Considering a camper trailer

Relatively precise measurements are also important.

I just measured the draw bar on my 7x4. It is 1670 mm on each side - i. e. 3340 in total of 75x50x3, therefore only 83.5% of the weight you have allowed in your guesstimate. It all makes a difference.

Tub floor size should be 1220x1830, 500 sides with a 50 mm rolled top and 25 mm downward vertical rolled/bent edge - 2370 mm total from side to side.

Like the 40x40 axle, having 500 mm sides will add a small amount of weight, but almost everything is built to a 500 mm module size these days. Having 300 mm sides is quite restrictive. That's what I have. My car fridge is 445 mm high. It won't fit in the trailer or cargo area of my car ... :(.
 
I should refer to it as a 1800x1200.

I want a 1300mm drawbar length and I want it to tie in to the front spring hanger set 700mm back.

Could you double check your drawbar thickness is 3mm?
 
My drawbar is welded on to the perimeter frame 405 mm back from the front of the tub frame. The front spring hanger is 515 mm from the same point. The 1670 mm is measured from the very front of the A bar to the end in front of the spring hanger.

On the centre line, the welded ends of the 75x30 are (approx.) 1100 mm from the front edge of the perimeter frame. There is probably a little parallax error in that last measurement. This does not include the protrusion of the hitch, which is around another 250 mm to the very front of it (i.e. not to the pin centre).

Drawbar is definitely 75x50x3 mm.
 
The perimeter frame on mine may well be 50x50x2 mm. Several reasons:

1) The original drawbar was this size; and

2) It goes "TANG" when struck with the end of an Engineer's Rule, rather than "TUNG" when I use the same thing on the 50x25 mm forming the new part of the ladder frame, and also the side of the new drawbar, both of which I know to be 3 mm thick; and

3) It is square edged, not round edged like structural box.

Regardless, it has now lasted 30+ years without any sign of distress or damage. It is welded shut at all points, so the thickness cannot be easily determined by direct measurement.
 
Thanks RB, If 2mm framework has held up for 30 years on your trailer I am happy to use it on mine.

Are you happy with that pivot to axle length?
 
Gidday ST

Two things need to be stressed:

1) the original 25x25 x1 ladder framing had to be completely replaced at the 12-15 year mark, as the top part next to the floor of the tub had completely rotted away (not sure if this was 1 or 1.6 mm thick). Bloody amazing that the trailer didn't disintegrate at 100 + kmh on the Cape Otway road one night! It was replaced with 50x25x3 and the tub floor was replaced with a 'bucket' of 16 gauge galvanised that comes half way up the previous tub walls. Neither of these is showing any signs of deterioration after 10+ years.

2) my trailer is 7x4. The axle placement will be different for a 6x4. Probably about 100 mm closer to the front of the tub, all other things being the same, but with higher sides. Accepted wisdom is that the axle should be placed behind the centre of the tub. Confusion reigns as to how much ... For a 6x4, I would be inclined to have it no more than about 100 mms to the rear.

There are quite a few other basic design parameters that need to be considered. I eventually got most of these "right"! Some that I still haven't is to have the gas bottle/s on the drawbar, rear gate swinging sideways with the spare mounted on it. The placement of the internal gas struts is not ideal, and neither is the 300 mm tub depth. The latter cannot be changed without drastic alterations to the tent and annex - it would possibly be cheaper to sell and re-buy if I were to do the latter! That's NOT going to happen!

You are very sensible to keep everything light and minimalistic. That is, keep it as a trailer for making camping more comfortable, not a camper trailer that's a replacement home, with 26" TV, en suite shower and toilet, etc ...

I very nearly ordered an Oztrail 7x4 tent for my trailer until I realised that it was completely impossible for me to erect it by myself (too heavy and too awkward), and the extra drop required me to extend the trailer sides and gates upwards by 200 mm. I can furl and unfurl the Oztrail Camper 6 easily by myself, including all parts of its very commodious annexes.

As I mentioned previously, getting the design right on paper is the hardest part. Having a very clear idea of the finished item is central to that. Write it all down!

The tub floor should be slightly wider than 1200 wide so that one can slide sheets into the tub when one needs to use the trailer for the other exigencies of life. These sheets are often 1220 mm wide ...

I should also mention that the perimeter frame on mine at front and rear extends out to about the width of the mudguards. The sides of the tub are then braced to these extensions all round. The ends are blanked off, being fully welded all round, as are the side rails that terminate on the front and rear chassis members. The blanking piece appears to be heavy bar or plate, around 4-6 mm. This makes this part of the structure very strong and rigid. The fillet piece is light plate steel, and is good to this day. The side tie down/reinforcing bars are welded to these and the mudguards. The angle iron sides added to the new pre-made gates also fix to these fillets. i. e. They are integral to attaining overall rigidity and strength of the entire unit.
 
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Good point re: tub width, I am probably best determining ideal (read Subaru) track width and working backwards from there with clearance to tyres.

I have printed 1cm graph paper and I'm on the 3rd design already.

I was working with a 10℅ of load space axle backspace, I will revise this.

The tent will be set at the front of the trailer leaving 400mm of tub with headroom at the rear. The weight being offset somewhat by a 59L water tank underslung behind the axle.

75mm tops on the sides seem about ideal to sit a beer on.

Braces from the front edge to the guards will deflect objects or the trailer if I forget the trailer is there and hit them - not sure if I want to use steel sheet or bar, both have advantages.

I'm thinking 75x50x2 for the drawbars and 50x25x2 for the frame.
The floor and sides bent out of 1 sheet of 1.6 would be best but I'm trying to think of something lighter. The tent support uprights will add strength to the sides. I agree 500mm for the sides is a must! If the tent can seal 80% of the trailer when lowered I will only have to find a solution to cover the last 400mm, if not a full tonnau cover will keep **** out.

Front and rear tailgates will give utility for long load carrying - the front will fold down to sit on the drawbar but I'm tossing up whether the rear should drop or swing.

Springs will be the longest 3 leaf eye to eye I can find. The axle slung underneath. I still haven't ruled out adding dampers.
 
^ All to the good ... :biggrin:.

I wasn't very clear about the axle placement.

The tub on mine is 1030 mm from front of tub to axle centre and 1080 mm axle centre to rear of tub (approx. There will be some parallax error there).

My trailer axle is the wrong way around! the axle should be about 1080 from the front of the tub and 1030 mm from the rear - i.e. very slightly biased towards the rear of the tub.

Not that this has ever been any kind of problem. Not prior to either of the two rebuilds (minor and very major); nor after either of them.

The overall width of my trailer and its track are all but identical to those of my Forester. It is maybe 1690 mm overall width (car = 1736), and the track is all but identical at 1675 vs 1695/1685 (F:Rcar). This measurement is taken from the O/S of the tyre sidewall not the centre line of the tyre (1495/1485 F:R - car). A counsel of perfection is to get the track identical - but to which measurement?

Having the trailer slightly narrower overall than the car gives sufficient "wriggle room" when doing traffic manoeuvres, and doesn't hurt when off road either.

You also need to think about how to seal the top of the trailer where the RTT joins to it. It seems that you will have the same problem as I had if your RTT is 400 mm shorter than your trailer ... Is your RTT base board really only 1400 mm long?
If so, maybe best to shorten the trailer to suit its length?

I find my current tow bar length to be good. It doesn't have any tendency to dig in even on quite sharp changes in vertical direction. Since the drawbar A frame steel is open ended at both ends, if it were to dig in, it would be unlikely to damage either the car or trailer. Part of that equation is the height of the tow tongue. Mine is approx. 435 mm to the top of the tongue (not to the top of the ball/pin).

If I were you, I would use 75x50x3 for the A frame side bars. While mine was originally 50x50x2, it was reinforced along both lengths with heavy 50x50 structural angle iron for most of its life. The very small saving in weight is more than offset by a very considerable reduction in strength. As Jimi said to me, the drawbar is the one part of a trailer that you really do not want to damage or break. It is difficult or impossible to repair in the field. That's good advice IMO.
 
I might compromise at 2.5mm.

Tent is indeed 1400, queensize bed with 150mm extra at the end so fitted sheets don't - fit.

I think the Extra 400mm of trailer will be more of an asset than a liability.
 
A queen bed mattress is 2000x1500 ...

Perhaps you have a "short version" ... :poke: :raspberry: :rotfl:.

Or maybe you need to re-measure it?
The old adage that goes "measure twice, cut once" ... :lol:.
 
Double = 1140 x 1930 ...

What are the dimensions of the base board of your roof top tent?
 
Rb my base folded is 1200x1400, 2400x 1400 d eployed .

bb the tare of those trailers almost exceeds my gvm
 
Interesting site, ST, but I have serious problems with some of the design for a single axle trailer. I reckon that my 30+ y.o. trailer was better designed when built! All sorts of little things ...

Probably the most useful part is the parts/components list. Not the item specifications, but the list itself ... :poke:

I have converted this list into a PDF image, then into an Excel spread sheet, if anyone's interested ... :iconwink: :biggrin:.

I agree about the tube axle. The main problem is properly securing the stubs into it so that they cannot flog themselves to death. Possibly with a 1/4: wide cut through the top and bottom of the tube near the end of the stub (maybe 1" outwards towards the rim?), then weld the inside end of the stub via this cut.

IMO, much easier and stronger just to have a standard axle made to length out of proper bar, by a proper axle fabricating workshop.
 
Ratbag said:
Interesting site, ST, but I have serious problems with some of the design for a single axle trailer. I reckon that my 30+ y.o. trailer was better designed when built! All sorts of little things ...
Click to expand...

And it's all of those little things I want to know now in the planning stage...
 
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