Outer Limits 4x4 Board

Ok so i have been thinking about making another trailer. Flat bed, folding sides and a 4.5T load limit.

Now i have been towing a large spray tanker with a tractor and all the trailer has is a 2 axles/hubs on each side. One of each end of a solid beam and a pivot in the centre (no other suspension). It keeps the trailer unbelievably level over some very very rough terrain.

This design is used quite often for atv and low speed trailers (forestry) not used on road? The only problem i can see is that if the load is not centred over the pivot point correctly the more weight will be put onto the towing vehicle and not supported by a spring on the trailer.

Also i dont see breaking as a problem, i thought that the breaking of the front wheel would force the rear wheel to rotate upwards (foward rotating force on one end of the beam would result in an upward force at the other end of the beam). But even this shouldnt be a problem as to lift the rear wheel it would have to lift the whole trailer.

Anyone else have any thoughts on it?

Here is a pic that shows the beam and pivot. It wont have a high lift central arm, just enough for clearance of the wheel and some travel.

Dosent this system used a fixed draw bar point ?

Eg minimal up and down movement as to keep the trailer attached.

The spray cart we had our farm did and was a pain driving over colvert drains because of this.

Can you get a pic of the attachment ?

Cheers Nick

CWBYUP wrote:Dosent this system used a fixed draw bar point ?

Eg minimal up and down movement as to keep the trailer attached.

The spray cart we had our farm did and was a pain driving over colvert drains because of this.

Can you get a pic of the attachment ?

Cheers Nick

Fixed draw bar point? I was just going to use a tow ball and hitch. It should be able to have as much up and down movement as the tow hitch will allow. I think the problem with your attachment would be because it is so low and would catch on the colvert. This would be fixed by a conventional height towbar. Is that what you meant?

G'day mate,

Are you planning on having it registered. Im not entirely sure as i am no trailer manufacturer, put possibly the break system you will require is what is going to influence how your suspension/axles will be setup. I will be picking up a 4.5 tonne tri-axle boat trailer that has just been built this weekend. It is running 2 parabolic leafs, side by side, at each wheel and the parabolics are all connected on some funky rocker type arrangement that the builder has built. After much research this combination was the largest, heaviest duty running gear setup that we could find.

I can take some photos of the arrangment and post them up if you are interested in some other design ideas to kick around.

KaMo wrote:G'day mate,

Are you planning on having it registered. Im not entirely sure as i am no trailer manufacturer, put possibly the break system you will require is what is going to influence how your suspension/axles will be setup. I will be picking up a 4.5 tonne tri-axle boat trailer that has just been built this weekend. It is running 2 parabolic leafs, side by side, at each wheel and the parabolics are all connected on some funky rocker type arrangement that the builder has built. After much research this combination was the largest, heaviest duty running gear setup that we could find.

I can take some photos of the arrangment and post them up if you are interested in some other design ideas to kick around.

Kamo, the setup you are running is fairly std for leaf sprung trails with the shackels connected, as it also shares the load between each axle as you move over a bump very well.

You can buy the stub axle and break setup and have it welded through the beam no worries.

Adam, I am nbo expert, but I imagine the set up you are reffereing to is really set up for very slow work only, I dont think there would be much chance of getting it passed for road use, maybe have a chat to a trailer menafacturer

I know exactly what you mean tiny, if i was an engineer or trailer manufacturer i would be a little iffy about it being used for hi speed use. Im just trying to figure out why it isnt good for hi speed....

if i was making a car trailer, i'd be making it like that, it gives you a lower c.o.g. we had a hammer mill/mixall on the farm with the same axle setup, it was good for 40kph, fastest the tractor would go.
i cant see it being a problem, as long as the wheels were in line.

For a braked wheel it's not a good design. The braking torque on the front wheel causes the rear wheels to unload, in the extreme case for the pivoting suspension link to rock forwards until it tops out on it's stops (or flips over if it has no stops).

To get brakes to work well on this design you either need very long levers to minimise the load shift or a parrallelogram floating brake design to take the brake torque out of the pivoting link.
This is what aircraft do on their landing gear.

Another consideration is suspension that may be necessary to meet road regulations (not a difficult problem, just a consideration).

with the brakes, why not run a bias valve, like 60/40, the back wheel getting more pressure than the front.

rover1 wrote:with the brakes, why not run a bias valve, like 60/40, the back wheel getting more pressure than the front.

It could help, but you'd be taking the braking force from the wheels where it did the most good.
Lowering the pivot point will help a lot, but on an offroad trailer that usually goes against the original goals.

imagine what happens at 100 kph when you have a blowout/wheel failure on the front tyre...

you ask how I know this ---- mate had this setup on a huge scarifier

made a big mess when a front wheel stub failed,,,,,,,,



(would be different if spring loaded somehow....)