Nitrogen charging shocks?

[bics90xj]

Want to check the pressure in my Fox 2.0 remote resivor shocks. What PSI should they have and where can I get a fitting to mate with the schrader valve?

 

[DieselSJ]

IIRC Fox recommends 225-250psi. Use nitrogen only! You need a nitrogen tank, regulator, and high pressure lines to do this.

 

[playwithit]

I just finished rebuilding a set of 7100's. I had a motorcycle charge them to 225lbs. They charged me 20 bucks.

 

[bics90xj]

Yeah! I found our shops Nirogen kit!

 

[ktm racer 419]

hokay, to avoid a new topic.

can someone tell me what to charge my foa 2.0 resi shocks to?


i know it says 130-180 psi of nitrogen.

but theres a nice range of 50 psi in there. would i see a different benefit to running a higher pressure over a lower pressure? and vice versa of course.

 

[Team Willys]

The higher pressure you run, the stiffer the compression will be.

 

[ktm racer 419]

The higher pressure you run, the stiffer the compression will be.

GAHHH

is it really noticeable? i know it makes sense, but i cant find any information on how much of a difference it should make and what i should run for what i do with it. all i know is that 50 psi window.

thanks though

 

[9T3XJ]

Have you tried contacting Chris with FOA? He seems pretty helpful on pirate4x4. I'm curious about this as well, been seriously thinking about upgrading to the 2.0 resi's.

 

[asp]

psi*(pi*Piston dia^2)/4=force

and

PV=nRT

n and R are constant and you don't do much high speed offroad driving for long periods of time so you can also assume that T is constant for your application. Oversimplified, P*V = constant.

You mentioned they're 12" travel. What's the wiper diameter inside? That will give you V (stroke*pi*d^2/4).

If you want to find the 'spring rate' for any given internal pressure at full extension, Do some algebraic manipulation and some differentiation and you'll find that:

k=PA*stroke/((stroke-compression)^2)
Where P is the pressure in the shocks at their extended length
A is the area of the piston in the shock
stroke is the length of the shock in its extended state
compression is how far it has been compressed

Note that this k is not constant at all lengths of travel.

Sam, do some math and figure out what your overall wheel rates need to be and adjust the pressure in the airshocks accordingly.

 

[ktm racer 419]

psi*(pi*Piston dia^2)/4=force

and

PV=nRT

n and R are constant and you don't do much high speed offroad driving for long periods of time so you can also assume that T is constant for your application. Oversimplified, P*V = constant.

You mentioned they're 12" travel. What's the wiper diameter inside? That will give you V (stroke*pi*d^2/4).

If you want to find the 'spring rate' for any given internal pressure at full extension, Do some algebraic manipulation and some differentiation and you'll find that:

k=PA*stroke/((stroke-compression)^2)
Where P is the pressure in the shocks at their extended length
A is the area of the piston in the shock
stroke is the length of the shock in its extended state
compression is how far it has been compressed

Note that this k is not constant at all lengths of travel.

Sam, do some math and figure out what your overall wheel rates need to be and adjust the pressure in the airshocks accordingly.

if you dont do the math for me i'm just gonna charge them somewhere in the middle.

and i want western valving, as i forsee myself out there in the future

 

[ktm racer 419]

Have you tried contacting Chris with FOA? He seems pretty helpful on pirate4x4. I'm curious about this as well, been seriously thinking about upgrading to the 2.0 resi's.

im just wondering how this is all figured out right now. once i actually have the shocks in my hands i'll likely give them a call

 

[vetteboy]

psi*(pi*Piston dia^2)/4=force

and

PV=nRT

n and R are constant and you don't do much high speed offroad driving for long periods of time so you can also assume that T is constant for your application. Oversimplified, P*V = constant.

You mentioned they're 12" travel. What's the wiper diameter inside? That will give you V (stroke*pi*d^2/4).

If you want to find the 'spring rate' for any given internal pressure at full extension, Do some algebraic manipulation and some differentiation and you'll find that:

k=PA*stroke/((stroke-compression)^2)
Where P is the pressure in the shocks at their extended length
A is the area of the piston in the shock
stroke is the length of the shock in its extended state
compression is how far it has been compressed

Note that this k is not constant at all lengths of travel.

Sam, do some math and figure out what your overall wheel rates need to be and adjust the pressure in the airshocks accordingly.

Do you know how reservoir shocks work?

'Cuz that's all well and good, but we're not talking about air shocks, dumbass.

Never mind the fact that you're neglecting the effect of the oil level, and how the air pressure actually affects wheel rate.

 

[ktm racer 419]

'Cuz that's all well and good, but we're not talking about air shocks, dumbass.

LOL

i was too frightened by the numbers so i didnt even read all of it

 

[asp]

Yes, I do. But I forgot that Sam was asking about resevoirs. My mistake. And yes, I was neglecting any damping.

I'm not sure how to calculate it for a resevoir shock. I could tell you how it would behave but I don't know what numbers you want to aim for.