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;
Heat.
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 catalogueHold it Steady - Trailer axle selection adviceCaravan repair centre - Simplicity suspensionsKiwis discussing Duratorque, AL-KO, and spring suspensions for boat trailersAL-KO IRS suspension discussion
Cheers, Ron.
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