[jono165]

I'm about to start building a single axle 2000kg rated car trailer to put my suzuki on. It'll be a flat deck style trailer with the deck dropped and drive over guards.

Is there a way that I can calculate the deflection of it with a load on it? I'm thinking of using 100x50x3 for the chassis/drawbar with 50x50x3.0 cross members.

There's a lot of terribly made trailers out there so I want to make sure mine is strong and safe. I am trying to avoid a 'truss' down the sides of the trailer, while this adds strength it means I can pickup pallets etc with it.

Am I over thinking this or do I just copy someone else's design?

Also what do people think of a maximum deck height for a car trailer? The tyres I'll be using match my tow car are 29". Alot of box trailers seem to have the deck at about 500mm and I think I'll end up more like 600mm

[jono165]

Here's a rough idea of what I'm looking at.

I'm estimating the trailer will be around 550kg and my suzuki is 1280kg loaded

[jdk81]

You might be overthinking it, but there's a lot of professionally made trailers which are junk.
It just depends how versatile you want it.

You can truss beneath the outside rails with some pipe, a bit like truck trays.
It would add a heap of strength and it would be helpful when tieing down.

Thinner sheet in the floor, and more cross members which are trussed with some rod etc is the most weight efficient.
Alternatively aluminium ute trays are an awesome source for strong lightweight flooring options.

Which axle and bearings etc will you use?

[30ONA]

I don't know if anyone is doing it yet or if legal to register. But there are people making bridges out of fibre reinforced plastics. Super light and strong, these materials could be investigated for trailers. I'll ask one of our suppliers if they are doing it already. The bridges I'm using from them will take a 6t ambulance on a 16m span.

[jono165]

My axle is a 2200kg axle from a Renault master van, the van itself was rated to something like a 1680kg payload. I'm doing this because my tow car is a 2008 VW Touareg, the stud pattern is 5/130 which is the same as a renault master.

It has steel parabolic springs that go with it and hydraulic calipers for hydraulic over ride brakes. The bore of the caliper is pretty much the same as a trailer one so a normal trailer master cylinder will work fine. The mounts are also super simple to work with.

The bearings are massive 80mm diameter, 48mm wide and I'll get a spare hub to mount the spare tyre on as its not something that common.

For those interested I paid $65 total for the axle, brakes, leaf springs and mounts. I've got 3x Audi Q7 wheels which I picked up for $15 to go with it.

Floor i Was going to use 2.1 or 2.3mm chequer plate, possibly in aluminium depending on price and support it under where I'll drive. Theres 2x 100x50x3 rails under the 'tray' part of the trailer which the suspension mounts to the side of, these are 1092mm apart, so with the car centred over the trailer theres 150mm of depth between the bottom of that rail and the deck.

Fixed hanger


Shackle Hanger


Spring


Hub/Axle

[just_cruizin]

What dimensions will it be?

Suspension width sounds really narrow and this will be unstable. You want the suspension as Wide as possible

What's the weight of that axle.

If you intend using it for other purposes consider using flat sheet rather than chequer.

[jono165]

dimensions of deck are about 3600 long x 2100 wide.

The distance across the outside of the tyres is is 2010mm. I can't really have a trailer as wide as a typical car trailer with the guards outside the deck as it won't fit down my driveway.

Edit: The weight of the axle/brakes/hubs and springs is 100kg combined

[just_cruizin]

you'll have almost 500mm outside the springs on each side, that is huge.
My dual axle rocker suspension setup was about 120kg total. Just because something is cheap doesn't make it the ideal solution.

Also try and drop some height out, it will help with stability and reduce wind drag. I got my trailer down to about 400mm, but that is very low. Mine is about the same length as yours but with the dual axles a lot less overhang.

[jono165]

It's more like 400mm either side of the springs. As the mounts sit outside the chassis not inline like typical trailer springs.

I was working out the heights and yes I'll have to drop the deck to keep the deck as low as practicable. I am somewhat limited by my driveway and what fits down it.

I get that this isn't as practical as a trailer axle. But I can't see the spring spacing being much different really if I ordered a proper trailer axle to keep it all at the width I need. Or I could move the spring pads on the axle outboard as far as possible.

And there's no way to have the same stud pattern wheels on a trailer axle unless I got cutsom hubs made up. My tow car only has a space saver spare so it'd be nice if all the wheels matched when towing.

[just_cruizin]

Normally you can get hubs drilled to suit any PCD

[30ONA]

[quote="jono165"
Is there a way that I can calculate the deflection of it with a load on it? I'm thinking of using 100x50x3 for the chassis/drawbar with 50x50x3.0 cross members.
[/quote]
There sure are. Here are the basic ones for a single member. http://www.engineersedge.com/beam_calc_menu.shtml

[striker99]

I feel like with all that weight a dual axle trailer would be more appropriate...

[just_cruizin]

A single axle is fine for a sierra, single axles are a lot more nimble however this does limit the use of the trailer considerably

[30ONA]

What about a dolly. Keeps weight and size down. But you could make it flat with just two small holes for the tow trailers. Then it would still take a pallet. I don't think you axle Will work though, you'd need a wide one.

[jono165]

I'm not interested in a tow dolly. I'll spend some time in the shed this weekend and work out what I can get the deck height down to. That's my limiting actor with stability. It'll pretty much be a purpose built trailer so a single axle is fine I found a calculator that lets me play with the load positions on the trailer to determine the axle position to keep my ball weight around 10%.

[got_bar_work]

Try monopan for the deck

[just_cruizin]

Check with the trailer design guidelines in your state or ADRs as this also determines axle location

[Eddy]

Having wheels to match your tow vehicle may seem like a noble thought, but in 40 + years towing, I have never found the need to make use of this "convenience" and I've towed to some fairly gnarly places.
I firmly believe, backed up by experience, that your way better off sticking to standard trailer components .... which leads me to your choice of axle. The likelihood of finding anyone to sign off on that for rego is extremely remote. You'd be far better of getting a rated trailer axle from a reputable supplier.
Another thing I have learned, is that single axle tray top trailers are an absolute pig to load and to tow.
If you feel that you must have a tray-top for both your car, and other loads, you are way better off, by a huge margin; with a dual axle setup, and using smaller wheel / tyre combination.

[jdk81]

I think VIC roads will sign off on it pretty easily, as long as you have functioning brakes, correct lights, ticking all the boxes etc and the appropriate safety factor.

It wont be much worse than rocker roller suspension to load, it'll require careful positioning of the sierra for correct down ball weight.
You may require bumps/stands or something on the rear of the trailer to use when loading, to stop it from pulling the tow ball excessively.

Get it as low as you can.
You could have some removable plates, that you can remove so you can have lower sections for the sierra wheels to go, which would also assist with proper wheel position, making loading the sierra in the correct position easy.
When you want a flat top, install the plates.

What is the eye to eye dimension of the hangers for the springs?
What is the wheel track of you sierra?
How long will your drawbar be?

Chassis needs safety factor of 3 for highway, and 5 for offroad.

https://infrastructure.gov.au/roads/veh ... spx#anc_19

Vic roads trailers
https://www.vicroads.vic.gov.au/registr ... or-caravan

VSN1 for trailers
https://infrastructure.gov.au/roads/veh ... etin/vsb1/

[jono165]

jdk81 wrote:

Get it as low as you can.
You could have some removable plates, that you can remove so you can have lower sections for the sierra wheels to go, which would also assist with proper wheel position, making loading the sierra in the correct position easy.
When you want a flat top, install the plates.

What is the eye to eye dimension of the hangers for the springs?Off the top of my head springs are around 1400mm eye to eye, theyre quite long.
What is the wheel track of you sierra?My sierra is 1620 to the outside of the tyres which makes the track about 1365 as a run a 255 tyre. I will need to drive over the guards of the trailer
How long will your drawbar be? i was thinking a 1200 or 1500 drawbar

The vicroads part is very straightforward. The measure the trailer and check the lights and make sure it has some form of brakes for a 2000kg trailer. That's it.

The single axle is fine, as long as i get the axle in the right spot. I'm looking at about 1800kg total load with the car on it, maybe a touch less.

JDK, I did think of that about having the lowered sections but I have more of a think about what I'd use it for other than a sierra and I think a big box trailer might be a better option. It puts way more strength into the trailer, and I can have the wheels come up as much into the tub as I need to keep it low. If i really need to load a pallet it can go in the back and be pushed forward a bit so get it loaded nicely.

I'm also thinking I'll make it only 10' or 3000mm long. I cant see myself having anything with a longer wheelbase and if I was to get another project it would be a SWB LJ to club reg

[jono165]

Stolen from Josh's build thread but I think this is the better way to go but with the single axle and a bit narrower with the wheel tubs in the trailer. I need the narrowness to fit down my drive.

[30ONA]

Flat tow! Buy a box trailer for pallets. Your going to compromise on one or both trying to get one trailer to do two jobs.

[jono165]

I'm pretty sure the tow vehicle has to be so many times more than the gvm of the vehicle being flat towed. That's not an option for me.

[Eddy]

jono165 wrote:

I think this is the better way to go but with the single axle

yep ... now ya talkin"!

... was getting all nervy and twitchy at the thought of that tray top thing ...

[Red89]

My deck is 725mm off the ground, my deck is 2420mm wide and the tyre face is 610mm out from the spring hangers. It tows great, sits higher then I would like but I picked it up licensed for $1000 so cant complain.

[fordem]

jono165 wrote:

I'm pretty sure the tow vehicle has to be so many times more than the gvm of the vehicle being flat towed. That's not an option for me.

Whilst I have no knowledge of Australian regulations, I would expect there to be a similar requirement for a vehicle on a trailer, and I would be quite surprised to learn that a tow vehicle meeting requirements to tow a vehicle on a trailer did not also meet requirements to flat tow the same vehicle.

It's all about the ability of the tow vehicle to control the weight that it is towing, and when the vehicle being towed is on a trailer, the weight of the trailer has to be taken into consideration, if flat towed, the weight to be controlled is less.

[30ONA]

fordem wrote:

jono165 wrote:

I'm pretty sure the tow vehicle has to be so many times more than the gvm of the vehicle being flat towed. That's not an option for me.

Whilst I have no knowledge of Australian regulations, I would expect there to be a similar requirement for a vehicle on a trailer, and I would be quite surprised to learn that a tow vehicle meeting requirements to tow a vehicle on a trailer did not also meet requirements to flat tow the same vehicle.

It's all about the ability of the tow vehicle to control the weight that it is towing, and when the vehicle being towed is on a trailer, the weight of the trailer has to be taken into consideration, if flat towed, the weight to be controlled is less.

Yes you are correct, but it seems so is Jono.

This from a vic roads document. file:///C:/Users/100591/Downloads/vsi6requirementsaframetowing.pdf

The following requirements apply to the towing, with an
A-Frame, of an unbraked motor vehicle where the tare
mass of the towing vehicle exceeds 3.5 times the laden
mass of the towed vehicle.
Persons wishing to tow with a vehicle that has a tare
mass that is less than 3.5 times the laden mass of the
towed vehicle are required to have control of the brakes
on the towed vehicle. Such persons must seek further
advice from VicRoads or from a Vehicle Assessment
Signatory Scheme (VASS) Signatory

[jono165]

I was going to write something similar but 30ONA beat me to it.

It all gets a bit hard with an A-Frame with the braking. My understanding is even if 'hitch n go' has a braked version of the A frame I'd still need an engineers cert.

Also with a trailer it doesnt matter how much I break my car I can still tow it home.

A 2000kg big box trailer is the most handy for something small like a suzuki, and can do tip runs, move the odd bit of furniture and take stuff that wont fit in my tow car. I'll draw something up in sketchup over the next day or so and post it on here.

[Eddy]

Just don't go too far outside the proverbial "box"
Keep it simple and "normal" for the plain and simple reason that situations and lives change, and sooner or later you will want / need to sell it. Way easier to sell something for a good price if it usable to a wide variety of potential buyers.
the standard Box trailer with wheels outside the tub can be sold almost by word of mouth. Wheel arch inside the tub not so much. Lighter weight tray-top near impossible.

For many years I towed a LJ50 on either a 8x5 dual axle box trailer, and earlier (before I replaced the stock bar treads with 31x10.5 tyres) I towed it on a converted boat trailer. The dual axle trailer was great, as I could load with or without being hitched to a tow vehicle, and even without ramps.

[fordem]

30ONA wrote:

Yes you are correct, but it seems so is Jono.

What is the requirement for a trailer?