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Thread: Re-Gassing a rear shock

  1. #1
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    Re-Gassing a rear shock

    Hey up
    I have now worked out that I am tooo fat for my DRZ rear shock - I am in the process of getting a firmer spring (6kg per mm) and while I am at it giving the shock a coat of looking at. The oil is now chucked would anyone recommend a shock oil weight to suit a DRZ 400 and last question that may be very techy is - - Nitrogen is the prefered gas for shocks (it is inert, dry and dosent warm up like comp air) but I have Argon handy - Has anyone filled a shock with argon ??
    Thanks if yer know owt

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    I can see you, in that shed.........speak to Firefox, you don't want a nasty accident
    JohnnyBoxer



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    I see the old stories about nitrogen haven't gone away. JJH

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    Thanks for your concerns Johnny.
    I used to do all the Pressure testing on vessels and boilers for my old company Cadburys for 25+ years The bladders on these shocks dont get much past 150 psi
    So what are the old stories on nitrogen JJH ?

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    Good to hear it, we're in safe hands
    JohnnyBoxer



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    The main reason for my questions are
    1 I like to do it myself if a can
    2 I can buy but prefer not to, wherever possible, cos I live quite close to Yorkshire I am a tight bugger (but not IN Yorkshire
    3 It entertains me and keeps me in the shed and not out of it
    4 I have Argon and dont have Nitrogen handy
    5 Rotherham/nearest I can find (12 mile away) want 25 quid for 2p worth of nitrogen and that pisses me off see 2 above
    6 Hopefully this will help other folks on this wonderful informative site
    Still need opinions on what weight oil to use ( I think Its 5 )
    Thanks

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    jeez Mick you never lost it .
    Phil

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    Without opening a whole hornets nest I will just point out that 80% of atmosphere is nitrogen already and a bit of oxygen and carbon dioxide + a few other bits and pieces. Just by filling up with compressed "air" you will have mostly nitrogen anyway. Another thing was mentioned was the resistance or springiness of the gas. I think there's a mathematical formula that stats that for a given volume if you decrease the the size of the chamber you increase the resistance by a given proportionate amount and that works on most gasses till you compress them so much that they turn into liquid. JJH whoops hornets nest opend

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    My two-pennorth, as a chemist who has rebuilt a couple of shocks in the past:

    Don't use air, as the oxygen content may react with suspension components causing corrosion, deterioration of polymers, worst case (theoretical) explosion by reaction with oil.

    The advantages of nitrogen are 2-fold: firstly it is inert to most materials; secondly it has a very low diffusion/permeation coefficient (i.e. it doesn't leach out through the rubber bladder). This is the basis of using nitrogen in racing car tyres.

    The compression characteristics of most gases are described by Boyle's law, which states that pressure is inversely proportional to volume at constant temperature. There will be no difference in the behaviour of nitrogen or argon.

    Argon is even more inert than nitrogen, so no trouble there. However, it will diffuse through the bladder more quickly (by a factor of maybe 5, depending on what exactly the bladder is made of).

    So, my advice would be to go for it with the proviso that it may need re-gassing sooner than if you had done it with nitrogen.

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    Sir as someone who left school at 15 with no qualifications I must bow to your superior knowledge. Could you please answer me this? How much "air" would "leach" from the racing car tyre in the approx 2 hours of a race given given nitrogen comprises 80% of the total which won't leach? JJH

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    Quote Originally Posted by JJH View Post
    Sir as someone who left school at 15 with no qualifications I must bow to your superior knowledge. Could you please answer me this? How much "air" would "leach" from the racing car tyre in the approx 2 hours of a race given given nitrogen comprises 80% of the total which won't leach? JJH
    No idea - depends on a lot of things including thickness and composition of the rubber, air pressure and temperature.

    Here's a table of relative permeation rates, which would be a starting point: LINKY

    Do you need to know for a reason or are you just on a wind-up?

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    [QUOTE=Cook1e;4137128]No idea - depends on a lot of things including thickness and composition of the rubber, air pressure and temperature.

    Here's a table of relative permeation rates, which would be a starting point: LINKY
    Not on a wind up. Just got a pain in my neither region listening to people talking shite about the benefits of nitrogen in their Honda 50. I do sometimes get on my high horse. Obviously you know what you are talking about and your argument in favour of nitrogen in the shock makes sense. It does not convince me about any benefit in nitrogen in bike or car tyers. Thanks for your answer. JJH

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    Quote Originally Posted by JJH View Post
    Not on a wind up. Just got a pain in my neither region listening to people talking shite about the benefits of nitrogen in their Honda 50. I do sometimes get on my high horse. Obviously you know what you are talking about and your argument in favour of nitrogen in the shock makes sense. It does not convince me about any benefit in nitrogen in bike or car tyres. Thanks for your answer. JJH
    Ok, I now know where you're coming from - my line about nitrogen in tyres was not really thought through, though the rest of it is correct. It seems there are 2 other reasons for nitrogen in tyres - it doesn't change pressure with temperature as much as air (not sure why and I can't be arsed to look it up) and it's dry, whereas normal air-line air contains moisture.

    The AA seem to have a good handle on it from a layman's perspective: LINKY

    This means you're right, it's bollocks under normal road use.

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