Twin-Tube Vs. Mono-Tube Shock Absorbers

An in-depth look at the differences between twin-tube and mono-tube shock absorbers.

Hello there, I’m Mac and this is Aaron. We’re going to show you the difference between a twin-tube and a mono-tube design shock absorber. To do that we’re going to use the specially made clear demonstration units. This one is an example of a typical twin-tube unit, and this one is a mono-tube shock absorber. As you can see, both the twin-tube and mono-tube designs use hydraulic fluid and mount on the vehicle the same way.

Let’s begin by looking inside the twin-tube. It uses two separated fluid areas, an inner working cylinder, and an outer fluid reservoir that acts as an expansion area. In a gas shock, all of the oxygen air is replaced with a low pressure nitrogen gas, about 50 to 100 pounds, to reduce foaming. The basic components are a shaft and piston that move up and down inside a working cylinder. There are hydraulic valves inside the traveling piston, and there’s also a hydraulic base valve at the bottom of the working cylinder.

The fluid is pushed back and forth between the inner working cylinder and the outer fluid reservoir. As the shaft and piston passes up and down, you can see that fluid passes in and out of each cylinder. The calibrated resistance that each valve provides to fluid travel is what determines the amount of damping force that the unit will have. This basic function works well for most vehicles, especially when a vehicle is used in normal to moderate situations, and when passenger comfort is most important. However, during more demanding conditions, when the shaft and piston are moving more rapidly or traveling further, a churning effect and foaming starts to occur.

This condition decreases its effectiveness. In fact, performance in some cases can be reduced as much as 50%. This condition is similar to having air in a break fluid line, which causes a spongy brake pedal. The KYB twin-tube shocks and struts use high quality valves that improve fluid flow and create less churning. They also utilize and anti-foaming check valve at the top of the expansion area to reduce the amount of gas entering the fluid chamber and thus maintains a higher level of performance.

Now, let’s compare the twin-tube design to the mono-tube. The purpose for the mono-tube design is to have a shock absorber that is more responsive, has additional body control, will not have any fluid aeration, and still has a comfortable ride. As you can see, the mono-tube has a single cylinder, a wider piston, and doesn’t use an outer fluid reservoir. The entire diameter becomes the working cylinder, which increases the hydraulic valving area.

The mono-tube uses a high pressure nitrogen gas, typically 250 to 300 pounds. The gas pressure and the hydraulic fluid are separated by a floating piston so that the gas and fluid never mix. The gas areas becomes the expansion chamber, and the fluid portion has 100% fluid. Because the two never mix, it eliminates foaming, and the hydraulic valving becomes much more responsive.

During vehicle movement, not all of the movement can pass through the valving. This puts pressure against the floating piston and the nitrogen gas chamber. On lighter movements, it has a cushioning effect. But on more aggressive vehicle movements, the gas pressure increases quickly and offers additional resistance. This gives the mono-tube variable performance based on driving conditions. Higher performance, just when needed.

You can also see that no matter how aggressively Aaron pushes and pulls, there’s never going to be any aeration. The mono-tube fluid holding valving guarantees that, so the vehicle will never have any performance fade conditions. That’s the mono-tube. It provides a more responsive vehicle control, additional vehicle stability, and less body roll. Did you know that in some vehicles they come factory equipped with a mono-tube? The KYB gas adjust is the right replacement mono-tube for those vehicles, but since most vehicles come equipped with a twin-tube design, the gas adjust and the mono-max, which are both a mono-tube design, become a performance upgrade.

KYB offers mono-tubes for many passenger cars, vans, SUVs, pickups, and light trucks. It’s a great choice when you want quicker response and increase your vehicle’s handling and control. Thanks for the help, Aaron. I hope this helps explain the differences between twin-tube and mono-tube. KYB gives you the choice to restore your vehicle’s originally designed performance, or to add more with mono-tube.