CARAVAN RUBBER TORSION SUSPENSION

Only ever seen them on small light weight trailers. Be interesting to see how it would handle offroading. I did look at doing this on my tub trailer and was advised not to by a local trailer manufacturer. He gave me no firm reason

BB - Many years ago (a frighteningly long time ago, in fact, when I stop and count the years), I built a tandem fuel trailer, which carried a 250 gallon tank (I did say a long time ago!).

That tank was 1176 litres in todays measurements, and the trailer tare was around 700kgs.
The 1176 L of diesel weighs pretty much spot on a tonne - so gross trailer weight was around 1700 kgs.

That little tanker was fitted with "Flexitor" rubber suspension axles - essentially the same design as the Dexter suspension.
The Flexitor design has been around since 1951, in Australia.

Unfortunately, the Flexitor axles proved to be a bad choice for that little tanker - which did a lot of rough paddock work - which equates with "off-road use".

Those Flexitor axles snapped on a regular basis - the rubber inserts chewed out on a regular basis - and the whole setup was nothing but a PIA.

Essentially, it comes back simply to the fact that the Flexitor/Dexter rubber suspension system is utterly useless for off-road work - simply because of its very limited amount of swing arm articulation.

Once you run out of swing arm articulation ability, the wheel comes off the ground, and the entire load is then transferred to the other axle - seriously overloading the spindle, the bearings, and the suspension.

I cut the Flexitor axles off the fuel trailer and installed a proper, good quality, fully greasable, four spring suspension, with rockers - and that suspension is still in use, more than 35 years on.
The Flexitor suspension axles lasted less than 8 years.

The Flexitor/Dexter/AL-KO/Torflex rubber suspensions, with their very limited articulation, are cheap and good enough for bitumen roads - but you will end up a very sorry owner if you specify and fit this style of suspension for off-road work - even if it's only a single axle trailer.

Cheers, Ron.

I had the alko setup on an old and very ligth weight Jayco campervan, as mentioned above there was not a lot of suspension travel. The other thing I would wonder about is with a conventional shocker setup the damping forces of the shocker are dissipated by the movement of the oil inside the shocker which is converted to heat. I have often wondered how the damping force is dissipated in a rubber system, would the rubbers overheat chewed out on corrugations etc, I imagine it would be similar to the bushed suspension on a car but the car bushes don't have to provide the damping force as the shockers are doing that?

Several well known brands of camper trailers have used Al-ko suspension for years, including Outback Campers (Victoria) & Tru Blu Campers.

The best off road vans of all time, the Phoenix built by Barry Davidson, used the AlKo rubber suspension. There was extremely little problems with either those vans or their suspension. I doubt that the Dexter models are of lesser quality than the AlKo models.

Regarding the damping effect of the rubber suspension, AlKo do offer shockers for use with their suspension. Also if you are using AlKo you need the suspension ordered for the expected ATM of the trailer, if the capacity is way over what is required it can be a bit rough.

As for wheels being lifted off the ground in extreme conditions, this happens on most suspensions including the self levelling leaf spring setups. If you don't want it to happen then go for the Simplicity suspension which has greater articulation range than the leaf spring setups.

At the recent Melbourne Caravan & Camping Show, one of the big manufacturers is using the “rubber” suspension on some of their dual axle Off Road Vans. Sorry I can’t remember which company, possibly Lotus, but this may be wrong. When asked about it, the sales person explained that the front axle is rated to 2.5 T, and the rear axle rated to 1.5 T. It works similarly to a “lazy axle”. As the load on the front axle increases and reaches 2.0 T, the second axle starts taking up the load. The vans GVM is 3.5 T, so with the total axle weight of 4.0 T, both axles together are rated over the total GVM.

Macca.

We purchased a bogey axle goose neck, for carting horses around the station, rather than knock our truck about, doing the same job. It had Alko rubber axles, and after a couple of years doing service, the front axle collapsed.

I'd question their use on dirt roads, but might be okay for bitumen use.

Bob

I wouldn't use a rubber suspension on anything that went off smooth bitumen.

Plenty of axles have been broken on that style of suspension.
One tour man broke his "you beaut offf road trailer" axle in a dip going up to Marree a couple of years ago. Destroyed quite a bit of the trailers RHS.

Even IF you broke and axle on a trailing arm type, you or someone else, can cut it off and weld another onto the arm if need be. Saw that neceessary at Kings Canyon and they purchased and trailer axle from the Alice and cut it and welded the new section onto the trailing arm.
Can't do that with a rubber one.

All rubber suspension seems to have an axle abruptly exit an arm and that is where they break off.

Disc brakes work well with wheels, and the suspension doesn't have much to do with it, Dexter or not.

I don't like the bouncing of the wheels fitted with rubber suspension.

Macca,

Your weights don't make much sense. Vans don't have a GVM. They have a GTM (max weight on the axles) and an ATM (max all-up weight of the van standing alone on the scales. Effectively GTM plus max ballweight for that van) .

If we interpret your GVM of 3.5 tonne as the max all up weight, then your total axle weight of 4 tonne makes no sense.

If you want off road use AND a tandem axle arrangement, it would be essential, in my view, for that suspension to be load sharing. Better to stay with single axle, if you can.
No rubber suspension will be load sharing, nor will most other "independent" caravan style suspensions that use coils. I see absolutely no benefit in "independent" suspension under a caravan anyhow.

Stick with simple, reliable conventional leaves with shockers.

Cheers,
Peter
OKA196 motorhome

I don't know much about this type of suspension but it has been around for a long time. I have an old Hartley boat building instruction manual somewhere in my shed from the 1960s. It goes with their with their boat building plans. It shows you how to make a rubber suspension for boat trailers.

You start with two lengths of angle iron welded into the shape of a square tube. That was then attached to the trailer frame. A second smaller square tube, it may have been solid but I can't remember, passed through the outer one. Four lengths of round rubber were stretched and passed through the tube. When released they expanded and locked the inner tube in place.

All you needed then was a trailing arm and a wheel on each end and you were off and running.

I suppose their life span would have depended on the quality of the rubber and the owner not overloading them.

There's quite a good assessment of a number of off-road, independent suspension setups for camper trailers, in the link below.

However, note that rubber torsion suspensions don't get a mention!

This assessment is somewhat limited, though, in that it is only examining single axle setups and camper trailers, and it doesn't cover tandem suspensions, nor off-road 'vans.

Off-Road Independent Suspensions assessment

Cheers, Ron.

Thanks guys for all your input - I have decided to stay with their Control Rider TS suspension but am having disc brakes instead of drum.
Cheers