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  1. #1
    Join Date
    Nov 2017
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    Geelong, Australia
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    57
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    2,651

    Default 3.5T Flat deck trailer build

    I've decided its about time I built myself a decent trailer to cope with the jobs that are too large/heavy for the ute.

    So far I've mostly managed to get away with borrowing a mate's 10x6 box trailer (2T override brakes), or for moving vehicles I've hired car trailers.
    Problem with most hire car trailers is they only have a payload of around 1200kg, so nowhere near legal to carry your average dead Landrover which is my usual requirement.
    For the record they are typically ones that I've bought or been given already dead - they haven't died on me
    The tow vehicle is always one of my Landies, and whenever possible its my old 1985 Isuzu powered 110 "County".
    They are all rated to tow 3500kg.

    So....some basic requirements:
    • 3.5T ATM tandem - so electric brakes on both axles + breakaway coupling.
    • Strong, but not overbuilt as I want to keep the load capacity as high as practical (2700kg seems reasonably achievable)
    • Around 4.5m long load space
    • Minimum 2m width load space


    I then tossed up as to whether to go for a traditional style car trailer with the deck lower than the mudguards, or a full width flat deck with wheels underneath.
    Lower deck is much easier to load for vehicles or if you were winching up ramps etc, but the mudguards above the deck make it a pain to load anything else from the side unless you're slinging it.
    Flat deck is much easier for loading from the side with a forklift, but higher CofG.
    At this point I'm thinking flat deck, but not set in concrete.

    Found this design online: https://www.trailerplans.com.au/prod...t-top-trailer/
    And then found this build to the same basic design, but with a beavertail section at the back.
    4.8m (including the beavertail) x 2.4m load space which is about perfect for what I want. I could go shorter, but then the beavertail gets shorter/steeper or the flat load area gets smaller. It seems to be a pretty good compromise as-is.
    I wouldn't bother with permanently attached ramps or headboard/toolbox etc.

    I forked out the $55 and bought a set of plans. They are quite comprehensive, and a good summary including all the wiring and light requirements etc as well as good construction techniques etc. Even if I don't end up building that design having all that info in one place is worth the $50 IMO.
    Main chassis rails and drawbar are 150x50x3 RHS, and the deck structure is 50x50x3 with 2mm black sheet for the deck itself.
    The structure is pretty simple - I guess aimed at the non-professional builder so isn't full of triangulated gussets etc.

    Time for some constructive criticism or suggestions from you guys

    Steve

  2. #2
    Join Date
    May 2011
    Location
    Murray Bridge S Aust.
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    Default

    Quote Originally Posted by OxxAndBert View Post
    They are all rated to tow 3500kg.
    So....some basic requirements:
    • 3.5T ATM tandem - so electric brakes on both axles + breakaway coupling.
    • Strong, but not overbuilt as I want to keep the load capacity as high as practical (2700kg seems reasonably achievable)

    Lower deck is much easier to load for vehicles or if you were winching up ramps etc, but the mudguards above the deck make it a pain to load anything else from the side unless you're slinging it.
    Flat deck is much easier for loading from the side with a forklift, but higher CofG.

    Main chassis rails and drawbar are 150x50x3 RHS, and the deck structure is 50x50x3 with 2mm black sheet for the deck itself.
    The structure is pretty simple - I guess aimed at the non-professional builder so isn't full of triangulated gussets etc.
    Time for some constructive criticism or suggestions from you guys Steve
    Hi Steve,
    All your planning and plans are OK, instead of the 50X50X3 all the way through, I'd run them where your sheets join, then use 50X25X2.5 for the rest, you could get away with 2.5 for the 50X50 also, which will help cut down on the tare weight, which I think would run to about 1100kg. I'd also use Duragal, as you won't have to constantly paint it to keep it looking good.
    I'd also put checker plate on the floor, as it will help with something to grip, tyres or feet if you have to push off a Landy. It can be galvanised before fitting to the trailer, if you do, INSIST that it be Australian checker plate steel, as the Chinese stuff will have more curves and bows than a Hula Girl. DAMHIKT
    To help keep the CofG down, you could run smaller wheels, 13's are about as low as I'd go with LT (Light Truck) tyres.
    You haven't mentioned the type of suspension that you intend to run, I'd go with roller rockers, and 9 leaf springs as they will carry the load without a problem.
    Let me know if I can help getting any of the components, to bring over when I pick up the Mill???
    https://www.rivercitytrailers.com.au/ If you scroll down to some of the staff, that's me standing next to the boss, he's in the shorts.
    https://www.rivercitytrailers.com.au/flat-top-trailer Here's a link to our basic flat tops to give you an idea.
    HTH
    Kryn
    To grow old is mandatory, growing up is optional.

  3. #3
    Join Date
    Nov 2017
    Location
    Geelong, Australia
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    Default

    Thanks Kryn.
    The plans show the 50x50x3 floor supports at 600 centers, but sounds like you'd expect there to be more?

    Checker plate floor instead of plain - I'm still undecided on whether to go that way or not. Agreed it gives a better footing, but harder to move things around....

    I was looking at this sort of roller rocker kit for suspension: https://www.huntsmanproducts.com.au/...gineered-axles
    They are only 7 leaf though - not 9 like you suggested??

    Re wheels/tyres - I was thinking about 195R15L/T's which are rated at 950kg each. The smaller diameter 13/14" wheels/tyres seem to be right up at their maximum capacity for 3500kg if the trailer is perfectly loaded, and would be easy to be above that with a bit of uneven load side-side. I'd prefer to be running slightly less than their max capacity - hence using the 195R15. I'll be buying new tyres - just not worth messing with old tyres of unknown history that will be run near their max load.

    Edit: fixed the tyre profile - incorrectly had 195/70R15

    Steve

  4. #4
    Join Date
    Jun 2005
    Location
    Helensburgh
    Posts
    618

    Default

    I would use the flooring that is used on car carriers because it has slots in it for tying down vehicles at each wheel. A question, does a trailer build like this have to have engineering certification to get a VIN plate?
    CHRIS

  5. #5
    Join Date
    Jan 2004
    Location
    Mackay North Qld
    Posts
    6,446

    Default

    Hi Steve ,
    Maybe you have already ready perused the info in the link and maybe you haven't.

    No matter it might be useful to those who are about to build a trailer.

    The underlying message is to have the trailer completed and registered by June 22

    https://metalworkforums.com/f184/t12...ng-regulations - scroll to end

    It would be awful to have poured effort and capital into a trailer to have it refused registration.

    Hope it helps

    Grahame

  6. #6
    Join Date
    Nov 2017
    Location
    Geelong, Australia
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    Default

    Thanks Grahame.
    Yes, I've had a good read into that link, and its part of the reason I've decided to do it now.

    Chris, my understanding is that currently (ie prior to July 2022) it doesn't require separate engineering certification as long as it complies with VSB1 rev5.
    The trailerplans.com plans are stated as being compliant, but you wear the responsibility for the quality of construction firmly on your own butt cheeks
    While that car carrier flooring would be great for a dedicated trailer that only carried vehicles, I think it would be a PITA on something that's designed for more general use so won't be going that direction.

    Steve

  7. #7
    Join Date
    Jun 2005
    Location
    Helensburgh
    Posts
    618

    Default

    Quote Originally Posted by Grahame Collins View Post
    Hi Steve ,
    Maybe you have already ready perused the info in the link and maybe you haven't.

    No matter it might be useful to those who are about to build a trailer.

    The underlying message is to have the trailer completed and registered by June 22

    https://metalworkforums.com/f184/t12...ng-regulations - scroll to end

    It would be awful to have poured effort and capital into a trailer to have it refused registration.

    Hope it helps

    Grahame
    Grahame, most of the links in that page need to be removed as they no longer work.
    CHRIS

  8. #8
    Join Date
    May 2011
    Location
    Murray Bridge S Aust.
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    Quote Originally Posted by OxxAndBert View Post
    Thanks Kryn.
    The plans show the 50x50x3 floor supports at 600 centers, but sounds like you'd expect there to be more?
    I was looking at this sort of roller rocker kit for suspension: https://www.huntsmanproducts.com.au/...gineered-axles.
    They are only 7 leaf though - not 9 like you suggested??
    Re wheels/tyres - I was thinking about 195R15L/T's which are rated at 950kg each. Steve
    Hi Steve,
    We have our centres at 300, the floor doesn't seem to bend when a vehicle is placed there.
    Will see if I can get a better price for you??? Something the size you're after, I'd go parallel bearings, they use Ford inner bearings on the inners and outers, rather than Fords small on the outer. I feel that with the small outer, you'd be getting close to the max with not much to spare.
    12" electrics would give you plenty of stopping power
    The reason I suggested the 13" wheels was to get the CofG down lower.
    To help with tying down, you could use these, https://www.transporthardware.com.au...ng-heavy-duty/ 1850kg capacity. Bolted into the floor, you'll have no problems tying down.
    HTH
    Kryn
    To grow old is mandatory, growing up is optional.

  9. #9
    Join Date
    Jun 2005
    Location
    Helensburgh
    Posts
    618

    Default

    Have a look at a car carrier, way more versatile than fixed tie down points and there are no compromises that fixed points always present.
    CHRIS

  10. #10
    Join Date
    Mar 2011
    Location
    Southern Flinders Ranges
    Posts
    1,536

    Default

    Might want to build it to Rev6 that was released Feb 21.
    For load restraint stuff have a look at tie downs direct, I bought a swag of aircraft style stuff off them earlier in the year, pricing, service and quality of the gear when it lobbed on my door was good.


    As far as the other commentary around not being able to owner build as of July I would check with the reg authority in the state you live in, not that I’m skeptic but there’s one post elsewhere on this forum, that contains a degree of interpretation and speculation and nothing in the way of supporting documentation. You know, because internet….

  11. #11
    Join Date
    Mar 2011
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    Southern Flinders Ranges
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    Default

    Quote Originally Posted by Chris Parks View Post
    Have a look at a car carrier, way more versatile than fixed tie down points and there are no compromises that fixed points always present.
    You’ve clearly never tried to lever a pallet across the stuff…

  12. #12
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    Nov 2017
    Location
    Geelong, Australia
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    Quote Originally Posted by KBs PensNmore View Post
    Hi Steve,
    We have our centres at 300, the floor doesn't seem to bend when a vehicle is placed there.
    Will see if I can get a better price for you??? Something the size you're after, I'd go parallel bearings, they use Ford inner bearings on the inners and outers, rather than Fords small on the outer. I feel that with the small outer, you'd be getting close to the max with not much to spare.
    12" electrics would give you plenty of stopping power
    The reason I suggested the 13" wheels was to get the CofG down lower.
    To help with tying down, you could use these, https://www.transporthardware.com.au...ng-heavy-duty/ 1850kg capacity. Bolted into the floor, you'll have no problems tying down.
    HTH
    Kryn
    Thanks Kryn.
    The bearings in that Huntsman kit are same as Alko 2T axles - 30210 AND 15123 bearings. Inboard bearing is 50x90x21.75 and the outer is 31.75x62x18.1 - so the outer is still smaller than the inner, but not like Falcon outer "small".

    I got where you were heading with the 13" wheels, but I haven't found anything online smaller than 195R15 that has a high enough load rating.
    It needs to be 875kg per wheel for the 3500kg total and seems even 14" wheels are only 850kg rated. Maybe I'm just looking in the wrong places!!
    I'd thought briefly about using Landrover hubs and wheels as I have plenty of spares, but not worth the hassle for a highway trailer. Better off just to stick with the common landcruiser pattern I think.

    For tie downs, I'm planning to run a 20NB pipe rail underneath the deck down both sides and hopefully most of the front. Its what I've got on my ute tray and I've found it very flexible. Rear and mid-deck will definitely need something like those tie down rings, but I really want to keep the deck as flush as possible. Do you typically just punch a hole through the deck sheet and drop them in from the top and bolt down, or mount them underneath the sheet?

    Steve

  13. #13
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    May 2011
    Location
    Murray Bridge S Aust.
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    You could still go with the Landrovers rims, that'll save a few hundred dinero's, to spend on another project.
    Any supplier SHOULD be able to do this, it'll save carrying a spare on the trailer also.
    20NB pipe should be sufficient tie down rails to hold a Landy down, we use 25 bent with a step at the front, have also done a few with steps both ends as well. Only reason we use 25, is cos you never know if people are going to use chain binders on them. Have seen one come back with the pipes really bent, I think they tied down a caravan on it!!! Side rails supported about 400-500 centres with 50X8 will stop any flexing. We put them on the back of the pipes, so that there's a 50mm gap between the side and tie rails along with some 75X5 to take the clearance lights, and it protects them at the same time. What size RHS are you using as the side/combing rails, I run the wiring through this for the side lights. Drill your holes at the bottom of the rail above the lights, saves adding more steel for wiring.

    The tie downs are usually just bolted down from the top, but there's nothing stopping you from machining/laser cutting pieces of 8mm to accept the hold down and fitting it under the floor and cutting out the floor to accept the hold down so that it is flush mounted, or even bolting it underneath, though it will flex more. If you do go down the plate method, tie them into the floor cross pieces, a LOT more support that way.
    In the A of the drawbar, you could put a piece of 1.6 sheet metal under the drawbar, and fit some ally 5 bar to the top to act as a toolbox for ropes, tie downs etc. saves making some for the sides of it. I find that side boxes are a pain as they're never big/long enough.
    You could also fit a winching receiver to the front, to help load a "failed to proceed Landy". Make it vertical and the floor will remain flush.
    Hope this will give you a few more ideas?
    Kryn
    Last edited by KBs PensNmore; 1st Jan 2022 at 02:14 PM. Reason: More details
    To grow old is mandatory, growing up is optional.

  14. #14
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    Southern Flinders Ranges
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    I prefer keyholes to drop chain in over the pull rings.

  15. #15
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    Quote Originally Posted by racingtadpole View Post
    I prefer keyholes to drop chain in over the pull rings.
    That was something I’d considered, but hadn’t come across a nice way of connecting a standard 2500kg ratchet strap.
    I was thinking short lengths of chain but the strap hooks won’t go through a chain link, and pretty sure a hammerlock would be too small too.
    Lug link would work but seems like overkill

    Steve

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