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Spare tyre inflation pressure and weight

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  • Spare tyre inflation pressure and weight

    Would there be a significant difference in weight between a spare tyre inflated to say, 12PSI as opposed to say, 36PSI ?

    I was never very good at physics, but it might make the difference in storing a second spare on the roof as opposed to in the back.

    Thanks,

    Renth
    NP DiD Auto GLX, Front - Lovells HD Springs/Bilstein Struts, Back - Lovells SD Springs/Lovells Shocks, Polyairs, Alloy bull bar, Sidesteps, Tow bar, Rhino roof rack.

  • #2
    There Wouldn't be a significant Difference of weight between two. Try putting Helium gas in your tyres where it would be allot lighter than Normal Compressed air. I have seen some tyre shops give you the Option to Fill your tyres up with Helium, But it does cost you extra

    So putting your spare on the roof with 36PSI shouldn't affect it in weight differnece
    NJ Shortie 3ltr
    ARB Bullbar, ARB Front and Rear Air Locca, polyair bag suspension, Airtek snorkel, Dual Battery setup, Exhaust setup, Big Doof Doof Stereo

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    • #3
      The weight of the compressed air in the tyre will make SFA difference, compared to the weight of the rim/tyre combo.
      Cheers, John.
      LC200 V8 goodness

      MY12 LC200 GXL 4.5Lt V8 twin turbo, GVM upgrade, ARB bar, Warn winch, Outback Acc rear bar and dual carrier, TJM sidesteps, Bushskinz, Long Ranger 180Lt tank, Black Widow drawers, cargo barrier, Polaris Awning, +++
      Ex - NM auto, 2"Kings, Bilsteins, Buckshots, Wildcat headers, 2.75" Mandrel bent exhaust, Injected LPG, Smartbar, Scraper bar, Bushskinz, Custom steps, Dual Batteries, Breathers, Black Widow drawers, Polaris Awning.

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      • #4
        Ok so I felt like a challenge - or what ever you call it!

        Air apparently weighs in at 1.3 kg/cubic metre at sea level or 1 atmosphere pressure (14.65 psi).

        Given that "interesting"fact I calculated the volume of air in my Pajs tyres (235/85R16's) which came out at around 0.0886 cubic metres or 88.6 litres.

        Given the weight of air and the volume of one tyre I worked out that at 14psi the tyre holds just 115 grams of air. If I were to increase the pressure to 36 psi then I have crammed in a whole lot more air but the calculation says the weight of air has increased to 296 grams (an increase of 181 grams).

        So the previous answer is on the mark - it makes SFA difference.

        In fact given that 1 ml of water weighs a gram - if you drank a small glass of water befor heading off (say 250ml) you will be adding more weight to the vehicle than the extra 22 psi weighs in the tyre.

        Personally I'd be more worried about the important things like - beer tastes better out of a bottle but aluminium cans weigh less and take up less rubbish space - should I buy stubbies or cans.................

        Cheers, Lambie
        NJ 1996 ITD GLX (poverty pack) with a couple of extras, ARB bar, dual batteries plus redarc, Glind shower, some roo spotties, running 235 85 R16 AT's for the road and MT's for the tracks, tweeked torsion bars, Free wheeling front hubs, Poly airs and prodegy electric brakes for the camper, GME radio thingy, Long range tank, cargo barrier, have I really spent all this on my bus??

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        • #5
          Originally posted by Lambie View Post
          should I buy stubbies or cans.................

          Cheers, Lambie
          Cans
          Dave
          NX Pampas Cat GLS MY16
          Member 1228 Pajero Club

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