Thread: Trailer drawbar length

Hi All,

New member, first time poster and first time trailer builder!!

Im taking on what i call a "man project" to build a trailer...something along the lines of trying to balance qualifications (head) with skills (hands). Im going for a sub 750 kg, no brakes, with fibreglass canopy to be used mainly to go camping etc. Hoping for some good advice from the old hands in this forum.

Anyway i picked up a '88 Triton single cab ute tub for $200 bucks and away i go. I liked that tub as the wheel arch is set 20 mm back from centre of the inner tub space. Its (outer) dimensions are 2350 x 1600 mm, and ive figured if i put the axle just slightly rear of the the centre of the wheel arch i have a longer distance to the front of the load area than from the axle to the rearmost point (overhang). If i understand VSB01 correctly, such a configuration would be compliant. What i miss out on the is the rule of thumb of the 1/2" for every foot of load length... which i gather relates to ball down pressure and handling at speed.

To compensate for this I gather ive got two options - put on a tool box in front of the tub or have a long (er) drawbar (oh, both of them is the 3rd option). I anticipate the trailer (without the drawbar) will weigh 300 kg (200 tub, 50 springs/axle set, 30 steel frame - 50 x 50 x 2 RHS, 20 alloy wheels). I plan to make the drawbar from 75 x 50 x 2.5 RHS. From what i observe of many rental trailers the coupling sits ~ 1.25 m from the box. I was planning 1.4 m (being 30 cm for possible tool box, then spare mount and ~ 1 m clearance in case of jack knife to body of the car) with the drawbars running back to the first spring hanger. Will this be sufficient? Will i need a tool box etc, and if so how much 'ballast' does it need?

PS I am aware not to weld across the drawbar and will make sure the welder knows this also.

Cheers Chris.

Hey Chris, and Welcome.

Sounds like you've been doing your research... Excellent!

Firstly, one thing to be mindful of with your 750Kg limit without brakes, is that a decent trailer can weigh somewhere around 300-350Kg. Add to this 50-75Kg of fibreglass canopy, and a spare wheel, doesn't leave alot of room for payload. Depending on what car you're towing it with, and how far you intend travelling with it, even 750Kg will increase braking distances quite substantially. If budget is an issue, when you buy an axle, get the brake mounts welded on during manufacture. Even if you dont end up adding the brakes themselves, the cost is bugger all to do it at this stage. Then if you do find that you want to add brakes, it's much easier and cheaper if the mounts are already there.

As for your wheel arch set back, while it's not the perfect "rule of thumb" placement, at least it's actually behind centre! Plenty of blokes make trailers from Dual Cab tubs, and they are a nightmare on wheels! (And technically don't comply with VSB1, as the rule states that the axle must be behind the centre of the loadspace.) If placing the axle slightly behind the centre of the arch still looks ok, then every little bit will help. I would plan to put a spare wheel on the trailer, either vertically in front of the tub/toolbox, or horizontally tucked in the 'V' of the drawbar, and this will compensate for the axle placement.

Thirdly, I will always recommend a longer drawbar, without question! The longer the drawbar, the easier it is to reverse a trailer, no if's, no but's. Generally, mass produced trailers are made to a price, so the less steel, the less it costs them. 4' is usually the minimum, as most tow vehicles are less than 8' wide, and therefore, the front corner of the trailer won't hit the tow vehicle if you jack-knife it. If you plan on adding the toolbox, then I'd suggest at least 5'6" from the front of the tub. But you could go back to 5' if you only made a toolbox as wide as the drawbar.
Don't go 2.5mm on the drawbar, minimum 3.0mm.

Hope this has helped. And good luck. (Don't forget to put up progress pics for us all to enjoy. )


Yonnee.

I think Yonnee has answered everything that you need to know but I'll chuck my $0.02 in as well. I think having a tool box and spare on the draw bar is a good idea(can't have too much storage in a camp trailer), I have both on my box trailer that I take camping and since having them I wouldn't have a trailer without them. One thing to do is to make sure you have enough room from your spare to hitch so if you jack knife it doesn't hit your car. I added a spare to my box trailer after it was built and it hits the tray of my ute (tray back) sometimes, It's a very tight fit where I keep my trailer and I have to jack knife it to get it in there. So to sum it up I'd say 1.2m from spare (assuming you went -tray-tool box-spare-) to hitch and put brakes on the trailer as well, trailers get hevy fast. And plenty of picturs of your progress as well.

Thanks for the replies guys. Im OS at the moment so sorry for the slow reply.

Hmm... Looks like the *second* trailer i build will be pretty awesome. Im happy that this is a learning process for me also.

Basically im already committed to 1T axle and springs, and my budget doesnt yet stretch to brakes. Does it make sence to have brake mounts welded onto that? My camping equipment currently fits into two 60 kg roof boxes + 4 bikes, so im going to have to live with (and should be ok) 750 kg for a while.

Will do 3mm for the draw bar, and make it > 1.5 m. Roughly the A frame pieces will be 2.5 m long, so x2 + 0.4 m brace ~ 5.5 m long @ 5.4 kg/m so approximately 30 kg in the drawbar. With a spare on the A frame im guessing (though will calculate it) ill have 30kg on the ball for an empty (300 kg ish) trailer. How does that sound?

I plan to post lots of pictures and boring details, as i want a record of the build. Probably parallel posting in myswag.org forums. My goal is to get it on the road quickly, and then make refinements and improvements as time goes on.

Cheers Chris.

I'm looking forward to the pics.

I know you already have the ute tub but I sometimes wonder how much heavier they are than just building a normal box from scratch.

Maybe they aren't heavier.....what does a tub weigh?

Id only be guessing at 200kg for the tub. Me and a mate were able to lift it and move it... not that easily.

The trailer will definitely not be light!

Has anyone got some good pictures of how they have mounted their drawbar onto the frame. I am currently building a dual axle trailer and am looking for a few suggestions. Thanks

Go to Yonnee's post a few places above this one and follow the link to his trailer build.

Follow his lead and you won't go astray.

Originally Posted by murray44

I'm looking forward to the pics.

I know you already have the ute tub but I sometimes wonder how much heavier they are than just building a normal box from scratch.

Maybe they aren't heavier.....what does a tub weigh?

I had a trailer made out of a BA Falcon ute tub. From memory the trailer weighed 450kg so it only had a payload of 300kg.

I am currently on the hunt for a PX Ranger (current model) single cab tub to make another trailer out of.