CARAVAN RUBBER TORSION SUSPENSION

Submitted: Sunday, Feb 25, 2018 at 19:49
ThreadID: 136324 Views:1393 Replies:13 FollowUps:11
I have just ordered a new off-road tandem caravan 20ft and was offered this suspension as an option. I have this Dexter suspension on both of my boat trailers and have been very impressed with it over many years but have no experience with it for off-road use.
I would like to fit discs to this van and it works well with the Dexter.
Any one out there who can offer informed advice?
Cheers
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Reply By: IvanTheTerrible - Sunday, Feb 25, 2018 at 20:05

Sunday, Feb 25, 2018 at 20:05
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
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Reply By: Ron N - Sunday, Feb 25, 2018 at 20:25

Sunday, Feb 25, 2018 at 20:25
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.
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Reply By: HKB Electronics - Sunday, Feb 25, 2018 at 20:57

Sunday, Feb 25, 2018 at 20:57
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?
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Reply By: Shaker - Sunday, Feb 25, 2018 at 21:33

Sunday, Feb 25, 2018 at 21:33
Several well known brands of camper trailers have used Al-ko suspension for years, including Outback Campers (Victoria) & Tru Blu Campers.
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Reply By: Nomadic Navara - Monday, Feb 26, 2018 at 07:55

Monday, Feb 26, 2018 at 07:55
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.
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Reply By: Member - McLaren3030 - Monday, Feb 26, 2018 at 08:24

Monday, Feb 26, 2018 at 08:24
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.

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Follow Up By: Nomadic Navara - Monday, Feb 26, 2018 at 13:46

Monday, Feb 26, 2018 at 13:46
A little nit picking here. Your last sentence is not correct. The following is snipped from VSB-01 19. (This does not imply that the van does not comply with VSB-01, it just means your calculations need a bit of trimming up.)

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Follow Up By: RMD - Monday, Feb 26, 2018 at 13:53

Monday, Feb 26, 2018 at 13:53
Macca
That info from the seller is just a salespersons talk.
It depends on how the trailer/cvan is loaded and IF the angle of arms of the rubber unit is in the position to take up the load. If it isn't, the loading of each axle is out the window.

Why on earth would you have one axle rated at less than the other, doesn't make sense.
I think the critical thing to consider about about sales staff is, "the figures don't lie but liars can figure".

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Follow Up By: Member - McLaren3030 - Monday, Feb 26, 2018 at 14:50

Monday, Feb 26, 2018 at 14:50
Thank you for the correction guys, as you said, salesperson speak.

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Reply By: Bob Y. - Qld - Monday, Feb 26, 2018 at 09:07

Monday, Feb 26, 2018 at 09:07
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.

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Reply By: RMD - Monday, Feb 26, 2018 at 14:07

Monday, Feb 26, 2018 at 14:07
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.
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Follow Up By: Nomadic Navara - Monday, Feb 26, 2018 at 14:51

Monday, Feb 26, 2018 at 14:51
I think there may be some design problems there. There was never those types of problems on the Phoenix vans that were well engineered.
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Follow Up By: RMD - Monday, Feb 26, 2018 at 16:38

Monday, Feb 26, 2018 at 16:38
Peter
It has nothing to do with being a Phoenix van or not. The design of the duspension is the factor there. Rubber suspension is cheap to make and compact and that causes it to be stated and sold as superior.
AFAIK no military or serious off road use such suspension. Caravan makers do and claim it is good. The word caravan is the operative word there.
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Follow Up By: RMD - Monday, Feb 26, 2018 at 16:40

Monday, Feb 26, 2018 at 16:40
Phoenix van makers don't engineer the suspension they just buy it and fit it.
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Follow Up By: Nomadic Navara - Monday, Feb 26, 2018 at 23:18

Monday, Feb 26, 2018 at 23:18
The engineering consists of knowing what the GTM of the van is going to be and ordering the correct setting up of the axle. It was explained in CF by Barry Davidson some time back. Although each size model of axle has a maximum specified weight carrying capacity each axle can be tailored for the maximum expected trailer weight. Getting that wrong can cause problems. If you want to know more then search cabcar's postings on CF 6 or more years back.
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Reply By: Frank P (NSW) - Monday, Feb 26, 2018 at 21:05

Monday, Feb 26, 2018 at 21:05
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.
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Follow Up By: Member - McLaren3030 - Monday, Feb 26, 2018 at 21:48

Monday, Feb 26, 2018 at 21:48
Thanks Frank, corrections have already been noted.

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Reply By: Peter_n_Margaret - Monday, Feb 26, 2018 at 23:41

Monday, Feb 26, 2018 at 23:41
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
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Follow Up By: Ron N - Tuesday, Feb 27, 2018 at 11:38

Tuesday, Feb 27, 2018 at 11:38
Peter - The "independent" suspension arrangements such as Simplicity, Kalpakoff and others, have multiple benefits.

One of the benefits of these suspensions is reduced shock loading to the frame of the trailer or 'van, when a pothole, sunken culvert, rock, or road corrugation is encountered.

A secondary benefit is that numerous styles of the independent suspension arrangement have the ability to adjust toe-in/toe-out for improved tracking and improved tyre life.
Axles, and therefore tyres, quite often get out of alignment due to hitting rocks, big potholes, kerbs - or by turning too sharply.
Axle spindles do bend, axle beams do bend, and other suspension components can become deformed - therefore, the ability to compensate by adjustments, to realign wheels/tyres, is very handy.

The independent suspensions generally have a weight advantage over conventional axles and leaf springs, with a weight saving in the independent suspensions that can amount to quite a few kilos in total.

The best suspensions are the ones that provide constant wheel contact with the ground under all conditions expected to be experienced.

The best suspensions have greaseable pivot points and wide contact areas where the pivot points are.

Watch out for systems where pins or bolts pivot on thin mounting perches or brackets - these thin perches or brackets are the first to wear and cause wheel alignment problems - and wear in the suspension leads to hammering, which is impact loading, and therefore very damaging to suspensions and trailer or 'van frames.

Cheers, Ron.
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Follow Up By: Peter_n_Margaret - Tuesday, Feb 27, 2018 at 16:14

Tuesday, Feb 27, 2018 at 16:14
"One of the benefits of these suspensions is reduced shock loading to the frame of the trailer or 'van, when a pothole, sunken culvert, rock, or road corrugation is encountered."
I agree that reduced shock loadings are an advantage, but they are a function of spring rates, not of independent suspension, in my view.
What has happened historically is that traditional leaf springs used in vans have been absolutely woeful and the promoters of the independent systems capitalised on that.
I suggest that a decent leaf system (with shockies) will outperform and be more reliable that the so called independent systems that rely on coils that have no self damping.
Bust the shockers on a coil spring system and it will be totally out of control. Bust a shocky on a leaf spring system and it will still work OK.
Just my view.....

Cheers,
Peter
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Reply By: splits - Monday, Feb 26, 2018 at 23:45

Monday, Feb 26, 2018 at 23:45
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.
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Reply By: Ron N - Tuesday, Feb 27, 2018 at 13:09

Tuesday, Feb 27, 2018 at 13:09
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.
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Follow Up By: Frank P (NSW) - Tuesday, Feb 27, 2018 at 13:27

Tuesday, Feb 27, 2018 at 13:27
Note also that Chassis don't get a mention, but Chaises do - French for chair.????LOL
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Reply By: Bosun Broome - Thursday, Mar 08, 2018 at 08:24

Thursday, Mar 08, 2018 at 08:24
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
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