Air suspension pressure (yours)

[zildjian]

Over inflation is known to make your cars own leaf springs redundant
and none of us should rely totally on air springs as a substitute as they create stresses in parts of the chassis structure not designed for them, so lets have a poll and see what works best typically

[lamp-it]

What happens with over airing the system then?

[TrueDink]

Your chassis snaps.




Mine were sitting on 75psi when this happened.

http://www.demountablecampergroup.com/v ... f=19&t=334

[keeflester]

I ain't necessarily the fault of the airbags. A full engineers investigation might show a range of causes, and in any case it might have been outside the design envelope of the chassis before the airbags were fitted.




People seem to be keen on blaming the airbags without fully understanding the problem (present company excepted).

I believe weight distribution needs to be better understood by the sellers of campers, my experience of buying from a "dealer" demonstrated a disregard for the actual suitability of the camper for the vehicle. If you are suffering from imprecise steering, heavy brake wear, porpoising and apparently overloaded rear tyres (look at the bulge), then you may be in the same boat.

Airbags will not cure any of the problems, but will be able to conceal the most obvious evidence, the down-at-the-back stance.

[sabconsulting]

I agree with the above. It is not specifically the fault of the airbags, but their application that is the problem.

My truck would sit slightly tail high unladen, but adding the weight of the camper levelled it out. I added airbags as belt and braces, but sort of regret it, and now run them at the minimum pressure - something like 6psi - I can still feel their effect though.

I assume most people have campers that weigh less than their truck's approximate 1000kg payload. So I assume most people need to add airbags not because they are overloaded, but because the camper's center of gravity is too far back for the truck - often behind the rear axle (it is in the case of my camper, but many appear much further back than mine).

Hence airbags get added to raise the rear suspension so the truck and camper sits level again. And i assume people will increase the airbag pressure until the camper sits level again. If that takes 75 psi then I would suspect the centre of gravity of the camper is well behind the rear axle in order to need that much compensation.

If this is the case I foresee a two-fold problem:

1) Pumping the airbags so high means they act almost as a fulcrum rather than a spring. If the centre of gravity of the camper is forward of the rear axle I would expect this to simply result in a very uncomfortable ride.

2) The above coupled with a centre of gravity BEHIND the axle becomes a bit like your school physics class - with weights on the either end of a ruler with something in the middle as a fulcrum. In this case the fulcrum is the airbag and the weights are the engine, front axle, transmission, cab and occupants at one end, and the camper at the other. If you did this experiment with a cheapo and brittle plastic ruler at school you might end up with a shattered ruler.

I foresee the above fulcrum affect meaning that every time the rear suspension goes over a bump, it pushes the fulcrum up, which instead of responding as the truck springs would by deforming, simply transmits the movement to the chassis with little deflection. It may therefore react by trying to lift the front of the truck, creating a porpoising effect where the front of the truck feels like it is bouncing up and down pivoting around the rear axle. This will clearly put a lot of bending force on the chassis forward of the rear axle. I suspect the truck designers will have tested the chassis in the opposite direction, but not that direction - i.e. by putting a large dynamic load in the middle between the two axles and checking the chassis does not fatigue. But I doubt they would have tested the opposite - pulling either end of the chassis down so the middle flexes upwards.

Steve.

[Bookend]

I'm now wondering if the air bags should be taken off.

The drive before fitting them was not terrible and the truck didn't sit low at the rear end the only issue was with body roll.

I would rather that than damage the truck.

[zildjian]

Well I would leave them on for what its worth,
they've given you the worse case scenario, this occurs pretty rarely and to date has been limited to Nissan,
apply air sparingly as poll shows, and our Hilux' will be fine,

Run that Mk6 with air for 3 years now as described without any ill effect,
I might also add I had the load liner out the other week (to fit a camera) and there was absolutely no distortion as a result the camper trying to launch itself and its mooring away and I've travelled across a a couple of fields and I don't mean playing fields

[TonyS]

As well as for demountable use, I regularly transport an IBC container full of drinking water for horses, this holds a cube of water, weighs one tonne, and fits exactly within the confines of the load tub with the tailgate neatly closed on my double cab Ford Ranger. Prior to fitting airbags, the truck towbar was very nearly ploughing a furrow up and down the A1, even with brand new rear springs. With airbags fitted and inflated to 25 - 30 psi I can say that the ride height has increased, handling is vastly better and I no longer attract unwanted attention from For that reason alone I would retain the airbags...

[TrueDink]

I agree. It wasn't solely the air bags fault for my mishap. Just a contributing factor. I wouldn't remove them now you have them.

[Gary W]

Air bags are superb if used correctly. They can aid roadholding and comfort, reducing roll and the effect of sidewinds and truck wash. They are also awesome for levelling the camper on site (for my money they're worth the cost for that alone!) and helpful when mounting and dismounting the camper, especially on uneven ground - but they can be catastrophic if abused. I'm a little worried that some members are using over 40 psi. Such high pressure will almost certainly cause vehicle damage and suggests the rear axle is massively overloaded. If that sort of pressure is needed it maybe a good idea to pluck up the courage to take a trip to the weigh bridge and see what you are dealing with.

With an air assisted system we find between 1.25 and 2 bar (ca. 18-27 psi) gives the best results with a fully loaded camper and the system we use has pop-off valves that ensure the resting pressure doesn't exceed 3bar (ca. 43psi). OK our campers are very light and weight distribution is a key design consideration, but even when loaded to ridiculous excess 3 bar is just too high for driving - you would normally only use such a high pressure for levelling on site. At the other end of the scale it's worth remembering that all air bags must have some pressure in them too to avoid internal damage. On our system the minimum is ½ bar (ca. 7.25 psi) but some systems require more, it's worth checking your documentation.

I don't know if that's helpful but I hope it is anyway.

Best wishes

Gary