Off-road driving creates a full set of unique requirements for shock absorbers. Basically, you want the same off-road characteristics as you do in passenger car shocks; control to take good curves and a ride that is as comfortable as possible. However, in the case of off-road driving, you also want good suspension flexibility.
Raised 4x4s, which have much heavier tires, pack more heat. And if you plan to drive at high speeds, as in the case of desert racing, then your shocks are working much harder, causing much more heat.
This heat build-up leads to a couple of requirements on the shocks you need for your elevated 4X4. Both are related to adding more oil to the shock. If the oil in the shock overheats, it can foam and break. When this happens, the shock can no longer do the job it was designed to do.
The first difference with 4X4 shocks is that they have much larger bodies. The length also increases for elevated vehicles, but the diameter of the shock body also increases, depending on the space available under the vehicle, to increase the amount of oil it can hold.
The second way to increase oil volume is to add a remote oil reservoir. This option was created specifically for off-road racing and has become a popular solution for all types of 4X4.
A remote reservoir allows you to use a smaller diameter shock body, while increasing the volume of oil by keeping it in a separate reservoir that is connected to the shock by a hose or tube. The separate oil reservoir also allows for better heat dissipation.
A coilover crash is a type of crash that you will often see on modified 4X4s. This type of shock combines a shock absorber with a spring, all in one unit. They are popular in custom setups because you can combine both components while using the same amount of space.
Coilover shocks also allow the use of longer springs than a traditional coil spring suspension because the springs are fully contained. You can easily change the springs to change the spring tension, or “frequency,” as it is called.
You can also add springs for a double or triple rate spring by adding more springs with different frequencies in the coilover assembly. This will give you a smoother ride during the first few inches of compression and a more aggressive spring rate for situations where the suspension travel is beyond the normal range.
Almost all of today’s light pickup trucks come with coilover shocks straight from the factory. This has created an opportunity for traditional shock companies to offer a combination of an improved shock and a lift in one component.
Shock valves are generally designed specifically for each individual application. For example, a high-quality shock to fit a truck that has been raised six inches has valves to fit the larger tires and handling characteristics of that vehicle.
Some shocks also come with user adjustable valves. This allows you to soften the blows whenever you want, such as with rock crawling. And squeeze them for towing or general road driving.