writer: Sean P. Holman, Courtesy Of Bilstein, Kore Performance
With the price of admission into newer vehicles steadily climbing, 4x4s are being asked to be more and more versatile, doing everything from handling your daily commuter chores to primary trail rig duty. So what do we consider the most important element of your vehicle if you want to experience a serene ride over glass-smooth blacktop, controlled bounding over a fast sandy wash, or steady clambering up a boulder-strewn route? The answer is easy: your shocks. While shocks are fairly simple in principle and design, we'll walk you through the basics and answer some common questions to better help you understand what makes shocks an important aspect of your trail rig, and hopefully arm you with enough knowledge to take the edge off of your next shock-buying experience.
What Are Shocks?
If we are going to discuss the basics of how shocks work, then we will start by defining what a shock is. A shock is simply a hydraulic device that converts kinetic energy (movement) into heat energy, which is dissipated through the shock body.
What Do Shocks Do?
Basically, a shock controls the up and down movement of a vehicle. Now you might say, "Hey, what about springs?" Well, a spring supports the vehicle's weight and only allows up and down movement of the suspension, but doesn't control it. Without shocks on your four-by, you will bounce and bob down the highway, and crash and bang on the bumpstops over each and every surface imperfection. A shock's primary function is to dampen the spring movement and keep your tire in contact with ground at all times, providing the driver with comfort and control, through handling and braking. In fact, worn shocks actually contribute to longer braking distances, something our heavy rigs with giant meats tend to be sensitive to. Spring rates only control the movement of your chassis, but shocks control the length of time it takes for each of these movements to occur.
Think of shocks as timing devices. Without shocks, consistent tire contact patches would not exist, and controlling the vehicle would be nearly impossible.
How Do Shocks Work?
To understand how a shock works, we must understand the different parts that make up a shock. The first thing you notice when looking at a shock is the shock body. This is what mounts to the vehicle and houses the air and hydraulic shock fluid. The next thing you'll see is a chrome rod, sticking out of the body. This is the shaft, which also mounts to the vehicle, and moves up and down with the suspension movement, also called a stroke. Inside the shock body, a piston sits on the shaft, and has a series of shims connected to it with various-sized holes that allow the shock oil to pass through them as the shock compresses and extends. Unlike air, hydraulic fluid cannot be compressed, so as the piston travels up and down within the shock body, fluid is forced through the shims, resisting vehicle movement. With more or bigger holes, there is less resistance, and the shock piston travels through the oil faster, creating a softer shock action. The opposite is true with less, or smaller holes.
Premium shocks have the added benefit over standard shocks because they replace the air with a pressurized gas, such as nitrogen. Nitrogen resists cavitation, or the forming of air bubbles in the hydraulic fluid. You have probably encountered cavitation if you have ever taken a stock vehicle down a fast sandy wash and experienced the vehicle becoming uncontrollable after a fairly short distance, only to find the symptoms disappearing after a short time of the vehicle sitting and the shock oil settling and cooling down. A shock which has cavitated can no longer provide the resistance necessary for the shock to do its job.
How Do I Know If My Shocks Are Bad?
Shocks usually wear out gradually, but some things can happen, especially off-pavement, to hasten their wear. One of the first things to look for is either a nicked or bent shaft, which can easily be caused by flying gravel or debris. Once damaged, the shaft can allow contaminants to enter the oil and destroy the piston seal, which will eventually lead to a leak of the shock fluid.
If not replaced, the shock will eventually lose its ability to function properly. Other signs of worn shocks are excessive bouncing after crossing a dip or bump, rocking back and forth after a stop, excessive body roll around corners, tire cupping, and straight-line braking that isn't so straight.