[wfoerk]

Hey all,
I have a habit of checking the air pressure in my Fox DHX 5.0 every time I ride it. Am I being too anal? It's on a 2006 Glory so I have to remove a shock bolt each time, so that's the main reason I'm wondering if it's necessary. Anyhoo, thanks for the input.

 

[WestCoastHucker]

if the pressure doesn't have a habit of changing on you, you should be able to notice a difference just riding it in circles for a minute...

so, imo, yes, too anal...

 

[IH8Rice]

are you jsut connecting the hose and checking the pressure that way?

 

[wfoerk]

are you just connecting the hose and checking the pressure that way?

Yeah, and I realize I'm losing air every time I hook up the shock pump. I have this idea that ambient air temperature will affect the air pressure in the shock, so I set it every ride to start with the same pressure.

 

[HAB]

Yeah, and I realize I'm losing air every time I hook up the shock pump. I have this idea that ambient air temperature will affect the air pressure in the shock, so I set it every ride to start with the same pressure.

It doesn't. The IFP chamber has rigid walls. Ambient pressure is irrelevant.

 

[Steve M]

It doesn't. The IFP chamber has rigid walls. Ambient pressure is irrelevant.

Well he said ambient temperature which is technically correct... but when you ride the shock heats up WAY above ambient temp anyway. The differences caused by changes in ambient temperature will be too small to notice or accurately compensate for with a shock pump anyway - wouldn't worry about it mate.

 

[wfoerk]

Well he said ambient temperature which is technically correct... but when you ride the shock heats up WAY above ambient temp anyway. The differences caused by changes in ambient temperature will be too small to notice or accurately compensate for with a shock pump anyway - wouldn't worry about it mate.

Alright, thanks guys!

 

[HAB]

Err yeah I just had a brain fart reading that. I read it as pressure, not temperature.


In either case, it's irrelevant in the grand scheme of things.

 

[kidwoo]

The IFP chamber has rigid walls. Ambient pressure is irrelevant.

Not true. Even with rigid walls, the piston itself is moveable and effected by shaft position, which can and does see the effects of ambient pressure. The shock is most certainly compressible..........at the air chamber.

 

[HAB]

You're totally right. Thing is, the amount the shaft is going to move due to ambient pressure with the spring and IFP opposing it is fvcking TINY.

Edit: atmospheric pressure is like 14 psi, and the area on which it acts is just basically the end of the damper shaft, for the purpose of compressing the shock. This area is way smaller than the area of the IFP, and the pressure in the shock is at least close to an order of magnitude higher than atmospheric. Even if you put the shock in a vacuum it won't do much, even neglecting the spring.

 

[kidwoo]

I'm not necessarily even talking about movement. (poor wording on my part, I'm trying to keep it simple) I'm just talking about pressure. Say you fill a shock at 10k elevation. That's going to have an ambient pressure of less than one atmosphere at 'top out' to keep the shaft there. When you drive to sea level (roughly one atmosphere) there's a greater pressure on that shaft wanting to compress it (or in more direct terms 'helping' you compress it). The the effect is that your suspension feels softer. You've never noticed that coming down out of the mountains?


edit: saw you changed your post

 

[HAB]

Yup. I get what you're saying, and you're right in theory. I'm just saying that at least with my quick mental math approximation the effect is so small as to be totally negligible.

 

[motobutane]

Hey all,
I have a habit of checking the air pressure in my Fox DHX 5.0 every time I ride it. Am I being too anal? It's on a 2006 Glory so I have to remove a shock bolt each time, so that's the main reason I'm wondering if it's necessary. Anyhoo, thanks for the input.

Not dumb at all, ambient - smambient! I like the fact that it is on the verge of being extreme/OCD type tendencies!!! Check it twice - seriously check it when you finish a ride and buy a digital shock pump
and record the pressure and keep a log.

 

[gemini2k]

I'm not necessarily even talking about movement. (poor wording on my part, I'm trying to keep it simple) I'm just talking about pressure. Say you fill a shock at 10k elevation. That's going to have an ambient pressure of less than one atmosphere at 'top out' to keep the shaft there. When you drive to sea level (roughly one atmosphere) there's a greater pressure on that shaft wanting to compress it (or in more direct terms 'helping' you compress it). The the effect is that your suspension feels softer. You've never noticed that coming down out of the mountains?


edit: saw you changed your post

Yes, but sea level is ~14psi. 10k vert feet is about 10psi. In a high pressure shock, 4psi isn't gonna make much difference. In a high volume fork though, it will.

 

[kidwoo]

Yes, but sea level is ~14psi. 10k vert feet is about 10psi. In a high pressure shock, 4psi isn't gonna make much difference. In a high volume fork though, it will.

I didn't say it was great, I said it was present

 

[Da Peach]

 

[HAB]

Yes, but sea level is ~14psi. 10k vert feet is about 10psi. In a high pressure shock, 4psi isn't gonna make much difference. In a high volume fork though, it will.

Plus as I noted above, in the case of a coil shock with an IFP you're not even going to experience a 4psi difference in the shock with a 4psi chance in ambient pressure. You only increase the pressure in the chamber by compressing the shock, and in order to do that, you have to oppose the spring, and you're doing it with a smaller area than the IFP itself. It is iffvckingrellevant.

 

[JohnnyC]

I didn't say it was great, I said it was present

It's about the same as changing preload because the force of gravity from the moon acting on you when it is in the sky makes you weigh less

 

[kidwoo]

It's about the same as changing preload because the force of gravity from the moon acting on you when it is in the sky makes you weigh less

What you can't feel that either?

Jeesh. You guys are so insensitive.

 

[staike]

Yeah, and I realize I'm losing air every time I hook up the shock pump.

Wrong. You don't lose any air. When you connect the hose to the shock some of the pressure from the shock leaks into the hose on the pump, if it's an IFP and you set it to i.e. 150 psi, you will probaably not read more than 100-120 psi when you connect the pump. Same thing when you remove the pump, the "pssh" sound is just pressure from the hose.

 

[w00dy]

I check mine if there is a time lapse. They bleed a little pressure over time. It is possible that a morning and midday ride will be different enough in temp to make a notable difference.

 

[rockofullr]

Pretty sure shock pumps read "gauge pressure" not "absolute pressure" so your pump's reading will change based on atmospheric pressure.

Yur gonna need a properly calibrated barometer and a calculator before you can get an accurate absolute pressure.

 

[-BB-]

Wrong. You don't lose any air. When you connect the hose to the shock some of the pressure from the shock leaks into the hose on the pump, if it's an IFP and you set it to i.e. 150 psi, you will probaably not read more than 100-120 psi when you connect the pump. Same thing when you remove the pump, the "pssh" sound is just pressure from the hose.

Doesn't that assume that he is re-pumping it every time?
So if he hooks it up, then removes it, then hooks up, then removes over and over some pressure is lost to the hose. Though obviously in real life he would pump it back up as the pressure went down. I think that was his point though.

 

[daisycutter]

so true

 

[SacredYeti]

If it ain't broke, don't fix it.