Nitrogen in Shocks

[fabr]

Nitrogen in your air bags wouldn't gain any performance, nitrogen is usually used in racing because it is a known element over outside air that can have more or less humidity and is a lot more stable.

Nitrogen ,which is a larger molecule will not nearly as easily leak out .I have a set of large drag slicks that have been sitting with the dragsters weight on them ever since I hung up drag racing. In 20+ years I have only added a small amount of Nitrogen one time. I need to do it again now,probably 3 psi. Nitrogen will also add life to the rubber components since it does not oxidize rubbers.

 

[madweazl]

All of the nitrogen is on top of the piston in the reservoir and just keeps the fluid under pressure. As the shock compresses the shaft displaces fluid and it goes into the wet bottom side of the reservoir. Changing the nitrogen pressure does change the stiffness of the shock in general but not because of the valving but rather because of the more or less resistance of fluid trying to move into the reservoir. Using the valving and/or bypass tubes is how the shock was engineered to dampen shaft movement not the pressure above the floating piston. If you want more dampening give the bypass adjusters another half or full turn at a time and retest, and which ones to adjust depends on if you want more compression or rebound dampening, bypass tubes are typically set up with the longest compression tube being near closed to act as a bump stop when it's near the end of it's travel. A good way to determine if your car needs adjustment is to film it driving over whoops and then go back and look at the video, you can get a good idea where an improvement can be made if you find the back wheels buck over the tops of whoops, you need more rebound dampening to slow the suspension movement down. Just the opposite on the compression if it rides harshly. I'm far from a suspension guy but I've played with mine enough to know what the tubes do.

And I do not like the idea of removing valving from the coil over shock, it places all of the dampening responsibility on the bypass and overheats the fluid unnecessarily.

There are many variables here other than just rebound control. Too much compression damping could cause "pack" which just bounces off the whoop or too little damping could let the shock bottom causing it to buck. Wont disagree that a video is helpful to diagnose what is happening. The longer tubes are likely used to bypass the shim stack when the shaft is near full extension, controlling how it performs over the smaller bumps.

 

[KLC]

What's the complaint you're trying to address?




The longest tube is usually in the ride height zone, which most prefer to keep open as much as possible to allow the suspension to move on chop/chatter bumps. The short tube is usually just before the bump zone, and closing this tube will help the most on easing the transition to the bump zone and prevent bottoming with less impact on your back.

View attachment 134531

I should have stated I use Fox.

 

[KLC]

There are many variables here other than just rebound control. Too much compression damping could cause "pack" which just bounces off the whoop or too little damping could let the shock bottom causing it to buck. Wont disagree that a video is helpful to diagnose what is happening. The longer tubes are likely used to bypass the shim stack when the shaft is near full extension, controlling how it performs over the smaller bumps.

Unless I've been wrong for years, Fox bypass shocks use 2 compression and 1 rebound bypass tubes (unless they're the high dollar bypasses which use more tubes). The longest compression bypass is in use until the shaft is almost fully compressed, once the shim stack moves beyond the bypass tube all of the fluid goes through the stack. See my photo in my previous post.

And agree shock tuning is complicated. Getting the correct springs and preload is half of the battle.

 

[madweazl]

Maybe I'm jacked up. This is how I think it works.

 

[KLC]

That's correct.
With my Fox bypass, the shaft can move upwards with oil bypassing the shim stack until it gets to about half way where it moves beyond the first bypass tube, it will then lose the ability to bypass through both tubes and it will get substantially stiffer. When it moves beyond the longest tube all of the oil now has to move through the shim stack. That's why I previously said most bypasses get progressively stiffer the farther they compress, and travel beyond the longest bypass tube will create somewhat of a bump stop because it goes full stack at that point. But my reference was a Fox bypass, which is designed a little different than a King. So we are all correct depending on what shock we're discussing.

And if any readers are unfamiliar with the intricacies of a bypass tube, the adjustment at the end of the tube is a spring loaded seat that can be adjusted to allow more or less oil to "bypass" the shim stack based on shaft speed. The amount of control over shaft movement is insane. For an example, lets say a bypass adjuster is turned in 6 turns (that's halfway on a Fox) and driving under normal conditions the shock may not be moving fast enough to even unseat the bypass adjuster so oil is still moving through the shim stack, now you hit a huge bump and the shaft moves quickly and creates enough movement to unseat the bypass valve and allow oil to bypass the shim stack, this takes the "jarring" sensation out of the suspension until the shaft stops moving and then the adjuster will close again, the shaft will now extend and the rebound adjuster will come into play going the other direction. It's hard to describe but that's in a nutshell. With a multi tube bypass you can have different "zones" in the shock travel with different levels of dampening. It's mind blowing how much adjustment there is.

Keeping the nitrogen charged completely will keep the oil under pressure and not allow cavitation, but the nitrogen will never mix with the oil since it's on top of the floating piston. and again the piston floats in the reservoir because as the shock shaft compresses it has to displace oil, so the oil travels in and out of the reservoir depending on how much oil the shaft is displacing at a given time. Increasing the nitrogen charge makes it harder for the shaft to displace oil which is why shocks get stiffer when you put more nitrogen in them.

A coil over shock with no reservoir is called an "emulsion" shock because the nitrogen gets mixed in with the oil. It's not nearly as efficient but it still works.

Sorry for the novel, I was going to go back and edit most of it out but I left it in anyways. I DO NOT think I'm the smartest one in the room but I've had my share of shocks disassembled for rebuilding. I probably couldn't tune my own shocks to save my life though...