Thread: Alloy tray trailer / caravan chassis

Gday all,

I am about to start work on converting a large caravan chassis into a tray trailer. I will post pics as I go along.

But firstly, a few questions if I may. The chassis right now is stripped ready to go. Main frame and drawbar is 127mm x 51mm(??) and looks to be about 3mm so is well made and strong enough. I have already replaced the axles, wheels, coupling and has mechanical drums on the front axle so should be right for a 2 tonne rating. It also has roller rocker suspension.

I have purchased a large alloy truck tray that is about 4.5m x 2.5m as it was so cheap and could not go past it. Rails on this look to be about 800/900 wide. (Just waiting on the exact measurements). Chassis width on the trailer is 1700mm centred on the side rails. So looking at those measurements, this would mean that they current tray rails would be sitting in about 400mm from the current side rails.

If I was to weld in cross members (4 or 5 of them) in between the side rails that are the same size (127 x 51), and then mount the tray to these, would this be strong enough to take the load on the tray.

I also have a large truck box that is 1mtr square (on the end with a door in each end) and 1.8m long that I was going to mount on the frame in front of the tray. This would weigh about 125kg. I have read about placement of the axle being 1/2inch to the rear for every foot of length. Can I incorporate the box into this measurement too or should I just use the length of the tray for the axle placement. I am a bit concerned about drawbar weight with the box.

I hope this makes sense.

Krico

I built one of those some years back. 14' x 7' tray 8' across teh wheels. We split the tray and infilled the area between the wheels with timber to get the lowest tray height.

I've had numerous people knock on my door trying to buy it over the years. I may sell it this year if the money is right. Weighs a tonne but towes well, much better than it did as a van. I'd trow 2 tonne on mine as is. YMMV.

Hi Krico, and Welcome.
The thing to be mindful of with using a Caravan chassis as a flat top tray trailer, is that most older caravans designed their chassis to have the walls of the caravan as part of their structural integrity. So once you remove the body, the chassis will be quite flexible, ie; not ideally suited for large loads either end of a long trailer without additional support. But it sounds like your chassis will be able to cope
Your axle placement calculation is correct. If you're mounting the tray and the box on the chassis and the box was is going to be permanent, then yes, incorporate the box in this measurement. If the box was to be consistantly removable, then I'd suggest not.

Originally Posted by Yonnee

Hi Krico, and Welcome.
The thing to be mindful of with using a Caravan chassis as a flat top tray trailer, is that most older caravans designed their chassis to have the walls of the caravan as part of their structural integrity. So once you remove the body, the chassis will be quite flexible, ie; not ideally suited for large loads either end of a long trailer without additional support. But it sounds like your chassis will be able to cope
Your axle placement calculation is correct. If you're mounting the tray and the box on the chassis and the box was is going to be permanent, then yes, incorporate the box in this measurement. If the box was to be consistantly removable, then I'd suggest not.

Yonnee,

Thanks for the reply. I think with the size of the current rails and welding in cross members the same size or maybe 100 x 50, it should be a fairly rigid frame. Length wise it should be ok. I think I am going to have to lift the tray to get tyre clearance anyway so I may be able to incorporate a web like frame under the tray rails to stiffen it up length wise.

I am picking the tray up on the weekend but do you think welding in cross members will be enough for tray support or should i pack it further out on top of the chassis rails.

And is 70mm enough clearance for tyres with roller rocker suspension under the tray?

Thanks

Krico

Well I picked the tray up on the weekend. Not a bad deal for the $260 I paid for it.

tray1.jpg

Originally Posted by krico

Yonnee,

Thanks for the reply. I think with the size of the current rails and welding in cross members the same size or maybe 100 x 50, it should be a fairly rigid frame. Length wise it should be ok. I think I am going to have to lift the tray to get tyre clearance anyway so I may be able to incorporate a web like frame under the tray rails to stiffen it up length wise.

I am picking the tray up on the weekend but do you think welding in cross members will be enough for tray support or should i pack it further out on top of the chassis rails.

And is 70mm enough clearance for tyres with roller rocker suspension under the tray?

Thanks

Krico

You'd be surprised how only one diagonal brace can triangulate and strengthen the whole thing.

3" guard clearance would be the minimum I'd look at for rocker type suspension as there's a fair bit of movement in suspension travel without spring compression.