Off Road Shock Absorbers 101

Let's face the facts: When it comes to suspension components, some are easier to understand than others. Springs control height and load. You can see all of the parts, and they are fairly easy to figure out. But shocks-that's a totally different story. All of their work takes place inside a tube. You can't see the hardest-working parts of the shock, and how they work is a mystery to most people.

To shed some light on what magic goes on inside the tubes under your 4x4, why some shocks cost $20 and others cost $200 and, most importantly, what you need to know to figure out what's right for you, we talked to Bill Johnson at Rancho and Shane Casad at Bilstein. These companies are two of the original manufacturers in the shock industry. The innovations from these companies span more than 150 years combined, and their involvement in four-wheeling gives them considerable knowledge and insight into the technology of shock absorbers.

A shock is a shock is a shock, right? The shock absorber is the controller in your suspension system, therefore playing a key role. There are several different designs used for 4x4s, and an unlimited number of tuning possibilities within each design. Choosing high-quality aftermarket shocks can be one of the best improvements you make in the ride quality, performance off-road, and handling on-road of your vehicle.

A shock is a shock is a shock, right? The shock absorber is the controller in your suspens

What Shocks Do
Simply stated, shock absorbers control the up-and-down motion in a suspension system. Technically speaking, shocks convert kinetic energy into thermal energy. Shock absorber are also referred to as "dampers" because they dampen the energy of the spring. By creating resistance to up and down motion, the dampers turn motion energy into heat, and then dissipate the heat to the atmosphere.

Without shocks as part of your suspension system, two things would happen. First, when a tire strikes an obstacle, the springs alone would react to the impact, sending the vehicle's suspension into an undesirable undulation. The result would be a loss of control as the body and axles moved out of synch with each other. The second result would be that the suspension would move up and down until friction returns the vehicle to static ride height.

That's the Shock 101 lesson. To understand more, let's talk about the components inside a damper.

Off Road Shock Absorbers 101 Bilstein Internals

The most affordable shocks are a standard hydraulic design. These work okay in mild applications, but are susceptible to cavitation, or the mixing of oil and air. This occurs in hydraulic fluid when the shock is worked hard, and over time the shock loses its ability to perform. A monotube shock (such as the Bilstein shown) uses pressurized gas, usually nitrogen, under a floating dividing piston (A). Because of the pressurization, the oil in the shock cannot foam. The other mechanical parts inside a monotube shock are the piston and valve assembly (B) mounted on the end of the rod inside the shock body. The valves in this assembly control the resistance to up-and-down movement. Changing the valving in this assembly is the primary way a shock is tuned for a specific application.

The most affordable shocks are a standard hydraulic design. These work okay in mild applic

How They Work
The parts of a shock that you can see are the body and the rod. Inside the shock body is a piston assembly that includes a valve system. This piston and valve assembly is most often attached to the rod, but can also be mounted to the shock body. This valving is one of the things that shock companies use to tune a damper for a specific application. The valve stack creates resistance to the rod moving up and down, controlling the motion of the suspension. This resistance is how the damper converts energy into heat. So, a secondary function of a shock is to dissipate that heat. The heat is transferred from the fluid in the shock to the shock body, and then to the air.

There are variations to this, but for now, we want to keep things simple, and this understanding applies to just about every type of shock in the 4x4 market.

The Right Shocks for Wheeling
Off-road driving creates a unique set of requirements for a shock absorber. Generally, we want the on-road driving characteristics of a passenger-car damper: Control for good cornering and a comfortable ride. But we want longer travel for good suspension flex. Lifted 4x4s, with much heavier tires, build more heat. And if you drive at high speeds, such as those of desert racers, then you really work a shock, generating a lot more heat.

This has led to a couple of changes in shocks for lifted 4x4s. Both are related to adding more oil in the shock. If the oil overheats, it can foam and otherwise break down. And at that point, the shock loses its ability to do its job.

Every shock manufacturer has its own philosophy of shock valving. Specific shock valving is different within the same shock model for a 3/4-ton truck than it is for a Suzuki Samurai to cope with vehicle weight and typical use. In almost all cases, this valving is locked in by the manufacturer. The Rancho RS9000XL, ProComp's MX series, and Walker Evans 500 series shocks are unique in that each gives you an adjustable range of valving, so you can effectively soften the valving for rockcrawling and firm it up for freeway driving or towing.
Every shock manufacturer has its own philosophy of shock valving. Specific shock valving i
One thing you need to know when considering shocks for your lifted 4x4 is how to find shocks that fit. Every suspension lift provides a little different suspension travel, requiring a slightly different shock. If you simply purchase a shock for the amount of suspension lift you have, you'll get a shock that will work, but it may not be optimal. Having the wrong length shock can damage the shock or limit suspension travel, neither of which is desirable. Every modified 4x4 is unique, and the best way to find what shock length you need is to actually measure yours.
One thing you need to know when considering shocks for your lifted 4x4 is how to find shoc
There are four common mounts that you'll find for 4x4 shocks. The most common for lower mounts is a U-bracket that slides around both sides of the lower bushing. The shock has a round eye with a bushing and metal insert sleeve (A). Another mount is a stud type. The shock looks the same except the metal insert sleeve isn't used. This is a common top mount for front shocks. The third type is called a stem-top and utilizes the threaded top section of the piston rod (B). The rod, with an series of bushings, stops, and washers, attaches to a bracket on the frame rail. This top mount can be found on the front of several types of vehicles. The fourth type has a barpin inserted through the center of a shock bushing (C). This barpin bolts to the chassis. This is a common upper mounting method for rear shock arrangements.
There are four common mounts that you'll find for 4x4 shocks. The most common for lower mo

To properly measure shock length, you will need to completely flex your suspension. Ideally, you'll want to fully droop your front left corner, and completely compress the rear right corner. An RTI ramp is helpful, but some decent terrain will work just as well. When the vehicle is stable and it is safe to reach under the vehicle, measure the maximum and minimum length of the shocks. Then reverse the flex to check the other side. Note if any shocks are maxed out in either compression or rebound (droop). If so, remove the shock and measure from mount to mount. Then use the charts most manufacturers have online to determine which shocks will really fit your 4x4.
To properly measure shock length, you will need to completely flex your suspension. Ideall
A word of caution regarding shock length: a shock should not be what limits suspension compression. This is the job of the bumpstop,and shock damage may occur if the shock bottoms out before the bumpstop limits compression. This is not imperative on droop, as most shocks have a built-in stop. However, in extreme off-road conditions such as prerunning or racing, a limiting strap should be used to avoid possible damage to the shocks, brake lines and other components.
A word of caution regarding shock length: a shock should not be what limits suspension com
Heat management is a secondary job of a shock. One way of improving the heat management is to add more oil. Larger-diameter shock bodies do this in some applications, and the remote-reservoir shock was invented to add significant oil capacity. The Bilstein 9300 Black Hawk uses a remote reservoir, and the shock body is made from 6061 extruded aluminum with a hard-anodized finish, which the company has found can reduce the operating temperature by up to 100 degrees in racing conditions. The shock also features incremental flow metering valve with nine settings for you to fine tune the valving.
Heat management is a secondary job of a shock. One way of improving the heat management is