Twin Tubes, Mono Tubes, Remote Canisters – What’s Right For You?
With all of the different types of shocks on the market and every style with a pro and con, how’s a person to choose which style to buy? The easiest way to determine which style is right for you is to do a general break down with the features and benefits of each style. But first, a little background information about the shock itself.
A shock absorber is a mechanical device designed to control vibration. It does this by converting kinetic energy (movement) into heat. Most shock absorbers achieve this by forcing fluid through restrictions to create a damping force. Restrictions include holes, discs and springs within the shock absorber to channel fluid from one chamber to another.
Modern vehicle applications use shock absorbers that consist of a cylinder filled with oil containing a piston and piston rod. Depending on the basic shock absorber construction there may be a number of restrictions to separate different chambers. In both monotube and twin tube shock absorbers the main cylinder is separated into two chambers by the piston where holes in the piston, and discs mounted to piston create the restrictions to generate the damping force.
In the majority of applications gas pressure (most commonly nitrogen) is used to prevent potential cavitation of the oil flowing through small restrictions at high speeds.
Cavitation happens when the oil becomes so hot and thin that it starts to leak through the valve and mix with the gas. This causes aeration in the oil and makes the shock ineffective. Often this phenomenon is referred to as shock fade. The result is limited damping of the suspension and very poor vehicle control. Excessive heating (as a result of overwork) should be avoided as it accelerates wear dramatically shortening the life of the shock considerably.
In mono tubes the gas is usually housed within the main cylinder and generally separated from the main chamber by a floating piston. Remote Canisters are a special type of monotube where the gas and floating piston are housed in a separate remote canister as the name suggests.
In twin tubes a second tube surrounds the main chamber to house the gas and add additional oil volume. The inner and outer tubes are separated into two chambers by a base valve restriction that contributes further to compression damping.
This style of shock is called a mono tube because the piston rod assembly runs in a single wall tube. This design has cooling advantages over typical dual tubes as the area producing the heat (piston/rod assembly) is nearly in direct contact with passing airflow, but is very susceptible to damage from rocks and other road debris. Any impact with the shock tubing will render the shock unusable.
The other potential downside to a monotube is the extended length available from a given compressed length. As the main tube in a monotube also needs to house the floating piston there is less room for rod length. Thus the rod is shorter and in turn so is the extended length.
Beyond the structural design, there are differences in the performance aspects typically associated with this type of shock when compared with others. Generally monotube shocks use higher gas pressures than dual tube shocks. This has the advantage of making the shock extremely responsive to road conditions, but can easily move towards the harsh end of the ride spectrum if not tuned perfectly to the vehicle they are fitted too. This harshness will typically be most noted at low driving speeds on rough roads.
Remote Canisters are the hottest style on the market but they are also the most expensive and require the most maintenance. So, why are these shocks selling like hotcakes? Actually, because they’re cool – in temperature, that is - and also because in some cases the shocks can be adjusted to the owners ride preference. As mentioned earlier, heat, which causes shock fade is the worst thing for a shock and a remote canister helps prevent excessive heat by putting the gas into a separate canister from the oil filled shock. This complete separation of gas and oil allows for a greater oil volume in the shock housing to dissipate additional heat and less opportunity for cavitation. The other compromise the remote canister overcomes is the compressed to extended length trade off. As the floating piston is housed in its own canister the room the floating piston would take up in a monotube can now be used up by a longer rod. The only tricky part now is trying to find somewhere to mount the canister. That’s the good news…
The bad news is that unless you are part of a skilled racing team or are a suspension engineer, you are likely not all that qualified to adjust your adjustable shocks leaving you with substandard ride quality that could adversely affect the vehicle handling and control. There is another dirty little secret about these shocks that you may not be aware of, and that is that the remote canister that holds the gas uses a Schrader valve like your bicycle tire and Schrader valves bleed off over time. So, these shocks need to be recharged and readjusted frequently – as often as every 5-10,000 miles. If you happen to have unlimited resources to compressed Nitrogen this may not be a problem, but for most people, it’s rather hard to come by. And, unreliable shops have been known to charge the canisters with compressed air instead of Nitrogen. This is very bad for a couple of reasons, first, Oxygen is not an inert gas like Nitrogen and second, air contains water and water will rust your shock from the inside out.
Bottom line, ARB only recommends their Old Man Emu brand Remote Canister Shocks for people who are racing because, generally, only people who are truly racing can induce enough heat in their shocks to benefit from this type of shock and tolerate the increased maintenance procedures involved. Basically the cost to benefit ratio simply does not makes sense for the average off roader.
OME Nitrocharger shocks are a traditional twin tube design. They use a heavy steel outer tube over the more fragile inner piston tube. This has several advantages over a mono tube design. The outer tube allows for dents and dings without altering or affecting the shock operation at all. It also creates a chamber for gas and oil to expand allowing for a greater volume of both. This gives the shock a good combination of heat capacity (what it can absorb prior to fade) and surface area to dissipate heat into passing airflow. They are a low pressure gas shock that has very soft ride characteristics at low speeds with resistance building rapidly (for vehicle control) during higher speed cycles.
Where the OME Nitrocharger differs from the average shock is in the size of the internal components used and the engineering development behind the valving. The piston shafts are constructed of 18mm diameter chromoly steel using a huge 35mm banded piston, high quality oils and other extreme duty parts for a robust, tough shock. Tuning is load and vehicle specific. Our engineers tune the shock to the particular needs of a vehicle, from stock trucks to heavily loaded expedition trucks. As a result OME often has several available part numbers for a single vehicle application allowing the consumer to choose the shock that best meets their specific needs.
OME Sport: Twin Tube With a Mono Tube Attitude.
OME Sport was developed to give our engineers more options. It’s essentially a hybrid between a traditional twin tube and mono tube shock that gives us the best of both worlds and allows our engineers to tune the shocks over a much greater range for enhanced ride and handling characteristics. The OME Sport line uses much of the same construction as the Nitrocharger shock with a twin tube body, an additional set of valves was added at the base of the piston rod to greatly enhance low speed control. The result is excellent responsive handling with good ride quality and tremendous durability in an off highway environment.