Newbie Trailer Design Help

[Strop]

Hi gang,

I am in the process of getting someone to build my trailer for me. They build their frames out of 75mmx50mmx3mm SHS with the cross beams being 50mmx25mmx2mm SHS. Asked about C channel and they only have it in big pieces and he said the 3mm angle would weigh almost as much as the stuff. Only the bloke that builds trailers in town booked out till April. My estimate is that the trailer frame should with 83-85 kg without any axle or wheels. My design is below.

Screen Shot 2014-10-29 at 3.46.17 pm.png (74.08 KiB) Viewed 1159 times

As you can see I am planning on the spare tyre being under the back and a 45 litre water tank just under the axle line .

Now for the hard part. I understand nothing about axles and the distances required for clearance etc. I know my problem is the water tank. I don't want the axle coming up and hitting the tank so I think that rules springs out, unless the axle is hung under the spring instead of on top. It is not a 4WD unit so I want it to be sleeeeeek. So I think that rules springs out.

Therefore I believe I need a torsion axle but I am not sure if there is enough clearance for one of those even. What I did find was Flexiride half-axles, but I am not sure about them either. I am hoping to bring the build in around 400 Kg but still doing some maths there. Intending to cover it in fibreglass sheeting that doesn't weigh as mush as aluminium.

Here is a link to their specs sheet

http://www.alltrailerspares.com.au/Asse ... 0specs.pdf

Screen Shot 2014-10-29 at 3.51.34 pm.png (35.27 KiB) Viewed 1159 times

So to fit it all in I need a breather hose connection on top of the tank (30mm) the tank itself (105mm) and finally the straps holding the tank up (5mm), giving me a grand total of 140mm. That means it hangs 65mm below the side frame.

You can see on the diagram I have marked the 60%, 62.5% and 65% of the body length marks across the trailer. The centre of the water tank is about 61.75%.

What advice do you have for me. Thanks

Laurie

[dales133]

Hi Laurie , I'm in geelong where do you hail from?
I'm doing the same thing as you pretty much with help from a friend we are building it at my place, the trailer that is.
I'm no expert when it comes to axel placement and more qualified people can help with that but I'm building mine on springs and it is a 4x4 build with a much bigger water tank 90L and I waited until I'd worked out the axle placement then mounted it just behind it.
I can't remember the exact calculation I used for axle but I went for the "optimum calculations as opposed tho the slightly forward or aft options... mostly based on water tank consideration

[Strop]

Dale,

From Armidale, NSW. My build not quite as BIG as yours. Mine trailer will be on the road or good dirt only.

I had almost given away an under frame tank then stumbled across a couple made out of plastic. Only 45 litres but most places I intend to go won't have water and camping only for 2-3 days so important to have it. I was looking at 20 litres in the galley but this gives me back that space. Not cheap like some others but hopefully it will work. I could get a bigger one but a LOT more $$$$$ and I couldn't mount the tyre under the back.

I wish I had a mate who could weld - well I have a few but not sure how square it would be at the end so better to pay for it.

I just hope this might work. Still seeking that advice that it should or not?

Al the best

Laurie

[dales133]

My water tank was about 220 and holds 90l but I originally purchased the tank I assume yo had.
But the plastic tanks were 80 bucks for the 45 and 120 or so for the 90 and over 100 more for the skid plate and Brackets.
Check out the huntsman ones.

The 90l tank is about 900 X 450 X 180.
Great low profile tank. With brackets

[Strop]

I have seen the black plastic huntsman ones. They have a depth of 170mm. I have also seen similar ones at 180mm. That will add 70-75mm to the depth. If I can get away with it using this design I will jump at it. Tank is less than half the price and you can carry twice the water.

There is the option of putting the tank hard up against the floor and losing the breather on the top having to punch a hole near the top edge. Would lose a bit of water but might work.

Still don't want the trailer to ride too high.

I have read things about these Flexiride axles but I am having trouble understanding how they work and effect ride height.

Laurie

[KCStudly]

You will find that the makers of the individual axle stubs also recommend a xmbr to reinforce the mounting pad locations and prevent frame twist, so the Timbren style does not solve your tank mounting situation.

If you are going to build a sandwich panel for the floor, you might be able to gain an inch by creating a pocket or bump up in the underside of the floor; leave out the bottom skin and insulation at the tank; maybe even have an access panel under the mattress to allow servicing the vent and fill connections.

Another option would be a custom tank that drops down in front of and behind the axle; just need a crossover tube or dual pickups/foot valves to be sure that you can empty both sumps (?)

[dales133]

The huntsman one I was referring too was the stainless steel o e that comes with breather, 2 outlets and a 1 1/2 FILLER.
As kc said you could recess it into the floor.
Stainless dosn't need all the extra protection that costs more and your water dosn't taste like crap. You can view it on ebay

[Strop]

The half axles look like they bolt onto a plate. If the plate was welded to the frame and to another piece of metal going between the two cross members would that stop twisting. You could even use the same size steel as the side frame for the cross members near the tank.

I have thought about the air vent coming up into the floor space. As I intend to have some under bed storage that should be possible but I will have to check to see where that will come up.

Laurie

[KCStudly]

...another piece of metal going between the two cross members would that stop twisting(?)

IMO, the extra cost of the individual axle halves provides only a small advantage of ground clearance, since compared to a full torsion axle the xmbr can be mounted flush with the frame. If you are not planning for rough conditions that isn't really a factor for you. So assuming you go with a full torsion axle, maybe the thing to do would be to mount the tank just ahead of the axle. Keeping the tank close to the axle would still help minimize the effect of variable ballast, but would solve your packaging issues.

[Strop]

This is a quick picture of what I was trying to describe

Screen Shot 2014-10-29 at 11.20.17 pm.png (15.13 KiB) Viewed 1116 times

You would then bolt the half axle to the plate

[Strop]

KC,

If I move the tank forward I can use a sprung axle I don't need the torsion one. Cheaper too, but I lose that balance. As shown the water will have almost no impact on balance of the trailer as it is positioned straight over the axle.

The question is if I go that route of putting the tank right at the back and the spare tyre further forward how will it impact on balance and tongue weight. Or do I ditch the spare all together? Just carry a can of goo around to pump into the tyres in case of a flat.

Dale, the tank is good value - just wonder how much freight is......

Laurie

[KCStudly]

Carrying a spare is a better idea because it can cover a lot more scenarios than just a minor puncture (blow out, lost tread, busted belt/bulging, heavy gouge, lost valve stem, etc.)

Thanks for the picture, that makes it much more clear what you are proposing, and IMO is a great solution, other than the extra weight and cost of the axle units.

I guess it comes down to your design goals. 45 liters is about 12 gallons which will weigh about 100 lbs. Shifting 100 lbs forward by half the distance of the width of your proposed tank (so that it sits just ahead of the axle) will shift about 11.6 lbs onto your tongue; maybe 1/ct of your final over the road weight. Put one CI DO in your galley and it cancels that out. Drink all the water and you are back to square one.

But if your TV is very sensitive to hitch weight, and you really want the tank dead on the axle, what you have drawn there looks good to me.

[KCStudly]

Thinking about it some more, and maybe something you hinted at, with the torsion axle the cross piece actually is further forward than the center of the axle hubs, so the tank would have to be shifted further forward, or the tank and tire locations could be swapped with the tank nestled closer to, but behind the actual spindle pivot point. Putting the tire in front of the axle might actually balance out the offset of the tank. ... but it would make it a little more difficult to get to the spare if needed(?).

Just spewing my pennies in your general direction 2 cents at a time.

[dales133]

Tanks freight is 15 bucks I think if you purchase through eBay.
I'd ditch the spare underneath idea and put your water tank at the back and go for a sprung axle and use what you save on the stainless tank.
I've made no provision for a spare yet but I'm going to have most of my weight on or behind the axle so I might just chuck it on the drawbar

[Strop]

The problem with a big tank at the back is the tongue weight or I should say more correctly the change in tongue weight. Full it is at about 80Kg and if empty that shifts a lot of weight back to the front. It is ok if you have a big 4WD but I am going to tow it with a car that has a pretty high tounge weight ability, as does my sons but, my daughters car doesn't and it will be available for family usage. The beauty of the tank over the axle is that it should not impact very much on tongue weight dry, full or half full.

I am doing a spreadsheet today to try and determine as close as possible the final weight of the unit. Based on that I will know, if I read the specification sheet correctly, which of the half axles I need. The more weight the longer they are. I might even be able to fit the stainless tank in if the weight is low enough. It will drop down 45mm more than the plastic tank as I can put it hard up against the floor with the breather being on the side not on the top.

I just have to figure out where the axles get fixed to and how much clearance I need. Having trouble getting my head around it.