Know Your Suspension

A Hawas
Mar 25, 2020
4 min read

Updated: May 20, 2020

Vehicle suspension has three main jobs: smooth out bumps, keep tires touching the road and control vehicle stability, let's do a quick overview;

The spring absorbs the energy of forces acting on your wheels. The two most common types of springs are coil springs and leaf springs. Both types absorb energy well, but require shock absorbers to decrease or dampen their vibration after hitting a bump.

Each vehicle wheel gets a spring and a shock absorber, but the front suspension isn't the same as the rear suspension. That's because the front two wheels must turn right and left. The front suspension also absorbs more braking torque. Accordingly, front suspensions tend to be more complex.

The front suspensions of off-road vehicles tend to be even more complicated for two reasons:

The wheels are usually bigger, and the terrain offers nastier bumps. The front suspension systems of four-wheel-drive vehicles and SUVs most often feature a solid axle with leaf springs. Such a suspension is called a dependent system because the wheels are connected laterally so that they move together as a unit.

Leaf springs attach to the frame of the vehicle and then, via U-bolts, to the axle housing. A sway bar mounted to each side of the axle controls body roll.

Other 4x4/SUV front suspensions include the following:

Solid axle with coil springs,

another dependent system that replaces multiple-leaf springs with coil springs. Many off-road drivers prefer coil springs because they have a compact design and deliver a quieter, smoother ride.

Independent front suspension (IFS),

a type of suspension in which the two front wheels move independently. an upper and a lower control arm attach to the wheel on one side, to the frame on the other side. Springing is accomplished either with torsion bars, which act like straightened-out coil springs, or coil struts, which combine a coil spring and a shock absorber into a single unit.

Twin-traction beam (TTB),

Or Twin-I Beam, combine the best of dependent and independent systems. A TTB system has two beams at the front of the vehicle. Each beam mounts on a pivot on one end, on the wheel on the other. The beams overlap quite a bit, so they act in essence like long control arms. A U-joint in the center allows for independent movement of both beams.

On the rear of most 4x4 vehicles, you'll almost always find a solid axle with leaf or coil springs. Off-road drivers often mount shock absorbers on opposing sides of the axle -- one in front and one behind the axle -- to reduce axle tramp, a rapid up-and-down motion of the rear axle caused by sudden acceleration.

Off-road Kits

Some 4x4 owners never modify the stock suspension on their vehicles, but most do. The primary goal of a suspension modification is to raise the body and frame of the vehicle to create additional ground clearance.

This also provides room for larger tires and increases suspension travel, which refers to the amount of vertical wheel movement allowed by the suspension. Several manufacturers make lift kits, or lift systems, specifically for this purpose. Before you invest in a lift kit, think about your off-road driving habits.

High-speed desert running requires a much different suspension modification than rock crawling and so on .... And don't forget to think about the on-road driving you'll have to do. If you have a dedicated off-road vehicle -- one that will be towed to and from the trail -- you might consider an extreme kit. Most people aren't that lucky, so they choose a kit that provides good performance on both street and trail. There are two basic types of lift kits. To understand the difference, it helps to visualize the foundation of an off-road vehicle. Most trucks and SUVs feature body-over-frame construction. In this design, a steel frame acts as the foundation onto which the body and all major parts are attached.

Now let's tackle suspension lift kits. These kits raise a vehicle by suspending the frame, body, engine and power train above the wheels. In other words, the distance between the axles and the chassis increases. Such a kit typically costs more and requires more installation expertise to handle any braking, steering and axle modifications that must be made to the vehicle.

Body lift kits, the second type, work a little differently. They use a system of blocks, or spacers, to raise the body above the frame. In other words, only the distance between the body and the frame increases, which means the geometry of the power train and the steering is not affected. You still enjoy more clearance for your tires without having to modify any of the core suspension components.

As a result, body lift kits cost less and require less installation expertise.

Lift kits make your vehicle more functional, but they don't necessarily make it a smooth ride. In the next article, we'll discuss the equipment you'll need for cushioning that bumpy ride and explain more about "Ride Quality"

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