OzVMX Forum
Clubroom => Tech Talk => Topic started by: John Orchard on January 10, 2013, 02:29:23 pm
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I'm experimenting with some air springing on suspension, can anyone tell what the average pressure they've used in there Fox airshox, about 35 psi? Do the Fox airshox have dual air chambers?
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You put air in the top and the bottom as there are two valves. One is for compression and the other rebound.
You generally put more in the top.
Its more like 150psi, at least 100 any way. You will need a high pressure pump as a compressor won't go high enough. I also use a special gauge so you don't lose most of it when taking the pump off.
You need to buy the book.
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You should use nitrogen in Fox Airshox, around 80lbs in the top chamber and 150 in the lower but it will vary from bike to bike depending on the suspension leverage ratio.
Both chambers are compression, the top is for the first few inches of travel and the lower for the last half of the travel.
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You don't have to use nitrogen...even Fox state in their manual that either nitrogen or oxygen can be used...as a guide , I ran in my 1978 Husky 135 in the high pressure (lower valave) and 85 in the low presuure (upper valve)...but there is a formula to work out the numbers .... you can find a copy (free) at the Thor Lawson site... I have a bicycle ( mountain bike) suspension pump which you can get at bike shops that will pump to about 400 psi... I have found this works well..
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the early models and fox mono's have only one chamber. Pressure depends on length of shock ,bike weight ,rider weight and skill level and as Johnny O said leverage ratio .Get a manual!
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Think i have manual if you give info,will look for it
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Whatever you use, DONT use oxygen. Oxygen and oil explode.I think you meant air Watto.
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Whatever you use, DONT use oxygen. Oxygen and oil explode.I think you meant air Watto.
yes air is 80% nitrogen anyway but pure nitrogen will always work better.
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Whatever you use, DONT use oxygen. Oxygen and oil explode.I think you meant air Watto.
yes air is 80% nitrogen anyway but pure nitrogen will always work better.
Exactly!
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Tried to put air into Steve Sweeny's YZ400D Fox shock & it actually went down @135lbs.
Had to put it on a stand to take the weight off it to pump it up and it still sags to about half
You need one of those high pressure pushbike pumps.
On another matter the shock will be for sale soon as I am restoring his bike back to original.
0427334186
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what bike model is it ? .you need to work out what the suspension lever ratio is first which is rear wheel travel devided by shock shaft travel ,allways set high pressure 1st it is the lower valve allways have bike on stand when adjusting presure
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Ah, the 100% Nitrogen vs 80% Nitrogen conversation is back :)
Are they Fox Airshox or Fox Nitroshox? :)
Is there really oil in the bladders? Snake oil?
Air (O2 + N2) does not behave differently from Nitrogen (N2) under pressure when it comes to the first principle of thermodynamics....
But yes, Nitrogen is much more cool :)
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Ah, the 100% Nitrogen vs 80% Nitrogen conversation is back :)
Are they Fox Airshox or Fox Nitroshox? :)
Is there really oil in the bladders? Snake oil?
Air (O2 + N2) does not behave differently from Nitrogen (N2) under pressure when it comes to the first principle of thermodynamics....
But yes, Nitrogen is much more cool :)
None of the gas shock manufacturers pressurise their shocks with air.. is that just because nitrogen is more cool eric?
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Ah, the 100% Nitrogen vs 80% Nitrogen conversation is back :)
Are they Fox Airshox or Fox Nitroshox? :)
Is there really oil in the bladders? Snake oil?
Air (O2 + N2) does not behave differently from Nitrogen (N2) under pressure when it comes to the first principle of thermodynamics....
But yes, Nitrogen is much more cool :)
haha ever rode a shock that wasnt bleed properly?
for fox shock the lower chamber is fully mixed with the oil , its called emulsion, only the upper pressure is in a bladder. Fox mono's are full emulsion .ie no bladder .Answer your question?
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Actually, I believe so, mostly. More a marketing trick than a real improvement, in my view, at least from what I can see when I do the maths (PV=nRT yadhayadha) with what is left of my physics knowledge. In truth, when I do the maths, there is a difference, but so small that it is unlikely to actually make a significant difference. But hey, I am far from being an expert in anything....
Some put a wing on the trunk of their car and they swear it makes them go faster :) No offense meant.
I have a pair of Fox Airshox to rebuild, cant wait to get to that part.
As for oil and oxygen being an explosive mixture, hmm, there is some truth in that but it seems to me not really applicable to our use cases.
I seem to remember that this is derived from the physics of the diesel engine (but will not ignite without a source of intense heat...) or the absolute necessity to never apply grease to the threads of compressed oxygen cylinders (memory from veterinary school many years ago). Thankfully the pressure in our shocks or forks can never reach the levels of compressed cylinders, by a long shot...
But hey, again... I am far from being an expert in anything....
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"Oxygen behaves differently to air, compressed air, nitrogen and other inert gases. It is very reactive. Pure oxygen, at high pressure, such as from a cylinder, can react violently with common materials such as oil and grease."
www.hse.gov.uk/pubns/hse8.pdf
Oxygen under high pressure 500-3000 psi is a very different beast from air at low pressure (like our shocks), 300 psi max.
But hey, enjoy Nitrogen if you wish :)
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Actually, I believe so, mostly. More a marketing trick than a real improvement, in my view, at least from what I can see when I do the maths (PV=nRT yadhayadha) with what is left of my physics knowledge. In truth, when I do the maths, there is a difference, but so small that it is unlikely to actually make a significant difference. But hey, I am far from being an expert in anything....
Some put a wing on the trunk of their car and they swear it makes them go faster :) No offense meant.
I have a pair of Fox Airshox to rebuild, cant wait to get to that part.
As for oil and oxygen being an explosive mixture, hmm, there is some truth in that but it seems to me not really applicable to our use cases.
I seem to remember that this is derived from the physics of the diesel engine (but will not ignite without a source of intense heat...) or the absolute necessity to never apply grease to the threads of compressed oxygen cylinders (memory from veterinary school many years ago). Thankfully the pressure in our shocks or forks can never reach the levels of compressed cylinders, by a long shot...
But hey, again... I am far from being an expert in anything....
What have you been smoking?
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I did a little research on why nitrogen is better than air..
Unlike air, nitrogen does not retain moisture and thus is not susceptible to sudden changes in temperature which can cause a change in pressure.
Typically a shock pressurised at 140lbs with air can increase to as much as 160lbs at the end of a moto where as nitrogen would only increase around 5lbs. That is a fair increase in airshocks when air is the spring.
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I did a little research on why nitrogen is better than air..
Unlike air, nitrogen does not retain moisture and thus is not susceptible to sudden changes in temperature which can cause a change in pressure.
Typically a shock pressurised at 140lbs with air can increase to as much as 160lbs at the end of a moto where as nitrogen would only increase around 5lbs. That is a fair increase in airshocks when air is the spring.
plus moisture (water) is abrasive and will wear out your shock
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How about we quit the aggro, there's been half a dozen conflicting versions of fact and various poor descriptions in this one short thread already. How about explaining upper and lower chambers vs high and low pressure.
Happy new year, we're talking about 35+ yr old dirt? bike shocks not the latest cancer treatments.
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How about we quit the aggro, there's been half a dozen conflicting versions of fact and various poor descriptions in this one short thread already. How about explaining upper and lower chambers vs high and low pressure.
Happy new year, we're talking about 35+ yr old dirt bike shocks. Lighten up, we're talking about 35-ish yr old dirt bike shocks not the latest cancer treatments.
Are you the new moderator? You're gunna be fukn busy! ;D
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[quote ;Dauthor=JohnnyO link=topic=27130.msg264724#msg264724 date=1357893936]
How about we quit the aggro, there's been half a dozen conflicting versions of fact and various poor descriptions in this one short thread already. How about explaining upper and lower chambers vs high and low pressure.
Happy new year, we're talking about 35+ yr old dirt bike shocks. Lighten up, we're talking about 35-ish yr old dirt bike shocks not the latest cancer treatments.
Are you the new moderator? You're gunna be fukn busy! ;D
[/quote]
No chance of that, I reckon half the shitfights on here are overdue. ;D
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Unlike air, nitrogen does not retain moisture and thus is not susceptible to sudden changes in temperature which can cause a change in pressure.
Thats what I was going to say. Use Nitrogen It's dry, clean and stable.
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ok lower chamber hight pressure in bladder no oil unless blader has hole. upper chamber oil and lower pressure =emulsion means no piston or blader seperating oil from air, allways have bike on stand [wheel off ground] adjust high pressure 1st this is the lower chamber [shaft end] then adjust low pressure upper valve . things you have to know 1 what bike weighs 2 what you weigh with riding gear 3 what the bikes suspension lever ratio rear wheel travel divided by shock shaft travel = SLR . johnnyo is right about the air versus nitrogen air expands more with heat and the mosture rusts parts anything else you want to know just ask i have two bikes with these shocks
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and when you hav decided what you ar going to do, vmxoutlet have got all the parts you require! Check them out, they have lovely kit!
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I did a little research on why nitrogen is better than air..
Unlike air, nitrogen does not retain moisture and thus is not susceptible to sudden changes in temperature which can cause a change in pressure.
Typically a shock pressurised at 140lbs with air can increase to as much as 160lbs at the end of a moto where as nitrogen would only increase around 5lbs. That is a fair increase in airshocks when air is the spring.
Numbers great! This is where the truth is to be found :)
I would love to see the math. Seriously.
The Specific Heat and Gas Constant values for Nitrogen (N2) and Oxygen (O2) are different (see here: http://www.engineeringtoolbox.com/spesific-heat-capacity-gases-d_159.html) but not that much.
With 1/4 of an air volume being O2 and the rest being Nitrogen N2 (with small amounts of water vapor, unless you live on the west coast of Ireland), the differences in SH and GC are then 3/4 smaller even.
My guess-timate is that Pressure and Temperature of either gases in a shock absorber at work are likely to be quite similar (and possibly hard to detect without measuring equipment). For where I stand, right now, Nitrogen or Air seems to be a personal choice, but that is just me.
But I would love to see the math, or actual measurements (like temperature of the shock at the end of a race, one with air, one with Nitrogen), seriously. But won't loose sleep over it :)
I also hear that Nitrogen is better for tires... oh rats, here is another conversation coming :)
Here is a good chat about this: http://www.thumpertalk.com/topic/936969-shock-pressure-nitro-vs-air/
I suggest you red those that show actual numbers... ;)
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I did a little research on why nitrogen is better than air..
Unlike air, nitrogen does not retain moisture and thus is not susceptible to sudden changes in temperature which can cause a change in pressure.
Typically a shock pressurised at 140lbs with air can increase to as much as 160lbs at the end of a moto where as nitrogen would only increase around 5lbs. That is a fair increase in airshocks when air is the spring.
Numbers great! This is where the truth is to be found :)
I would love to see the math. Seriously.
The Specific Heat and Gas Constant values for Nitrogen (N2) and Oxygen (O2) are different (see here: http://www.engineeringtoolbox.com/spesific-heat-capacity-gases-d_159.html) but not that much.
With 1/4 of an air volume being O2 and the rest being Nitrogen N2 (with small amounts of water vapor, unless you live on the west coast of Ireland), the differences in SH and GC are then 3/4 smaller even.
My guess-timate is that Pressure and Temperature of either gases in a shock absorber at work are likely to be quite similar (and possibly hard to detect without measuring equipment). For where I stand, right now, Nitrogen or Air seems to be a personal choice, but that is just me.
But I would love to see the math, or actual measurements (like temperature of the shock at the end of a race, one with air, one with Nitrogen), seriously. But won't loose sleep over it :)
I also hear that Nitrogen is better for tires... oh rats, here is another conversation coming :)
Here is a good chat about this: http://www.thumpertalk.com/topic/936969-shock-pressure-nitro-vs-air/
I suggest you red those that show actual numbers... ;)
You should be running one of the big shock companies because they've obviously forked up using nitrogen. The stuff i quoted was straight from a shock manufacturers website.
You keep using air and i'll stick to nitrogen thanks..
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[/quote]
Numbers great! This is where the truth is to be found :)
I would love to see the math. Seriously.
Nitrogen or Air seems to be a personal choice, but that is just me.
But I would love to see the math, or actual measurements (like temperature of the shock at the end of a race, one with air, one with Nitrogen), seriously. But won't loose sleep over it :)
I also hear that Nitrogen is better for tires... oh rats, here is another conversation coming :)
I suggest you red those that show actual numbers... ;)
[/quote]You should be running one of the big shock companies because they've obviously forked up using nitrogen. The stuff i quoted was straight from a shock manufacturers website.
You keep using air and i'll stick to nitrogen thanks..
[/quote]
Yer he could be running a SX or GP team , imagine the budget savings not having to lug those silly nitrogen bottles around.If only Moose knew he could have had a bigger BBQ gas bottle installed in the Ohlins truck where the silly n2 bottle was. Now theres an idea ! How about BBQ gas , everyone s got one of those. Geez ::)
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Yeah, Makes you talk funny!! ;)
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Anyone tried Helium ?
Helium helps you jump further!! ;D
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Specific heat is the amount of heat(in kJ) required to change temperature of one kilogram of a substance by one degree. Specific heat may be measured in kJ/kg K or Btu/lboF
Hydrogen comes out on top.
Air 0.718
Nitrogen 0.743
CO2 0.655
Helium 3.15
Hydrogen 10.16
Helium is not so silly as it sounds and looks worth a try, don't think hydrogen comes in a bottle. ;D
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Interesting stuff,
This straight from the manual in front of me.
CR250 78-79 Lever ratio is 1.8. The bikes weight is 215lbs ready to race, me with my gear on is 170lbs or around 80kgs Air pressures should be bottom 128psi and top 85psi and always fill bottom first with shocks fully extended. They also recommend to over inflate by a little and reduce with a good gauge. Then ride bike for one to two minutes then recheck they will be down 15-20 percent if they have been rebuilt or deflated completely.
What the other guys are saying is spot on, it depends on the lever ratio of your bike your bikes and your weight as well.
Tell us what bike it is and if its in the manual l can give you a starting point.