Reservoir shocks help to offer even cooler operation under hard use. They’re a bit more ex
Lowdown: Shock absorbers control unwanted motion through a process called damping. They convert the kinetic energy of suspension movement into thermal (heat) energy, which is dissipated through the shock body. Without shocks your rigs springs would bounce up and down after hitting a bump (taking your rig with them) until all of the energy put into the springs by the bump was used up.
A step up from the stock shocks on your rig (which were designed for your vehicle in stock form) is an aftermarket twin-tube shock. These shocks are usually pressurized with nitrogen gas, which is mixed with hydraulic oil. These shocks are inexpensive and scores of these types of shocks are available in the aftermarket. Most use automatic velocity-sensitive valving. They’ll typically have a larger shock body, piston, and rod diameter than the factory shocks so they’ll hold up better off-road. Many companies offer twin-tube shocks valved specifically for a given vehicle, too. The downside to these shocks is that under hard use they can suffer aeration/foaming, which is the cause of shock fade.
Pros: Inexpensive, beefier components than stock
Cons: Can aerate/foam during hard use, leading to shock fade
Like twin-tube shocks, monotube shocks are typically beefier than factory shocks. Unlike twin-tube shocks the hydraulic oil and nitrogen gas are in separate chambers separated by a floating piston and this design helps to effectively dissipate heat and eliminate cavitation, which in turn reduces shock fade during hard use. They also dissipate heat better because they only have one wall in the shock body, unlike a twin-tube shock. There are a number of monotube shocks available in the aftermarket and some offer manual adjustment of the valving while others do it automatically. Monotube shocks cost more than twin-tube shocks because they cost more to manufacture. Reservoir shocks were designed primarily to prevent the aeration/foaming of the shocks hydraulic fluid during hard use. The addition of an external reservoir allows for more fluid, thus cooler operation. Reservoir shocks come in two varieties, remote (where the reservoir is mounted separately from the shock body) and piggyback (where the reservoir is mounted on the shock’s body). Reservoir shocks are great for extended hard use where the suspension is cycled quickly for long periods of time. Reservoir shocks are more expensive than monotube shocks and they take up more space than a standard monotube or twin-tube shock.
Pros: Resistant to shock fade, some are rebuildable and adjustable
Cons: Generally stiffer than twin-tube shocks (though they can be revalved to lighten damping), reservoir shocks are more expensive and require more room to mount
Another product we can thank the racing community for are bypass shocks. They have adjustable metering valves for changing the rebound and compression of the shock. In addition to being velocity-sensitive like a standard shock they’re also position-sensitive, meaning the rebound and compression can be set to be softer initially and then provide more damping as the piston travels through each different “zone.” Like a reservoir shock, bypass shocks require more mounting space. The bypass tubes can run either externally or internally. Bypass shocks are expensive.
Pros: Rebuildable, mega adjustability
Cons: Expensive, more mounting space is needed, the check valves emit a clicking noise as they open and close, complex, more maintenance
Cappa: They may look cool, but you really only need to consider bypass shocks and their complex and unlimited adjustability when you get into 14 inches or more of vertical wheel travel. They are built for high-speed and competition use. Monotube and reservoir shocks can provide more than enough damping for most 4x4s. They dissipate heat better than twin-tube shocks and in most cases the valving can be changed by disassembling the shock. However, a twin-tube shock is plenty sufficient for an everyday, daily-driven 4x4.
Holman: For my money nothing beats a well-valved monotube with a reservoir. A properly set up monotube with a reservoir will work better or as good as any shock 95-percent of the time. Sure, bypass shocks are a nice luxury if you have the space, money, and time to tune, but they just aren’t necessary for the average, and even above average, 4x4. Plus, they can be noisier and require more maintenance than a standard monotube shock.
Brubaker: There’s not a lot of high-speed desert terrain here at the Four Wheeler Midwest Bureau in northern Illinois. However, there are miles of washboard gravel roads and driving them at speed can heat up shocks and cause them to fade. I’ve heated up twin-tube shocks to the point of fade during sustained high-speed driving on these gravel roads, but so far I’ve never had a problem with monotube shocks overheating. For the money, monotube shocks are more than adequate. However, I’ll spend the extra money for a reservoir shock just to get that extra margin of cooling.