Thread: 4WD box trailer 1.4t dwgs attached.

Looks quite good and simple. There is scope for weight reduction if you want to go that way. Regarding the ball height. I've always used 450mm as design height. There may also be requirements that the coupling can't hit the ground first.

Good job.

I've built a few trailers, one thing I notice is all the joins in panel work, with my trailers i get the floors folded so the sides are part of them these tubs drop into/onto the chassis, on commercial trailers they are prone to rust there (under the floors/sides), and that eliminates this design flaw. Make sure that every over-lap of sheet to RHS (assuming you don't get it galvanised) is thoroughly drip checked.

Slipper springs - I'm not a fan of slippers, use shackles, especially if you are making it with a 1.4t capacity. In fact, I'd go as far as using automotive leaf springs instead of the high arched trailer ones, otherwise my personal preference would be independent.

Drawbar length is good, as is the RHS sizing IMO, should tow well. Also expect to exceed that goal weight slightly...

Cheers
Will

As you have stated it's a 4WD trailer to be used off-road. my suggestion would be to mount the springs above the axle and use solid mount point at front and shackle plates at rear for better stability.
Also make the drawbar as short as possible, bit harder to back, but it will follow your car better and do less damage to your trailer and Eco-Drains off road.
I like to have the length of drawbar that allows me to jackknife the trailer without the rear corner of your 4WD hitting the front corner of your trailer, you should be able to jackknife right up to your drawbar without doing any damage.
On an Army trailer with the single pole drawbar you can jackknife right up to 90 degrees, plenty of room to jackknife will get you out of some sticky spots off-road, good luck, Regards Frank.

The Australian Design Rules (ADR) state the centre line of the ball from ground level should be between 350mm and 420mm when the vehicle is laden.


This is a bit hazy I reckon, as is a bit hard to know where the ball height can be if unladen.


Yes, I take your point about shedding a little weight - in the end though it will be a little on the heavy side. Its mostly for carting wood - so needs to be tough.


Will explore the coupling hitting the ground rules too - thanks.

Tank, Thanks for your input. Yes I did talk about a 4WD Trailer. Buy this I mean it sits behind a 4WD, with 4WD wheels and tyres, so it all sits and rides at the same height. Its really a general use tough trailer for heavy loads without going to dual axle.

Originally Posted by browndogrider1

The Australian Design Rules (ADR) state the centre line of the ball from ground level should be between 350mm and 420mm when the vehicle is laden.


This is a bit hazy I reckon, as is a bit hard to know where the ball height can be if unladen.


Yes, I take your point about shedding a little weight - in the end though it will be a little on the heavy side. Its mostly for carting wood - so needs to be tough.


Will explore the coupling hitting the ground rules too - thanks.

So just having another look with regards to weight and strength.
On the drawbar I'd remove that centre spar and also the mitred short sections where the drawbar beams meet the sides. None of those are helping with strength, only adding weight and complexity. You can move the cross-bar between the drawbar beams back to pickup the spare wheel mount.

Take a look at your axle strength vs deck strength. You're using 75x50x3 RHS for the deck frame with 50x50x3 in-fills, where the axle between the wheels is 45mm and takes more load with a longer span.
I'd look at using a heavier axle and/or far lighter deck framing to get those much more equivalent. Otherwise you'll bend/break the axle 3x before you hurt the deck.

I'd consider using duratorque style suspension or even air springs with oil dampers. Springing a trailer for the load makes them travel and tow a whole lot better. My experience with leaf-spring trailers is generally awful, they only ride well with max weight in a narrow speed range and they almost never carry max weight.

Yep - might remove the centre spar. Though this trailer will be fully loaded from time to time - more weight than a camper trailer. Most camper trailers a centre spar, and their ATM is perhaps 1/3 less weight.


But am taking out the 50x50x3 centre infills that runs between to floor cross members.


The axle is actually 1.5t rated, the ford bearings are rated at 1.4t, and the springs rated at 1.5 t. So the weak point would be the bearings if anything.


The floor member are actually 50 x 75 x 2.5mm (not 3mm).


It terms of suspension, this is a general heavy duty trailer for general use.


The best design is an eye to eye, or slipper spring, as their is minimal travel with a 70mm wide and 7 leaf spring. The trailer with 1 tonne of sand should drop the trailer only 60mm approximately. This is what you want with a general use trailer. This trailer is heavy enough unladen so it won't bounce, and yet when loaded will sit level and feel stable.


That's the idea anyway.

My 'off the shelf' box trailer (6x4) has done a lot of heavy duty work, like you, mainly firewood and on tracks that others would not travel on.
The secret was light springing, and reducing tyre pressures when trailer is empty.
I got the heavy duty suspension replaced with light duty springs when I got it. Because the wheels have travel, less impact on the bearings. It is possible for the axle to hit the bump stops, but I do not think they ever have.