Probably The Most Overlooked And Most Important Part Of Your Suspension
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.
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.
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.