Independent rubber suspension on offroad boat trailer???

Submitted: Friday, Sep 04, 2015 at 22:59
ThreadID: 130189 Views:8139 Replies:10 FollowUps:1
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Hi guys

I am in the process of designing a new offroad trailer for my 12 foot tinny which will also carry my roof top tent on a removable rack with legs that Jack the RTT off the trailer. This trailer is going to need to be fairly robust as I will be taking it to the Cape several times hopefully. Now don't get me wrong I'm not going to take it down shotgun, but don't want to be restricted in where I can go up there other than the simply impossible.

Getting to the point I have been looking at independent suspension for the trailer and came across Duratourque and ALKO independent rubber suspension and would like to know if anyone has given in a good workout workout? I would be adding shocks to the system but it does seem alot cheaper than traditional independent suspension setup. I was going to fabricate my own swing arms but have been put off by how easily I could bugger up some of the geometry and figure I'll be busy enough making the trailer as is.

Any advice would be great guys as have never seen IRS in the flesh


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Reply By: gbc - Saturday, Sep 05, 2015 at 05:55

Saturday, Sep 05, 2015 at 05:55
Kevlacat used alko rubber suspension on their genuine trailers with decent success. Being a cheap alternative to coils and still not picking up much market share in the camper trailer/offroad world is a worry. Trailer mobs like conqueror Australia import South African product with alko suspension, then cut it off and install their own if that's any indication. A 12 foot tinny isn't going to be as hard on suspension as a loaded camper though.
AnswerID: 589993

Reply By: Member - neville G (QLD) - Saturday, Sep 05, 2015 at 07:42

Saturday, Sep 05, 2015 at 07:42
I have used Alko suspension on both a camper trailer (Campomatic) and now my trusty Phoenix caravan. Have travelled around 150000klms. combined with no trouble to date. Have not used shock,s.
Cheers, Nev.
AnswerID: 589994

Reply By: Bob Y. - Qld - Saturday, Sep 05, 2015 at 08:17

Saturday, Sep 05, 2015 at 08:17
We had dual axle Al-Ko suspension on a gooseneck, Tosh, that we used to cart 4-5 horses around, on roads similar to what you're suggesting.

I feel you'd be better fitting some other suspension than waste your time fitting Al-Ko, or similar types of runner mounted suspension. In the long term they just won't hack it.

On bitumen, and good gravel roads, they might be okay, and ride well.


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AnswerID: 589995

Reply By: Member - Alastair D (NSW) - Saturday, Sep 05, 2015 at 09:04

Saturday, Sep 05, 2015 at 09:04
I have had Alko rubber suspension on my 2T tandem trailer for ~15 years. It has done a lot of work with no problems. Hope Mr Murphy is not listening.
AnswerID: 589998

Reply By: Ron N - Saturday, Sep 05, 2015 at 13:02

Saturday, Sep 05, 2015 at 13:02
Tosh, You didn't say, but with a 12' tinny, I presume that you're talking single axle setup, not tandem?
The second question is, what kind of total load (gross trailer mass) are you going to be looking at? I would imagine no more than about 1.25 to 1.5 tonnes?

You are right about not mucking around with building your own independent suspension. To do so, you need to comply with a heap of exacting trailer ADR's (see Vehicle Standards Bulletin VR1)

Regulations regarding the construction of trailers - VSB - VR1

To build your own suspension requires meeting many types of steel specifications, construction methods, and design limitations. In addition, to ensure you get the axles aligned correctly for minimal tyre wear, you really need to build a jig - so there goes any cost advantage of DIY.

The bottom line is you get what you pay for. If a component is cheap, it's going to have shortfalls in design and performance.
The rubber-torsion-system suspensions come in a substantial number of brands and a number of designs, besides just Duratorque and AL-KO.

They have been around since the 1950's, and they fill the bill for suspensions where substantial articulation of the suspension is NOT needed (i.e. - good roads), and where loads are moderate.

I built a 500 gallon (2273 litre) tandem fuel trailer in the early 1970's, using two of the early rubber torsion suspension axles, called PosiTorque.
PosiTorque axles are cheap and nasty and provide pretty poor performance.
Those axles performed badly in paddock work and with full loads, they would twist so badly under load or sharp cornering that the wheels adopted positive camber (splayed out).
Eventually, the trailer broke several axle stubs due to overloading of the stubs due to inability of the axles to share the load.

The AL-KO rubber torsion axles appear to be far superior to the Positorque - but at 4 times the cost. They still have an inability to articulate over a wide range, which is what is required when off-roading. The rubber torsion axles tend to ride more harshly when lightly loaded.
The rubber components of these suspensions will deteriorate faster than any of the steel components of the suspension, because that's the nature of rubber.
In addition, the rubber components of these axles are the most highly stressed component of the whole setup, they are constantly being compressed and then unloaded.

Factors that shorten the life of the rubber components in these suspensions are;

Severe corrugations.
Constant high speed travel.
Dust/grit/salt water ingress into the suspension, creating corrosion and chafing in the rubber components.

Many of these rubber torsion suspensions suffer from failure of the rubber components after a few years of hard work.
The worst part is, you can't check on their condition, you only find out when the wheels start to splay and the rubber components start to fall out.
The manufacturers state that 10-15 years is the average life of the rubber components. That means, that on off-road work, in high ambient temperatures, and on extremely dusty roads, you could get as little as 5-7 years out of them. 5-7 years is not long.

A multiple-leaf, steel spring setup with shackles is the tried and proven, low-cost suspension, for most loads and most conditions.
With a beam axle, you have limitations in off-roading as the centre of the axle will hit obstructions in the crown of the track, or cause unwanted drag in sandy or muddy conditions.

This is where swing-arm suspensions with a high level of articulation and good clearance come in, as the ideal choice for off-roading.

The bottom line is, buy the best suspension you can afford, with the best off-road load rating, so you have plenty of load margin.
Many trailers are regularly operating at near, or over their suspension load limits.

The high initial cost of a swing-arm suspension, can be offset against the fact that you won't be repairing it every three months, it will cause less damage to your boat and trailer frame, and the increased articulation and ground clearance will sometimes mean the difference between getting through, and not getting through.

There are Huntsman swing arm independent suspensions on eBay that start at $1400 for 1.25 tonne load rating.
IMHO opinion, I would seriously consider one of these as a good choice for what you are intending to do.

Huntsman Independent Suspensions - eBay

Some more advice, information, and discussions below ....

Trailer parts catalogue

Hold it Steady - Trailer axle selection advice

Caravan repair centre - Simplicity suspensions

Kiwis discussing Duratorque, AL-KO, and spring suspensions for boat trailers

AL-KO IRS suspension discussion

Cheers, Ron.

AnswerID: 590003

Reply By: Tosh A - Saturday, Sep 05, 2015 at 14:11

Saturday, Sep 05, 2015 at 14:11
Cheers guys,

Ron. Yes it will be a single axle setup and although I'm not sure of the exact weight just yet I estimate around 1200 kg wet but will run it over a weigh bridge next time I've got it fully loaded.

Thanks very much for the links I've got alot of reading to do.

I guess it's like you said I have to decide what will work and what I'm willing to cough up.


AnswerID: 590005

Reply By: Member - Scrubby (VIC) - Saturday, Sep 05, 2015 at 19:44

Saturday, Sep 05, 2015 at 19:44
G`day Tosh,

I built an off road heavy duty trailer for my 12 ft tinny earlier this year and took it on it’s maiden trip to Cape York in July.
The only trouble I had with the trailer on the trip was the dust cap on the left wheel fell off on two occasions wrecking the seals, bearings and hub each time; I reckon this was caused by stones from the road shoulder hitting the cap and knocking it off.

I planned the design for a long time before settling for what I built.

Briefly …

Highlux rear suspension , 1.2 mtr eye to eye 7 leaf springs, shackles and bushes.( long springs give a floating type ride.
50 mm square solid axle with parallel bearings.
6 stud Landcruiser Hubs, same pattern as vehicle.
15 x 7 inch gal steel wheels.
15 inch Maxxis L/T tyres.
Main chassis rails 100 x 50 x 3mm – 4mtrs long cut and bent at 2 mtrs.
Cross members 50 x 50 x 2mm.
75 x 75 x 3 mm x 3 mtr long telescopic extension draw bar.
AT35 off road coupling.
Boat runners/guides made from heavy black poly pipe glued into channel section.( this will support the boat/load full length rather than rollers that only touch a small area here and there)

All RHS sections are connected with drilled holes and will have fish oil or diesel sealed internally to prevent internal rust. ( this will be after I seal all the leaks I left when welding) LOL

Phone--" oh for too ate vive oh for too zefen nyn." if you would like a yarn about it.

I don`t know where i`m going but i`m enjoying the journey.

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AnswerID: 590014

Reply By: Tosh A - Saturday, Sep 05, 2015 at 21:10

Saturday, Sep 05, 2015 at 21:10
Hi Scrubby

Mate I will definitely give you a call in the coming days. Just a few questions, how did you come up with the hilux spring setup? does make alot of sense(used to run a jackaroo rear spring setup in a Suzuki sierra when I was 17 as you said longer spring more flex andtravel)but what year what model and do you know what load rating they are? Also did you galvanise your trailer before painting as I am also thinking about an oil fill and find paint allows for easy upkeep when doing lots of offroad work as gal chips just as easily as paint but is expensive to redo and I can paint it myself on any given Sunday and am trying to justify it to myself(I also have to drive 500km to the nearest gal place from where I am)


AnswerID: 590020

Follow Up By: Member - Scrubby (VIC) - Saturday, Sep 05, 2015 at 22:04

Saturday, Sep 05, 2015 at 22:04
I remember seeing a Malcolm Douglas doco years ago and he had an old box trailer with long eye to eye springs behind his Landrover that just seemed to "rock & roll" over the bumps and corrugations and I reckoned that it worked much better than short springs.
I forgot to mention that I am now making a fitting that will prevent the bearing caps from coming off.
I will put it on this Forum when I have it set up.

I will be pleased to hear from you.

I don`t know where i`m going but i`m enjoying the journey.

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Reply By: duck - Saturday, Sep 05, 2015 at 21:10

Saturday, Sep 05, 2015 at 21:10
Have had many types of suspension & I do like the rubber Alko etc type but as a boat builder &supplier they are normally a lot harder then a spring version & they work great on heavier craft/trailers but on lite small trailers I find there hard on the craft they do last better than std springs but they rust from the inside out & it's only when they fail you will know about it, but as a rule this takes a lot of years
There is a version comes from the USA where the swing arm can be taken off & set so on trip to the cape you can set it for high clearance & when you get back set it for std use
Good luck
AnswerID: 590021

Reply By: mack c - Sunday, Sep 06, 2015 at 02:57

Sunday, Sep 06, 2015 at 02:57
Hi, Lot of info here on Suspension.
Make sure you DO add some decent shockers to suit. Preferable two lighter sets than just one. (google it)
I've used EFS for yrs on corrugations etc on Patrols and H/Duty of road caravans.
Never once had one blow a seal.

Spend time on your trailer chassis. Lots of.
Just cause a light boat. think what you'll add to inside fuel tools etc etc.
I'd use 4mm MIN tubing or H/D angle in main frame, with decent fillet welds and gusset plates at every junction.
Over 45 yrs travelling in the bush and corrugations. the most thing you see left behind. was always trailers. Cracked chassis first. suspension second.
I'd go a non slipper leaf springs. soft rating with solid (rather than air) airbags inside coils. under centrepoint of springs to take load. with shockers to suit.
Mounted inside the suspension angle frame, they won't tend to bend chassis at that point.
Carry some fencing wire and a length of angle. You'll ALWAYS get home with leaves,
as long as your chassis in one piece.
The best suspension in the world is no good with a bleep ed frame above it.
and remember. the softest suspension travels the best over corrugations. Damping is the most important part of.

Fancy suspensions are all well and good but really. A lttle tinny?.
Building yourself it won't cost more much than a grand or so looking around
and go Galv tubing. Cold Galv sticks for weld points and I'd also go the mechanical
disc brakes on stainless cables.. replace pads regularly, they work real good and reliably
I've had them on my Stacer 525 since '02. replace pads yearly and remember to wash them and run on foot brake pedal for a while every time you come out of water.
Never missed a beat.
Or pay more and get the Bronze discs.
I've run "Bearing Buddy's" the same. Just give the inside of sleeve a tickle in coupla places with cold chisel first.
Makes them real tight. (IE a prick to remove.)

I've made a coupla boat trlrs over the yrs. Plus others.
Weld up main frame on flat concrete so no warping/stress. More diagonals than you think you'll need.
And I always make up suspension on separate H/Duty angle bars. Then balance up trailer on them. Drill locating holes and through bolt there. adding a few extra holes front and back of them for adjustment.
With ALL through bolts. buy longer than required. then drill a small hole through end behind where nut will go.
A split pin or ring, there is great mental security.
Have fun and buy plenty of rods. I prefer stick to MIG for serious welding.
AnswerID: 590025

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