Thread: Initial Flat Top Trailer Planning.

Originally Posted by naddis01

Ok guys, I am after your expert opinions and guidance. I am planning on making a flat top trailer similar in basic design to Rod1949's but I have a few questions to get me heading in the right direction.

First off it will be a tandem flat top and I am thinking with a GTM of around 3500kg. At this stage I am thinking of a 12'x6' with removable headboards either end and drop sides.

Now the questions...
I said I am thinking of around 3500kg but is there a reason why I should go less than that? Like rego or bearing/axle capacities?
12'x6' is my initial thinking but then I thought maybe 12'x8' might be more stable for this sort of height and weight? Would that push up build costs too much, for example axle costs?
I have a current model PX Ranger so I was thinking of getting a set of secondhand alloys/tyres from a Ranger so they are interchangable. The Ranger has a GVM of 3200kg so maybe I should aim for that for the trailer?
As I said I was thinking a similar basic design to Rod's flat top trailer. What size material should I use for the drawbar, main chassis and the tray frame and floor?
How do I work out how much clearance I need between the tyres and the tray top? Ie how high would I need to make the uprights between the main chassis and tray frame?
What brakes should I use?

Anyway, it would be greatly appreciated if you could answer some of those questions to get my planning underway.


I am also considering doing a single cab Ranger tub trailer/camper if I can find a tub in a similar vein to my old Falcon one.

Hi, for the main frame I would go for 75X50X3mm RHS, draw bar 100X50X4mm RHS. Axles go for 45 round with Falcon bearings they are larger than std Holden, override hydraulic brakes on the front axle. Clearance would be what is between the axle and frame plus 30mm. Make sure the draw bar goes back far enough to connect to the front spring hanger. Regarding the springs are you going for a load sharing rocker, (highly recommended) as some states won't allow tandem slipper springs,
For the tray look around truck wrecking yards as the Ally tray will be lighter, allowing for more load capacity, 12X8 or 7'6" would be a good choice.
Kryn

Thanks for the reply. I would be looking at a rockers rather than slippers. I would prefer to build the whole thing myself so it is how I want it rather than making do with a secondhand tray.

Would 45mm axles be heavy enough?
What sort of tare weight would I be looking at using your suggested material sizes?
Looking at the RMS site, I assume that trailer rego works on the tare weight rather than the ATM or GTM?

I am now thinking that maybe the aim of 3500kg might be a little high. I just thought you could never have enough. What materials should I use if I was aiming for a tare of around 2T?

My trailer has an empty weight of 620 kg and is engineered to 2400kg total weight from memory.

It has Toyota rims 14" I think.

It is a 12' x 6' flat bed. Tows beautiful and have been using it for since 96. I swapped it for a car.

The drAw bar is about 6' beyond the tray.

If you would like photos I can post some tomorrow or Wednesday.


Dave

The Turning Cowboy

Originally Posted by naddis01

Thanks for the reply. I would be looking at a rockers rather than slippers. I would prefer to build the whole thing myself so it is how I want it rather than making do with a secondhand tray. Fair enough but a steel top would add extra to the tare weight.

Would 45mm axles be heavy enough? Certainly would do, if uncertain, ask where you are getting the springs etc from. The limiting factor is on the bearing end where it tapers down to the smaller bearing, Falcon are approx 7/8" Vs Holden 3/4", all the damaged ones I've seen, the most of the problem was in this area.

What sort of tare weight would I be looking at using your suggested material sizes? My rough estimate would be around the 800kg mark

Looking at the RMS site, I assume that trailer rego works on the tare weight rather than the ATM or GTM? You are correct on that

I am now thinking that maybe the aim of 3500kg might be a little high. I just thought you could never have enough. What materials should I use if I was aiming for a tare of around 2T?

I would still allow for a 3500kg as you never know when something comes up where that extra 1500kg may come in handy. Material cost won't be much different.
Regards
Kryn

Keep in mind that once you're over 2t gross you can't get away with override brakes - they've got to be independent and breakaway.

To go 3500kg you'd need 50mm square axles, a 'brake away' system and electric brakes on both axles. These is a bearing setup that you'll need as well, I'm not sure on the details on it but I'm sure someone can chime in with that or visit your local trailer spares supplier. And also make sure the springs, hitch and tyres are all rated accordingly.

Hi Naddis.
So much information to digest. Being from NSW, your first port of call is RMS because your Rego cost is based on the eventual Tare weight of the trailer you build, so this cost could have a bearing on what your eventual build will be. I personally think this is a dangerous way of rating and registering trailers as you'll get people building trailers from Balsa Wood to carry 4500Kg.

As for ATM or GTM, there are certain limitations which will impact your decisions as to what you build.
Firstly, a trailer's capacity can only be rated to highest capacity of its weakest component.
The highest capacity "Light Trailer" you can build is 4500Kg, and you can build a trailer to this if your budget allows.
Secondly, the highest capacity 50mm towball you'll find is rated at 3500Kg. This is also the same rating you'll get in an Electric brake coupling. So this is a fair rating to build a trailer of this size to. And you would always rate the trailer as high as you can. No point building a trailer that can safely carry 3500Kg, rate it and register it at 3000Kg, and get pulled over have it weigh 3400Kg.

The next step back is 2000Kg GTM. This is the point at which brakes are required on ALL wheels, and well as the ability for the brakes to apply themselves should the trailer become detached from the tow vehicle. By far the cheapest of this option is Electric Brakes, but there are other options.

From there, the next decision is what axle combination your budget will allow.
40mm square with Holden bearings are 1000Kg per axle.
45mm square with Falcon bearings are 1400Kg per axle.
50mm square with Falcon bearings are 1500Kg per axle.
50mm square with Parallel bearings are 1600Kg per axle.
50mm square with 2 Tonne bearings are... yep, 2000Kg per axle.

Now, the reason I've stated the above "per axle", is that the combination of both axles and suspension effects your overall GTM. With non load-sharing suspension (slipper), the axles must have a rating above 120% of the GTM, so a 2000Kg trailer requires axle with a rating higher than 1200Kg.

Lastly, if you do build a trailer rated higher than 2000Kg, there is a big jump in price once you go from 10" to 12" Electric. The 10" brake is good for 1600Kg the pair, and the 10" drum is what the Parallel bearings were built around. However, the front snout diameter of the Parallel drum will limit your stud pattern/wheel choice. Be careful of factory alloys too, that a), they fit over the snout of the drum & grease cap, and b), they are rated high enough.

Hope this helps.

Thanks for the help so far guys.

So let me know if I am on the right track for a GTM of 3500kg...
75X50X3mm RHS for the frame and 100X50X4mm RHS for the draw bar. What about the actual tray frame as per Rod's trailer?
50mm square axle with 2 Tonne bearings
Electric brakes on both axles


I have no experience with electric brakes so I am assuming I am going to need a controller in the ute? How much are they generally installed?
What ratings do Rocker springs normally come in?
What sort of a budget should I allow for a build like this?
What would be the chances of getting the tare weight under 764kg?
What would be a rough price difference between 10" and 12" brakes?
What is involved with breakaway brakes?

Maybe I should aim at a GTM of 3200kg if it would be significantly cheaper. That way I would use the parallel bearings and 10" brakes.

Originally Posted by Yonnee

\
The next step back is 2000Kg GTM. This is the point at which brakes are required on ALL wheels, and well as the ability for the brakes to apply themselves should the trailer become detached from the tow vehicle. By far the cheapest of this option is Electric Brakes, but there are other options.

Just to clarify... You can build a trailer up to 2000kg with brakes on one axle and a hydraulic overide setup. I'm pretty sure this is what you meant Yonnee but I took it differently the first time I read it.

Personally if you don't have a specific job that needs a trailer with a capacity over 2000kg I would just build to that as the jump in cost of components above that is dramatic not to mention the fact you need to go to electric brakes with a controller.

And have a look here for ideas of cost

Trailerparts Kit

4000kg tandem kit about $3800
3000kg tandem kit about $3000
2000kg tandem kit about $1500

Originally Posted by gallegos

Just to clarify... You can build a trailer up to 2000kg with brakes on one axle and a hydraulic overide setup. I'm pretty sure this is what you meant Yonnee but I took it differently the first time I read it.

Correct. Probably a little confusing as I was going backwards in weight capacities.

Originally Posted by gallegos

Personally if you don't have a specific job that needs a trailer with a capacity over 2000kg I would just build to that as the jump in cost of components above that is dramatic not to mention the fact you need to go to electric brakes with a controller.

The cost isn't really that different. The difference between an electric axle and a hydraulic axle is similar to the cost difference between an electric coupling and a hydraulic coupling (one almost outweighs the other). And you can pick up a good Tekonsha controller for well under $100.00 these days.

Originally Posted by naddis01

Thanks for the help so far guys.

So let me know if I am on the right track for a GTM of 3500kg...
75X50X3mm RHS for the frame and 100X50X4mm RHS for the draw bar. What about the actual tray frame as per Rod's trailer?
50mm square axle with 2 Tonne bearings
Electric brakes on both axles


I have no experience with electric brakes so I am assuming I am going to need a controller in the ute? How much are they generally installed?
What ratings do Rocker springs normally come in?
What sort of a budget should I allow for a build like this?
What would be the chances of getting the tare weight under 764kg?
What would be a rough price difference between 10" and 12" brakes?
What is involved with breakaway brakes?

Maybe I should aim at a GTM of 3200kg if it would be significantly cheaper. That way I would use the parallel bearings and 10" brakes.

I'm still at work at the moment, so I'll answer this with more detail tonight, but you are on the right track for 3500Kg, and yes, it would be significantly cheaper with 3200Kg.

Good controllers, the pendulum type, can be got for under $100.00 now, and installation depends on how thorough and neat the installer makes the job and what sort of vehicle it's fitted to. If you have more than one tow vehicle, then consider a controller like the Tekonsha Podigy P2. It mounts in a cradle which not only allows removal, but transition from vehicle to vehicle by installing a second cradle.

Load Sharing (Rocker) suspension comes in many forms, ranging in ratings from 2000Kg through to 8000Kg. The lighter duty kits come as an eye/eye set of springs with shackles either at the rear of each spring, or at the centre pivot. My suggestion for yours would be the Rocker Roller style of kit in which each spring has an eye at one end, and an elliptical loop at the other containing a steel roller. I would also recommend a 7 leaf kit, as this is designed to have 3000Kg on it all day every day, and some rate it as such, but I've seen ratings by the manufacturer of 3500Kg for the same kit. Whatever the rating may be, this kit will be fine for the 3200Kg you'd rate the trailer.

The price difference between the axles and brake will vary depending on whose axles, whose brakes, and whether you deal with a third party. When I was at Melbourne Trailer and Caravan Supplies, who were/are manufacturers and the Australian distributor for Dexter brakes, the price jump from a 1400Kg 10" Electric to a 2000Kg 12" Electric was roughly double, with the 1600Kg Parallel about halfway between. And if you do deal direct with a company like them, you can tailor your axle widths to your requirements as they will make to order.

Breakaway is as simple as a kit fitted to the trailer which has a battery and a switch, that are spliced into the trailer's brake wiring. The switch is a simple device with two wires, one in, one out, and a plastic plug attached to a cable. The plug keeps the internal terminals of the switch apart and the cable is attached to the tow vehicle (generally not to the same place as the chains). If the trailer should ever become detached from the tow vehicle, the cable pulls the plug from the switch, the switch then closes the contacts, providing battery power to the trailer's brakes. You'll need to check with RMS about NSW's "extra special" requirements where the Breakaway battery not only must have a charging system, but a battery monitoring system in the tow vehicle, neither of which are a Federal requirement in the VSB1.

Finally, if you've towed before, but never with Electric Brakes, you will find the difference is like chalk and cheese. Mostly it's the control you have from the driver's seat rather than the trailer pushing you from behind to apply its own brakes.
I will never, ever, own a trailer with Over-ride brakes again.

Thanks again guys.

Originally Posted by DaveTTC

My trailer has an empty weight of 620 kg and is engineered to 2400kg total weight from memory.

It has Toyota rims 14" I think.

It is a 12' x 6' flat bed. Tows beautiful and have been using it for since 96. I swapped it for a car.

The drAw bar is about 6' beyond the tray.

If you would like photos I can post some tomorrow or Wednesday.


Dave

The Turning Cowboy

I don't know how I missed your post Dave but feel free to post pics.

Originally Posted by naddis01

Thanks again guys.



I don't know how I missed your post Dave but feel free to post pics.

Ok up in Sydney ATM. Will post some over the weekend.


Dave

The Turning Cowboy