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Pumping up bags (polyaire or Firestone)

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  • #1

    Pumping up bags (polyaire or Firestone)

    With my old polyaires in std springs I probably didn't set them correctly as I used to load car then pump up the bags to suit load.

    I've now got a lift and new Firestone bags and have read I'm meant to pump first then load.

    How do I guess the pressure ? I run 8psi around town . should I just start at 15 or 20 and play from there assuming if I need more its better from mid range than from low pressure to avoid any damage to bag ? This trip is just a moderate loaded car with no trailer .
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  • #2
    That seems an odd way to do it. I load the car then pump the bags until she measures correctly, underside of guards to rims. That way she's sitting as the wheel alignment was done so the caster is correct.
    Fully loaded inside and 180-200kg on the ball she usually takes around 60psi. (That's a 90 with stock springs)
    Takes a few goes until both sides are reading the same. Pump one side up and then the other then reads low but I get there eventually.

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    • #3
      You guys are doing it wrong!

      If you're planning on carrying a heavy load, you pump them up first.

      Perhaps till you get you're eye in on usual pressures I'd suggest you start full (30psi I recall?), load her up and then reduce pressures last...
      Cheers
      Micheal.

      2008 GXL D4D Auto. GOING... GOING... GONE
      2015 GXL 1GD Auto. And it begins again...

      Comment

      • #4
        Originally posted by 120D4D View Post
        You guys are doing it wrong!

        If you're planning on carrying a heavy load, you pump them up first.

        Perhaps till you get you're eye in on usual pressures I'd suggest you start full (30psi I recall?), load her up and then reduce pressures last...
        cheers, yeah i thought pump up then reduce to find the good spot. Once i've got a couple trips in different configurations done, i'll figure what pressure for what setup of car/trailer weights..

        Comment

        • #5
          Due to the non-expanding nature of helper airbags (i.e. they are not bellows), you will need to pump up the airbags prior to loading.

          In very simplistic terms, there's actually some maths behind all this.

          The area of the top of the airbags is approx. 18in^2
          The pressure inside the airbags determines how much load it will carry.
          So at 30psi, the each airbag will support 18x30=540lb (245kg) and stay at the same unloaded ride height.

          This means that to keep the same ride height when you add 490kg to the unloaded weight, you will need 30psi in the airbags.

          Summary table (pressure is for each airbag, load is right on top of and spread across both airbags and are ballpark estimates)
          10psi = 163kg
          15psi = 245kg
          20psi = 327kg
          25psi = 409kg
          30psi = 490kg
          etc

          Note that a 200kg towball weight does not translate to 200kg at both airbags. It is more than that due to leverage.

          Comment

          • #6
            I'll give it a try. No idea if 30psi unloaded will be enough but guess I'll find out.
            I know 50-60psi loaded is good, but how that translates to empty is anyone's guess.

            Comment

            • #7
              Originally posted by carco View Post
              I'll give it a try. No idea if 30psi unloaded will be enough but guess I'll find out.
              I know 50-60psi loaded is good, but how that translates to empty is anyone's guess.
              When empty, there should be a minimum pressure of 5psi.

              Comment

              • #8
                Originally posted by amts View Post
                When empty, there should be a minimum pressure of 5psi.
                5 - 30 psi is the range for firestone and polyair's standard range I believe.

                Carco what bags are you running that need 30psi unloaded?
                That is a massive amount of pressure compared to the 120 and 150 series standard bags.
                Cheers
                Micheal.

                2008 GXL D4D Auto. GOING... GOING... GONE
                2015 GXL 1GD Auto. And it begins again...

                Comment

                • #9
                  I have Airbagman.
                  Don't know what pressure they sit at when unloaded as I have always pumped them up after she's loaded and that's 50 to 60psi to get her true, flairs to wheels dimensions.
                  When driving just as a car, I let the air out of them and they shrink right away from the bumps stops etc.
                  They definitely "bellows" up when you add 10 psi, car rises too so I'll also have to give her a try with minimum pressure, say 5psi when using for everyday driving.

                  Comment

                  • #10
                    How far away does it get from the bumpstops?

                    Comment

                    • #11
                      Originally posted by amts View Post
                      How far away does it get from the bumpstops?
                      Have done my back in so can't check.
                      But she sits on 30mm spacers above the rear coils so perhaps that's where my gap's happening? Not sure how the previous owner did the install either, presume the factory bump stop (inside the coil) would have been trimmed away making room for the bag.

                      Comment

                      • #12
                        I have used Firestone Airbags for many years. The instructions for Firestone actually say you can increase air pressure after loading as opposed to Polyair. However I raise the pressure first and then load. It takes a bit of guess work and trial to find the best air pressure. I look at the best pressure to provide the best ride. My wife will let me know when it is uncomfortable. For interest, I carry some 50 - 60kgs in the back of the car and attach the caravan, about 240kgs ball weight, and I set the air pressure at 19psi. I tried 20psi, a little too firm, 18psi, a little too soft. Yes it makes a difference. I am looking for a controlled ride without a sharp response or a bouncy spring response. Depends on how much you are loading. With my Camper Trailer I use about 13psi. It is just trial and error until you are satisfied with the ride.

                        Regards

                        Garry
                        2008 GXL D4D Manual, ARB Delux Winch Bar, IPF XS800, Dual Batt, 50 mm Kings + Bilsteins, Firestone Airbags, TJM Bashplate, GME TX3420, Trak Tech drawers + cargo barrier, LongRanger 21lt water tank, Rhino Rack, Airtec Snorkle, ARB Compressor, Polaris Awning, DP Chip, 2.75" Beaudesert Exhaust, 12000lb Runva Winch

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