Those more educated in suspensions...

[makenzie71]

I know how hydraulic shocks work. There's oil in chamber A, seperated from chamber B using gravity. When the shock compresses, the volume of chamber A is reduced, which forces the oil into chamber B. The damping effect is created by how big the holes are between the chambers. That's it in easy terms.

Now, though, when dealing with rear shocks, you see a lot of gas charged pieces...usually nitrogen. What does this do? Why does it matter that there's nitrogen in there? Do the nitrogen and oil exist in the same chambers or are they separated? Why not just use air? Is it because nitrogen is affected less by the heat generated by suspension travel?

[jed.only]

nitrogen = inert gas.


does not vary in pressure across the temperature range as much as "air".

[jed.only]

stolen from monroe.com

One function is to increase the resistance of fluid flow into the reserve tube. This improves valving performance during the compression stroke and also prevents "dumping" into the reserve tube.
Another function is to minimize aeration of the unit's hydraulic fluid. The pressure of the nitrogen gas prevents air bubbles or foam from weakening the hydraulic effectiveness of fluid flow through both the piston and base valve systems. Foam affects performance - foam compresses, fluid does not.

[kamesama980]

basically, gas charged shocks are gonna be better. especially when pushed. regular hydraulic shocks will foam up and not work kinda like overheated brakes fade out. they tend to ride smoother to start with. the downside is you pay for the better quality.

[makenzie71]

The gas and oil are in the same chamber? What prevents the oil from settling entirely in the remote reservoirs, away from the cylinder?

[focus frenzy]

The gas and oil are in the same chamber? What prevents the oil from settling entirely in the remote reservoirs, away from the cylinder?

there is seporation, it can be a piston or a diaphram, it depends on who made it. as the shock is compressed the rod displaces some of the oil to the remote reservour, and it is forced back when the shock re-bounds. with a single tube shock a small space has to be left for the fluid to displace to.
this is also why you don't fill the forks all the way to the top. they wouldn't compress.

[Old Colt]

If the gas and oil are together, this is called an emulsion shock.
If the gas is contained in a bag as with a conventional twin tube shock this is a low pressure gas shock. This would be the Monroe and other inexpensive 15k mile shocks.
If the gas is separated by a piston in a single tube shock, this is a Dr.Decarbon style shock. This would be the KYB and Bilstein shocks.
Then we have the remote reservoir units, These will use a piston or a diaphragm to separate the oil from the charge.

The reason for the charge pressure is to reduce the formation of bubbles (Cavitation) as the oil passes through the valves.
The main reason for the use of Nitrogen is to eliminate moisture. Moisture is the component of air that has the greatest thermal expansion.