Twin Tube Shocks Twin-tube shocks, are, for the most part, the definition of a standard shock. Nearly all of the text above defines how this shock works, so we won�t get into much more detail. What we will say is that a twin-tube shock is the “entry level” shock absorber if you were to compare all shock absorbers against each other. These are considerably cheaper to manufacture, but offer the least consistent dampening in comparison. Twin-tube shocks are much more susceptible to fade, aeration and heat dissipation.
Coil-Over Shocks Coil-over shocks are fairly simple by design. Simply put, a coil spring is placed over and around the shock body, adding an additional spring rate to the shock absorber. These coils can be placed over just about any type of shock absorber depending upon the manufacturer. Unless you have a specific need for these shocks, or if you plan on using this design in lieu of leaf or coil spring suspension altogether, don�t bother.
Gas/Pressurized Shocks First, let�s dispel an old wives tale that gas shocks are much more stiff than regular shocks, offering a harsher ride. Gas shocks can be valved differently to offer a ride just as smooth as a twin tube shock, while still providing far superior shock-damping consistency than any regular shock on the market. Now, with that said, let�s define what a gas shock is and how it works. Let�s say your driving your rig at a good clip down a washboard road. Your suspension will be cycling at a tremendous rate, thereby forcing the piston within the shock absorber to move at a tremendous rate as well. When this happens, the oil within a regular shock absorber gets air bubbles forced into it, forming a frothy, foamy goo. When this happens, the oil will flow through the orifices of the piston at unpredictable rates and decrease the performance of any standard shock.
Gas pressurized shock absorber works a bit differently and are not nearly as vulnerable to the oil aeration as a standard shock absorber. Reason; gas pressurized shock absorbers are built with pressurized nitrogen inside the shock body. The pressure can range anywhere from 80 to 350 or more p.s.i. This keeps the oil from aerating because nitrogen does not mix with the shock oil, and forces the oil molecules to stay packed together much more closely, thereby all but preventing the oil from getting any air bubbles within.
Mono-Tube (Single Wall) Shocks
These shock absorbers types use a single-wall shock tube to enclose the piston, the shock oil and (sometimes) the pressurized gas. These shock absorber types are much more precise at dampening than the standard shock absorber because they are made with considerably more precise standards during the manufacturing process. Additionally, in most cases, the single-wall shock absorber is considerably stronger than the twin-tube shock absorber because they typically use a larger diameter piston. Further, the single-wall absorber is more resilient to shock fade because it can divide the shock�s oil from the air space far better than a twin-tube shock. With this type of construction comes the benefit of better heat dissipation as well.
Shocks with Reservoirs
Contrary to popular belief, the external reservoir on a shock of this type isn�t made to hold extra shock oil. Its purpose is to house the extra needed air space during a shocks compression cycle. Typically this is not air at all, but nitrogen. It will hold some additional fluid as needed, but this shock is designed differently from most other shocks in that the entire main shock body is completely drowned in shock oil. All shock absorbers, regardless of the type, need some amount of dead air space to allow them to work properly. Standard shocks have dead air at the top of the valve body or utilize a twin-tube model for the needed expansion.
As mentioned previously, the external reservoir is used for storing the extra needed dead air space. They are typically connected to the main shock body via a reinforced flexible hose or a metal tube of sorts. The trick here is that as the shock compresses, the extra oil is forced through the connecting tube, into the reservoir body and forced against the pressurized air or nitrogen. In theory, if the oil and the air are not allowed to mix (that�s the way the engineers designed this), the shock will dampen at a far more consistent rate regardless of the frequency of the shock compression/rebound cycles, because the oil cannot aerate. Not to mention they look cool.
Bypass Shocks
The dampening provided by standard shock absorbers is provided by the valving system being located at the head of the shock piston, which determines the dampening rates. Bypass shock absorbers aren�t all that different in that aspect, but they do add to this standard method of dampening via valving. How? Bypass shock absorbers add the component of external metering valves that are completely adjustable with spanner wrench for changing the rebound and compression of the shock. The other major aspect of bypass shocks is their oil-looping design. As the piston is compressed into the body of the absorber, the oil is pushed through the external bypass tubes and looped back underneath the head of the piston. Transversely, under rebound, the fluid does the same thing, only in reverse. This entire process is metered and dictated at an adjustable rate defined by the external, adjustable check valves. Depending upon make and model, some bypass shocks can offer multiple tubes to the shock body, typically one for rebound and one for compression. Some of which have multiple, adjustable check valves to control the metering of compression and the metering of rebound.
Adding fuel to the fire, yet another reason why bypass shocks are the best of all dampeners is because they�re not only velocity-sensitive like all other shock absorbers, but they are also position-sensitive as well. What does this mean? Simply put, these shocks can use a variable metering system that allows the shock to offer a much softer rebound and/or compression rate initially, and increase the dampening effect as the compression or rebound increases, similar to progressive coil springs. The really cool part? If you have the cash, all of these aspects of a bypass shock can be built to your needs and adjusted based upon the type of wheeling you do!
Dual Shocks?
One piece of advice� don�t run dual shocks just because they look cool, OK? However, if you get frequent heat-induced shock fade and don�t have the budget for reservoir or bypass shock absorbers, you may benefit from running a dual or triple shock setup. However, this doesn�t mean that you just slap another set (or two) of shocks in addition to your existing ones. You should get a set of more lightly valved shock absorbers to replace the ones you have now. Do the homework and figure out how much absorbing your shocks need to do before you add some more, that is unless you don�t like the fillings in your teeth.
Upside down?
Unless your shocks are specifically designed to be mounted upside down or designed to be mounted in either direction, please follow the rule stated above for dual shocks. As a rule, dual tube shocks should never be mounted upside down. Some people say that monotube or gas pressurize shocks can be mounted upside down, however in time they will develop and extra inch or more of piston travel that has little to no dampening effect whatsoever. Ultimately: don�t mount shocks upside down just because it looks cool. Sometimes a shock must be mounted upside down due to space limitations, or to protect the shock body, if this is the case, make sure you use a shock designed to be mounted upside down.
How can I tell if I need to replace my shocks?
While a leaking shock is an obvious sign of a shock-gone-bad, many shocks wear out without losing any oil. One of the best ways to determine if a shock needs replacement is to perform the jounce test. Simply bounce the front or rear end of your rig by jumping or pushing up and down on it for a few seconds, then let off. If your rig continues to pogo for more than 1 to 1.5 bounces, you may need to replace your shocks.
To boot or not-to-boot
A while back this use to be yet another one of those campfire arguments� do I run shock boots or don�t I? While some manufacturers recommend that you do, some do not. The general consensus throughout the 4-wheel drive world now is that you should run shocks without a boot. Reason; when 4-wheeling, the amount of dust, dirt, grime, mud and grit generated is far more than that of a normal car, driving on the road. With a shock boot in place, the nastiness will get caught inside the boot and can�t be removed. The grit and grime will load up on the piston rod because of the thin oil coating. This grit will ultimately score not only the seals of the shock, but the shock piston rod as well, causing oil seepage and ultimately, the demise of the shock itself. Running without a boot will allow you to blast that crud away with a garden hose and a soft cloth.
What kind of shock do I need?
Only you can answer the question of the type of shock you need, and this is based upon your budget and the type of wheeling you do. You should also talk to some people who have a similar vehicle as your and do the same types of off-roading. However, here are some very basic guidelines.