If you’ve been shopping for off-road shocks for longer than ten minutes, you’ve likely run across a set or two that are equipped with external reservoirs. While they undoubtedly look cooler, you may be curious as to why it may or may not be necessary to fork over a premium for the upgrade.

What, Exactly, Is Going On In There?

Before we can understand the reservoir’s reason for being, we need to wrap our heads around actions inside of the shock. In most modern applications, the shock absorber consists of a metal tube with a sliding rod sticking out of one end. On the end of the rod that lives inside the shock tube, there is a valve that is precisely the diameter of the inside of the tube.

Also inside the shock tube is a hydraulic fluid, even if the shock is gas-charged. As the suspension compresses and relaxes, the shock rod (and valve) move up and down on the shock’s tube. That fluid puts friction on the valve as it moves, thus creating a dampening effect. Without the shock, the spring would jounce and rebound several times after it hits a bump and the vehicle’s handling would be terrifyingly unpredictable.

Cool. So What’s the Reservoir For?

Heat becomes a by-product of the friction created from passing the shock’s valve through its hydraulic fluid. The reservoir allows for a greater volume of hydraulic fluid to be present. Simply put, the more fluid there is, the more heat can be dispersed.

Generally speaking, a standard shock holds more than enough hydraulic fluid to handle the heat dissipation of day-to-day driving. In extreme off-road environments, where the suspension experiences frequent and violent hits, a standard shock runs the risk of overheating. When this happens, the hydraulic fluid begins to foam and loses its ability to apply friction on the shock’s valve. The end result is terrifyingly unpredictable handling that’s similar to not having a shock at all.

The bottom line is that an external reservoir allows the shock to more effectively disperse the extra heat generated from extreme operation. Additionally, most reservoir shocks offer an increased travel over their standard counterparts and some even offer the ability to customize the valve settings.

Okay, I’m Sold. Now Where Do I Put the Reservoir?

The shock’s reservoir can be mounted almost anywhere, limited only by the length of the hose that attaches it to the shock and proximity to moving suspension components. If such a mounting location is unavailable, there are several solutions for mounting the reservoir directly to the shock, including Supreme Suspensions’ own Shock Reservoir Clamps.