When it comes to a suspension for trailers above 3.5t the air becomes a bit thin. With this subject there are also a few camps supporting one or the other technology. How good does a suspension on a van need to be? Well, some people claim that only a vehicle needs a comfortable suspension and the one on a van needs to be practical and safe but not necessarily comfortable. I beg to differ, especially when one plans to go on lots of tracks.
The simplest and cheapest solution is surely the old traditional leaf spring suspension. Has a good spread of load over the main rails and can be made load sharing. But that is already about as many positive points as one can find. The leaf springs are dimensioned for the maximum load of the trailer, so are all the other non adjustable suspensions too, and will give a harder ride when the trailer is not loaded. With many vans one has only a small payload of 300-400kg, so it might not make much difference one could think. However it does on the track.
Another camp claims that vans don’t need independent suspensions and full axles are better for stability. I do not accept that concept since a full axle suspension will make a trailer roll far more than a good independent suspension.
Coil spring suspensions are per definition non load sharing and therefore less stable than load sharing suspensions.
My preference is an independent suspension for several reasons. Less roll for the van, more space between the wheels or higher clearance when sitting in a deep track. Since coil spring suspensions are not load sharing and non adjustable and usually they are limited to ATM below 3500kg anyway, the only sensible solution for me was an airbag suspension.
Adjustable and configurable (load sharing or non load sharing) and a wide range of available air springs make this suspension the leading concept. Features like auto levelling and variable ride height, parking height and maximum clearance height make this suspension more versatile than any other type. Combined with a good air management system and good dampeners (best if adjustable) the airbag suspension can be adjusted and optimised for pretty much all load and surface situations. If one uses bags, which can also run without air one can design a system which still allows limping home with a non inflated bag if re