Shock Guidance - Jeep Damper Selection BasicsPosted in How To: Suspension Brakes on September 4, 2013
How can something as simple as figuring out which shocks are right for your Jeep be so perplexing? The problem is that they all look basically the same from the outside, and the most important technical data that would help you choose wisely is proprietary, with the shock manufacturers keeping it close to the vest.
While our attempts to pry the technical data from certain shock engineers with interrogation and bribes failed, we did uncover enough dirt to offer you assistance in upgrading the shocks for your ride.
The first level of separation is between twin-tube and monotube design. Put simply, twin tube shock design is the older technology. It has been used in generic passenger cars as the stock shock technology and is good enough for low-performance vehicles with stock tires. The hydraulic oil and gas (usually nitrogen) are mixed together it the same chamber. These are often called hydraulic shocks. There is an inner tube in the shock construction where the rod pushes up and down against the oil and gas mixture. There is also an outer tube that acts as a reservoir. Their shortcomings are that they overheat more easily and are prone to aeration, which causes them to fade. As you work your suspension harder with heavier wheels, tires and axles, you’ll exceed the limits of this technology.
Monotube shocks have been around for quite some time, and they are generally considered the higher performance technology. These are often called gas-pressure shocks. The primary difference is that the hydraulic oil and nitrogen gas are in separate chambers within the same tube, and are separated by a piston that floats up and down inside the tube. They run cooler, don’t have aeration issues and generally can handle a lot more punishment.
Monotube shocks can be mounted with the reservoir on the top or bottom, while manufacturers tell will tell you that twin-tube shocks must be mounted with reservoir on the bottom.
Monotube shocks dissipate heat better and are less prone to aeration.
There are a few terms you need to be familiar with to understand what it is you’re looking for in a better shock. Compression is the ability of the shock to control or resist being compressed. This has the biggest impact in ride quality on- and off-road. It is also what helps keep tires planted on the pavement as you go around corners, not that it is usually a priority for our off-road Jeeps. Rebound is how the shock extends. When you drive over a pothole, a shock with soft rebound will let the wheel and tire drop quickly, while stiff rebound drops more slowly. The last term is valving. You’ll hear people talk a lot about stiffer or softer valving in a shock. This is primarily describing the mechanism that lets the oil in the shock go past the piston. Typically, shims of various thicknesses are attached to the piston to make it easier or harder for the fluid to move around the piston, affecting both rebound and compression. Almost every shock has a 60/40 split in the percentage of flow, with 60-percent compression resistance and 40-percent rebound resistance.
A variation of the monotube design is the remote-reservoir shock. These have a separate canister that holds additional gas, enlarging the body of the shock. Sometimes the piston stack is moved from the tube to the remote reservoir, which improves uptravel for a given shock shaft length.
These originated in off-road racing where standard shocks would overheat, even when running multiple shocks at each corner of the vehicle. An additional benefit is the ability to better control the gas-pressurized function of the shock through a larger volume.
Another variant includes adjustable shocks. The original adjustable shock in the off-road market is the Rancho RS9000 (well, actually it was the short-lived RS7000), with the latest version called the RS9000XL. These shocks have tri-tube construction: a pressure tube where the rod and piston move, a secondary tube and a reserve tube. A knob at the base lets you dial in your preferred ride quality, adjusting both compression and rebound by restricting fluid flow from the secondary tube to the reserve tube. Fox also offers an adjustable shock, with a knob on the remote reservoir. These adjust compression only.
This brief overview of shock technology should help you sort through the options available for your Jeep.
When To Change Springs Too
Sometimes you may be thinking about changing shocks when you should really be thinking about your springs. A lift kit will often include springs that have a higher spring rate than factory. The reason for is that a higher spring rate will help lift a vehicle in addition to a taller coil spring (or a leaf spring with more arch). We also often add a lot of weight to our Jeeps with a winch, heavy bumpers, V-8 engines and so on. The purpose of the spring, however is to hold the vehicle up. Adding spring rate when you aren’t adding weight will result in a stiffer ride.
That’s one reason that Off Road Evolution introduced its Plush Ride coil springs for JKs. These provide the 3-4 inches of additional height that is desired without a significant increase in spring rate. If you’re looking for a better ride, shocks may be part of the solution, but consider whether you’re fighting a spring with more spring rate than you really need.