The basic theory behind shocks is that they absorb and dissipate the energy and shock between the road or trail and the vehicle. The cylindrical contraptions have a telescoping rod on one end that's fitted with valves; the other end is immovable and affixed to the frame or axle of the vehicle. There are two basic mechanical movements of a shock absorber. When a vehicle drives over a bump, the shock compresses, pushing the piston into the shock. This is called compression. When the vehicle clears the bump, the shock decompresses. This is called rebound. Shock cylinders are filled with either hydraulic fluid, gas, or air. As the vehicle travels down the road, the wheel moves up and down with the contour of the road. This creates energy, which is absorbed by the action of the valve as it passes through the oil or gas in the damper.
Shock absorber theory may seem basic, but the mechanics, physics, and science that go into them can be mind-boggling. The dampers smooth the ride by working in conjunction with the springs. It's important when building a vehicle that the two components be properly matched and complement each other. If you have just spent money on a set of custom leaf springs, then don't buy the cheapest hydraulic 50/50-valved shock you can find. Some of the low-end shocks aren't valved vehicle-specific. This means a company that sells a shock for a fullsize Ford truck is selling a shock for a midsize Toyota truck with the same valving. What does this mean for you? Poor or limited on- and off-highway performance.
When it comes to choosing high-quality shock absorbers, the selections are nearly limitless. The key to choosing the right shock is doing your research and knowing exactly how it will perform on the highway and out on the trail. Your choices are hydraulic shocks, mono- or multitube shocks, coilovers, bypass shocks, and gas and air shocks.
One key factor in the selection...
One key factor in the selection of shocks is measuring for the right compression and travel length. If the shock is too short, the travel and compression of the vehicle's suspension and axles will be limited. Don't just buy shocks because they are a great deal--purchase them because they are the proper fit and offer the performance you are looking for. The wrong-sized shock will likely suffer an early demise in harsh trail conditions. If your suspension ends up with more travel than the shock allows, consider installing a limiting strap.
Standard shocks are velocity-sensitive--the...
Standard shocks are velocity-sensitive--the faster they move, the more damping force the shock applies. This allows the shocks to adjust to on- and off-road conditions, and these shocks work well in high-speed applications. But with speed comes high temperatures, which lead to shock fade. If speed is your thing, you might want to consider a larger-diameter shock or a shock with a remote reservoir that holds more oil. These shocks will help alleviate fading caused by overheating.
Some of the most complex shocks...
Some of the most complex shocks available are multibypass shocks. Sensitivity of rebound and compression are set in stages; this is based upon where the bypass tubes are placed on the body of the shock and where the valve is in its compression's stroke. A long rebound may be stiff at a certain point in compression.
The advantages of adjustable...
The advantages of adjustable shocks are well worth the additional money. Rebound and compression throughout various stages of the shock's compression are easily controlled with the turn of a dial or knob. These are good all-around shocks. Ride comfort can be adjusted for tough trail conditions or a highway-friendly ride. Some companies offer systems that let you adjust the shock's rebound and compression from inside the vehicle.
Air shocks have become extremely...
Air shocks have become extremely common for hard-core trail rigs and rock buggies because the compression and rebound are easily adjustable. The air acts as a spring, which can be adjusted by the volume of air in the shock. Air shocks are usually built for the most extreme rockcrawling conditions with hardened chromoly tubing and shafts of 1.25 inches or more in diameter. These may not be the most high-tech shocks, but they serve a purpose.
Coilover shocks are complex...
Coilover shocks are complex components, but tried-and-true and a common sight on a well-built trail rig. Manufacturers have gotten the damping characteristics of these high-tech shocks down to a science. Coilovers can be ordered with close-to-optimal ride qualities for the conditions you want to wheel in. Setting a custom 4x4 up with coilovers may be more difficult when it comes to figuring out the proper spring rate and valving. The factors can be determined by trial and error or by a slightly more scientific approach.
Shocks filled with nitrogen...
Shocks filled with nitrogen or another gas help alleviate vacuum and cavitation through thermal expansion. A twin-tube gas-charged damper has a low-pressure charge of nitrogen gas in the reserve tube. The nitrogen gas helps to improve the ride control of the shock. The gas minimizes the aeration of the hydraulic fluid by compressing the air bubbles and keeping the fluid from foaming. Hydraulic fluid that's foaming can be compressed--fluid that's not aerated does not compress.
A monotube shock is just what...
A monotube shock is just what it sounds like: The piston rides in a single cylinder. The benefits are that these shocks are more economical, and they dissipate heat better than a multitube shock. The drawback is that if the tube is dented or damaged the shock will more than likely be ruined. Multitube shocks offer less heat dissipation but better protection in off-road conditions. If the outer tube is damaged, the inner tube stands a better chance at staying true.
Most shock manufacturers carry...
Most shock manufacturers carry two lines of shocks: a premium shock usually associated with racing, and an enthusiast series. Racing shocks offer better quality with heat-treated metals and better valve material. The enthusiast level is still a good-quality shock but isn't constructed with the best and most expensive materials.