll get from your rig. Make the right selections and you’ll have more fun. Make the wrong selections and you’ll have less fun. It’s really that simple.
This truck suspension buyers guide is designed to help you make the right suspension decisions. Note that these are general tips that apply to most 4x4s, and they focus on the realm of bolt-on products.
Decide where you’ll drive
First, consider where you plan on driving. Is your truck or Jeep going to split time between driving you to work and hitting the trail? A rig that’s dedicated to the trail can accommodate more extreme, in-your-face, suspension modifications. But if you still need to drive on the street, you have to consider the vehicle’s ability to brake, corner, and maneuver on asphalt. This is for your safety and for the safety of other drivers.
Pick your truck tires first
You can get good results by picking your tires first, and then choosing the appropriate truck suspension from there. Start by reviewing the suspension manufacturer’s recommended lift height for the tires. You want to keep the center of gravity low, so don’t chase more lift than what’s recommended for the tires. Also, note that a tire size recommendation from one suspension manufacturer probably won’t apply to another brand name. Pay attention also to any manufacturer recommendations regarding the offset and width of the wheels. The dimensions of your wheels do play into the lift-and-tire-size dynamic.
Premium versus economy kits
Higher lifts are more expensive, because they require more adjustments to the vehicle. Not all of those adjustments are directly related to the lift, either. You’ll face costs associated with the purchase of new truck tires, wheels, driveshafts, and other parts. Because of this, you may be tempted to purchase a lift kit that doesn’t include the parts needed to make the appropriate adjustments. This will save you money upfront, but often ends up costing you more later. You are better off selecting a lower lift, because it will be less expensive overall. Every rig has an upper lift limit, above which your costs will skyrocket. Stay below that limit and you’ll save money and trouble down the road.
Leaf spring kits
If your rig has leaf springs, installing new springs is the best way to lift it. When a leaf spring is lifted, it has a steeper arch. Also, the spring will be longer along the main leaf, to maintain the correct distance from eye to eye and the correct shackle angle. If you want more lift, you can use add-a-leafs. These can restore drooping OE springs to stock height. Expect a noticeable decrease in ride quality, though, if you use them alone.
If your vehicle has the axle mounted under the springs, you can use lift blocks to gain about 4-6” of height. Lift blocks can bring out spring wrap, because the increased distance creates a longer “torque arm.” On pickup trucks, heavier springs will usually be fine as long as the lift is 4” or less. One consideration with this method is that axle torque will strain longer U bolts. As a result, the bolts will stretch out. You’ll have to accept the responsibility of re-torquing them periodically.
Another tip is to avoid stacking blocks. Stacked blocks are prone to collapsing. Instead, consider using lifted springs and lift blocks together. Lastly, do not use lift blocks up front. A front lift block collapse would be disastrous.
You can also lift a leaf spring vehicle with longer shackles. The lift will be half the length of the increase. In other words, a shackle that’s 3” longer will deliver a lift of 1.5”. Longer shackles will alter both the pinion angle and the shackle angle. They also can reduce lateral stability and raise the load on the chassis eye. Older CJs and YJs are prone to broken shackle hangers, and longer shackles intensify this problem. You shouldn’t have any problems if the changes you make return the vehicle to the spec pinion angle and shackle angle. It’s more appropriate, though, to make limited use of longer shackles as a corrective tool.
If you have a lifted leafer, use polyurethane spring eye and shackle bushings. These hold up better than factory rubber bushings when there’s lots of flexing. This is because the center sleeve of the factory rubber bushing is bonded to the rubber insulator. This is not the case with poly. The sleeve rotates inside the bushing, which provides more flexibility. More flexibility means longer life.
Coil spring lifts
Coil spring lifts work by way of a spring spacer or a longer coil spring. A spacer lift is generally a better option for smaller lifts, to the tune of 2-3”. This is because it’s less expensive and you won’t have to make too many other adjustments to your vehicle. You keep the factory spring rates and possibly even your shock absorbers. This means your ride quality won’t change much after the lift. Coil lifts offer similar advantages, except that they cost more. If you go with new springs, you might be able to change rates to improve load capacity.
A disadvantage of coil and spacer lifts is that it changes the angles of the radius arms and track bars. On a standard four-link suspension, the lift will reduce the distance of the links from eye to eye. This changes the axle location, moving the front axle towards the rear and the rear axle towards the front. The pinion angle on both axles and the caster up front will change also. The same changes will result on a two-link, radius suspension. In this case, the pinion angle and caster changes will be more severe. It will also affect the way steering and directional stability are impacted by torque and ride height.
If you go higher than 2-3” with a coil spring lift, you’ll need what’s called a corrected lift. The most modest of these corrected kits should come with new links. The new links will be adjusted for length and they may have a different shape and/or offset bushings and drop brackets. These latter design changes are intended to fix some of the geometry issues. Track rod correction can also be used to correct any change to the angularity of transverse track bars. The bar might be longer and shaped differently. Alternatively, the angle can be corrected with a relocation bracket. This type of corrected coil spring lift can provide 4-6” inches of lift, while maintaining acceptable street performance.
The next upgrade from there is a long arm kit. The long arm setup is more expensive, but that’s not necessarily a bad thing. Long arm kits are expensive because they are engineered to deliver height without compromising performance. A long arm kit is, essentially, a new suspension system for your truck. This is one of the best options if you want an extreme lift without destroying your truck’s road manners.
Poly bushings can be handy in a coil spring lift kit, as they are in a leaf spring lift. However, in the eyes of suspension links, poly bushings can increase noise, vibration, and harshness. The hardness of a poly bushing is similar to that of rubber, but rubber does not create the same noise, vibration, and hardness problems. If you see some lift kits make use of rubber bushings, this is probably why.
Pinion and driveshaft angles
Your lift will change the driveshaft angle. If you ignore that change, you’ll experience more vibration and you’ll shorten the life of your U joint. Left unchecked, this could result in sudden failure. If the driveshaft angle is greater than 10 degrees, your U joint will start wearing faster. You don’t want to go above 15 degrees, and 30 degrees is downright dangerous.
Another result of your lift will be an increase to the distance between the transfer case output and the pinion flange or yoke. This can result in the shaft running out of slip-yoke travel. You can cure this angularity and vibration with a custom, or at least modified, driveshaft. Check with your local driveshaft shop to see what your options are. If you have no resources nearby, you may be able to mail order a driveshaft. You might also be able to find a shaft that’s already modified to suit your application; if it exists, it will be usually be offered as an add-on option with your lift kit. With a new shaft, you can also make some other upgrades, such as a larger U joint and longer travel slip-yoke. You may also want to install a slip-yoke eliminator kit or CV driveshaft.
CV driveshafts have a double-cardan joint on the transfer case end. The double-cardan joint makes use of two U joints and a special housing to halve the angularity. If your driveshaft angle is at 15 degrees, for example, the CV divides this into two joints at 7.5 degrees each.
The right shock absorber
Aftermarket shock absorbers are not universally tuned for every application. Because there are so many variables involved, picking the right shock for your lift can be guesswork. To avoid guessing wrong, go with the shocks recommended for your kit or choose an adjustable shock absorber. This way, you increase the likelihood that you’ll end up with the ride quality you want.
If you buy the recommended shocks, your ride quality will depend on the competency of the engineers. Some are more competent than others. An adjustable shock absorber, on the other hand, puts the power of tuning in your hands.
You might also be wondering if multiple shock absorbers are necessary. Sometimes they are. Maybe you have huge truck tires and one shock absorber isn’t enough. Or, perhaps you drive fast in hot conditions and your single shocks are getting fried. Keep in mind, though, that a single, remote reservoir shock absorber may be as capable as two shocks. If you get the right size shock absorber, one is usually enough.
Your lift kit will probably include swaybar link extensions or swaybar disconnects. A swaybar keeps your street driving safe, particularly if you have a coil spring lift. Swaybar disconnects, also known as tunable swaybar systems, are useful because they disengage the bit of axle that a swaybar typically limits. What’s nice with a disconnect is that you still have that bit of limitation available if you need it. If you have an aggressive coil spring lift, you might occasionally need the sway control, both on and off the pavement.
When you lift your rig or install large truck tires, you’ll probably need to make some steering improvements. Certain upgrades, like dropped pitman arms, should be included in your kit. If your steering is not as responsive as it should be, an aftermarket steering damper designed for oversized wheels and truck tires should help. Also, big wheels and tires put a lot of strain on your steering system, and so the following upgrades may be needed:
- Stronger tie rods and drag links; larger tires can twist up your stock tie rod
- An upgraded steering box and pump and, possibly, a hydraulic assist; these are needed if your power steering starts running out of power
- A power steering cooler; the larger truck tires can heat up your power steering oil
- Bracing and frame reinforcement for steering box mountings
Conventional wisdom says if you increase your tire size in excess of 15% and you use the rig for off-roading, you should upgrade your steering.
Not all truck suspensions are equal, but the old advice “you get what you pay for” is usually accurate. Check with a 4 Wheel Parts technician for any specific questions regarding the requirements for your application.