Thread: Polyairs

They work well.

Just finished a trip around Oz where we were pulling a camp trailer and fully loaded 110. No sagging what so ever (ran approx 25PSI when loaded) and drop down to 5-8PSI empty.

Would recommend.

I have polyairs in mine:

It meant that I could use a "lighter" coil spring on the rear for day to day travelling so that comfort was not sacrificed. When the disco is loaded the polyairs can be pumped up to maintain ride height.

I guess that it has some impact on axle articulation but like everything it is about compromise and optimise:



If you go down the path consider the location of the valves. Mine are in the filler compartment.



That gets them out of the crap and out of harms way and they are convenient to get to. Mind you I have had some funny looks from people when I open the flap and proceed to refuel the car with compressed air. :wink:

I had polyairs on my County and echo the comment that you can keep lighter springs for a comfortable ride unladen but maintain ride height with a load.

The only thing I would add is that I found the suspension 'clunked' if they were not let down when the load was removed - I reckon the shocks (Konis but that is another story) were topping out. And also that with a load you did need to dial your shocks up otherwise it felt like you were driving a Japanese one tonner. If you keep the suspension at normal height you kept normal wheel articulation regardless of load.

I must get around to fitting them to my Discovery

I have found them a great help.


Not just for heavier loads, but I have found my disco will behave a little more predictably over long stretches of corrugation etc.

I had em on for years on my old 77.

I found them good for heavy loads , but that they really affected articulation in the mountains. The problem is that even with no air in them they take away about 1-2 inches of upward travel, like having tennis balls in the spring.
Of course with the recommended 5lbs minimum, they take away even more maybe 3 inches upward lie a big bumpstop. I never found a pinching problem and used to take the valves out off road.

So I used to take them off, and put them on. I was undecided whether they were good or bad.
One potential problem is that if you are going somewhere like crossing the Simpson then you need the heavy load AND the articulation. In this case I cannot see how to get over harder springs.

I tried all sorts of things like having a T piece in each line valve to cross link them off road so the one going up pushed the other down. I predated the 2004 rangie. But I could never get a gate valve that would hold air reliably.

But for towing a Van around Oz they are excellent.
Regards Philip A

With respect Philip,

I think that three inches is an exaggeration :wink:

See the photo above and consider that there is a sway bar in the equation as well.

Yeah , you are probably right. Who knows.
I think it depends on whether you have a lift and have the spacer. ie how much load is on the bag at normal ride height.
Just a quick calculation
They are about 9 ins high and 3 inches in diameter. My quick and dirty calculation gives the surface area at 72 square inches , plus the ends. At 5 PSI that should be 350 lbs total pressure Vs a spring at 220 lbs per inch deflection.
My Physics gets left behind here , but you can see that it takes quite a bit to deflect them and as they are progressive ie as the volume declines the pressure is higher, they will not deflect much at all ( after they belly out into the spring voids).
Your photo shows one wheel deflecting downwards and that will not be affected at all. Its the other wheel deflection upwards that is the problem.
In fact your photo shows the body being much higher than I would expect with good articulation.
Its only a real problem with no locker and extreme work. But also the ride is not as good as you get much more"head toss" as they call the sharp side to side movement caused by excessive roll stiffness.
regards Philip A

i'm not sure articulation is affected to much although i must get out of the cab one day and see if the diff is touching the bump stop, when i crossed the simpson fully loaded i was running around 20psi in the poly airs with no problems. the pics below are with the fender unloaded running around 5 psi, one would have thought in the second two pics when i was checking my articulation i would have had a look at the bump stops, maybe somebody could tell me if the rear wheel had much more upward travel into the wheel arch, if anything i think the down travel if efeect if any