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Join Date: Dec 2010
Location: Australia, down south, Melbourne, then slightly west to, Geelong
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Suspension for an offroad Tandem Trailer

12/14/2010 6:03 AM

I am extending an off road trailer and want the ride quality, long springs provide. I'm gearing up for another 16,000kms of corrugations and 10,000kms of bitumen with a wife and three kids in tow. The trailer is heading for 5.5m and 2 tonnes Gross with a single longish drawbar. The current trailer has five foot springs off a mid 70's Falcon station wagon and provides a superb ride, albeit with about a meter of travel. I've fitted shockers, but the angle probably makes them ineffective.

So my conundrum... The independent suspension from Alko, or the like is just too expensive. $3600 for four wheels, so that's out. Rocker / Roller tandem spring setups are too rigid. (short springs). Putting two ford ute springs end on end, creates a very long trailer that wont turn, load sharing aside. I have plenty of front ends off Range Rovers, but fitting the radius arms to square axles, along with the spring sets, is a asking a bit much.

Where does this leave me?

What thoughts are there, on using two ford ute spring sets, but having the second set start inside the first set so the wheels are at a normal distance apart. I'm not sure if loadsharing really matters. If one set bottoms out, the spring will hit the bump stops and the weight will all be on the axle. The axles are rated to take the entire load, the tyres would struggle, but for short periods at low speeds, should it matter?

Further I am thinking of putting air bags on the front set to cope with fuel and water as it comes and goes and the back set I am thinking of putting sway bars. Shockers on all, probably foam.

The drawbar I'm thinking 100x50x3mm rectangular box, with 50x50x3mm angle welded with the two leading edges against the box section.

Over to you all.

Thanks

Geoff

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#1

Re: Suspension for an offroad Tandem Trailer

12/14/2010 8:28 AM

I'm not much good at building conundrums, or other musical stuff either.

But, tcmtech, who hangs out here has built some pretty cool stuff like this. He might have some ideas.

Good luck.

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#2

Re: Suspension for an offroad Tandem Trailer

12/14/2010 4:02 PM

Ok, I'll start by referring you to some documents that you should be aware of when it comes to building modifying a trailer in oz.

That said, if you are looking to uprate the load capacity of the trailer you could retain the leaf spring system. Utilise the rear spring from a Landcruiser Ute H/FJ 45/75 which are as long if not longer than a XA/B/C falcon wagon spring but with twice the capacity. You will need to replace the axle to one which is 65mm and ensure that it is turned to suit Falcon bearings. That's important, as holden bearings are only good for 3/4 tonne per side the falcon is good for 1 1/2 tonne a side.

You then get hubs to suit the rims you want to use, I suspect as you have Range Rover bits scattered around you'll be using those rims. That way you can retain the single axle setup and still carry the weight.

My $6million dollar box trailer has that setup, it has a 8'*4' box with a longish A frame draw bar made from 50mm*50mm*6mm RHS with 50mm*50mm*6mm Angle stitched underneath. I had 100mm*50mm*5mm single draw bar on it previously but wasn't happy with the flexing when fully loaded. I've carted some fearsome loads with that trailer over some very ordinary roads, I've lent my trailer to friends knowing that they won't break it. The current incarnation of the trailer has been in service for 6 years, on the same set of bearings and the second set of tyres..

Now if you want to do the tandem axles and you were thinking of air bags on the front, for a little more aggro do the airbags on both the front and rear sets. Then let the pnuematics deal with the load sharing. That would be kosher on the rego front.

I had thought of doing that for a car trailer project, with the benefit of dumping the air out of the bags to lower the trailer for loading/unloading. You will need a suitable (electric) compressor and reservior(tank) which are all easy off the shelf stuff.

One thing though is the brakes if you are carrying any sort of weight (and it looks like you are) then you'll need to consider the options. My preference is for overide hydraulic brakes much better in practice than electric brake IMHO. If you are using your Rover front end bits with Disks then hydraulics is easier. Do both axle sets with brakes.

Hopefully that will give you somewhere to start from.

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Participant

Join Date: Dec 2010
Location: Australia, down south, Melbourne, then slightly west to, Geelong
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#5
In reply to #2

Re: Suspension for an offroad Tandem Trailer

12/15/2010 5:24 AM

Thanks for the info Tob', they were excellent links. I'm a bit concerned with a single axle with all that weight. Going over sand with the weight spread over four is likely to be more successful... I think. I have ford bearings, so that's good news, always wondered what the difference was.

As per the pictures you can see the current iteration only has a smallish cross sectioned brawbar that pulls near a tonne and a half. It flexs, but hasn't failed. Am interested to hear what you have been through though.

I read up on the reg's, re airbags only on one axle set. Didn't realise this might be a roadworthy issue.

As for brakes, I'm already set up with electric brakes, so will stay with them, but will definetely go for both axles.

I have found electric brakes to be excellent. Decent on steep hills, the trailer coming round to visit the front of the car on long muddy roads and the ability to set them to the load.

Someone mentioned a 'pig' trailer or to attach the steering front end off a light truck. This would solve the long spring and drawbar issue... We'll see.

Cheers

Geoff

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#3

Re: Suspension for an offroad Tandem Trailer

12/14/2010 11:06 PM

pictures?

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Location: Australia, down south, Melbourne, then slightly west to, Geelong
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#4
In reply to #3

Re: Suspension for an offroad Tandem Trailer

12/15/2010 5:01 AM

G'day Chris,

Youcan see the current suspension is a little over loaded and the shock absorbers are on quite an angle. I was going to put an extra leaf in, but with the extension am re-thinking the lot. I get the additional box section this weekend, so will lay it all out with the frame and take a photo of the spread of the load. I am keeping the frame light with 50x50x3mm box section, as per pic.

Cheers Geoff

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