The upside to twin-tube shocks is that they are inexpensive to manufacture and they provide a comfortable, stable, all-around ride. But they are not the best choice for performance—not by a long shot.
As you would guess, mono-tube shocks employ a single tube or cylinder. Even so, they typically have double the piston power compared to a twin-tube shock. At the end of the piston rod is the piston containing the valves. On compression, this piston pushes against a section of oil that is forced toward a second dividing piston. This second, or “floating,” piston is caught between this viscose oil and a pocket of high-pressure gas between 200 and 350 psi. Since the oil is separated from the gas, the chance of foaming is eliminated. This dual-piston single-tube design is the shock of choice when corner-carving performance is desired. In addition to mono-tube shocks being able to shed heat better than their twin-tube cousins, they can also be mounted inverted when required.
So which type is the right type for your ride? If you’re just building a cruiser and on a tight budget, then a set of twin-tubes will serve you fine. But, if you want to hit the twisties and squeeze out every bit of performance from your Camaro then mono-tube is the way to go. If you’re still skeptical, then take a stroll though the pits at any NASCAR, CART, IMSA, or even Formula 1 race and you’ll find that the only cars running twin-tubes are the spectator’s cars in the parking lot.
Steve Duck, of Race Car Dynamics, spends much of his time either advising customers on what shocks will work best under their car, or diagnosing pre-existing problems. As he told us, “Oftentimes, when choosing a shock, buyers are caught up in the hype of marketing. Just because a shock is billet-aluminum and has a knob on it doesn’t mean it will work on your vehicle, or that it is even a quality shock. When I’m asked how to set up a car, the first thing I always tell people is to set it up for how it’s going to be used. If the car is going to the track once or twice a year, they don’t need a race car. What they need to concentrate on is making it enjoyable the other 363 days. There is a distinct difference between a street car and race car. A street car with the correct shocks (like the Bilsteins offered by RCD), sway bars, and springs can still be a blast at the track without killing its street manners. On the other hand, a dedicated track or autocross car must be tuned for more control by using higher spring rates and shock valving that might have less low-speed bypass to react quicker in turns. Another big issue is guys who want to have their cars as low as possible. The negative of this is they end up taking away too much suspension travel, which kills the ride and the handling. Hey, at least they still have the killer stance!”
Dialing For Dampening
Another area of choice is in adjustability. Most higher-end shock brands offer both single- and double-adjustable shocks in addition to their standard-valved shocks. In a single-adjustable shock there’s one knob that changes shock-behavior. It’s a bit unfair to refer to some of these shocks as single adjustable since clicking the knob changes both the compression and rebound at the same time, while others just change one of these parameters.
As you may have guessed, a double adjustable has two knobs: one changes the compression while the other controls the rebound. This gives the ultimate in tuning ability. Nevertheless, this is only a good thing if you set them correctly. So, if you spend the extra coin, be sure to get some tuning advice from the shock’s manufacturer or you will be complaining about your ride when the fault is yours alone.