Treg coupling and weight distribution systems

Was in a van park a few weeks ago and there was a big Kedron with a treg hitch and they were using a WDH and said they had no trouble.
Incidentally Air bags are not a substitution for a WDH.

While they appear to level the vehicle, they dont and cant transfer the weight back onto the front axle that is lifted off by the action of putting the weight on the towball.

Why can't you use WDH with a Treg coupling ?

My understanding is that while you can use a WDH with Tregg, but must uncouple it when offroad as the WDH limits the articulation (eg if you try to drive across a wash-out, or over a ridge).
We have towed a variety of off road rigs (latest is 2.4 ton) over the last 22 years and never used a WDH.

As the WDH transfers weight (from the ball) from rear wheels to front , perhaps a simpler solution is to have the correct weight on the ball ? (but then I have never used WDH, so there may be other reasons for them.)
.............Keith.

We have had offroad van with treg coupling since 1997. Van has been towed over 100,000km in that time. We've had a Hayman Reese WDH the whole time - think we got ours just as they started to make them to go with tregs. We do take it off if we are going on dirt roads, but always use it on the bitumen. We also have polyair bags inside the vehicle's rear coil springs, but that is to extend the life of same, in theory and improve our ride.

Let me rephrase that last question- how much does the measurement at the front wheels change, and how far from the road surface is the centre of the towball when the trailer is attached. it must be between 350 and 460mm to be legal.

Hi David,

I'm not sure of your source, but the centre of my towball is 480mm.

My tyres and suspension are standard, and the towbar/tongue/ball is genuine Toyota. Measurement taken with 0psi in the Poly's.

When towing a light trailer the drawbar does not compress the rear suspension at all.

Not discounting your claim on heights, but all my gear is OEM and therefore should be compliant.

I am a Tow-Ed Instructor, my reference is trailer laws. I will try to find a direct reference for you shortly.

Oh how I wish OEM stuff was compliant. 30% of the stuff I see is not.
I had a 4.5 tonne ATM trailer the other day, brand new with 3500 kg hitch, tyres with a total combined load rating of of 3600kg and numerous other issues.

"The National Code of Practice Building Small Trailers"
12.2.1 50mm Ball Couplings
Ball couplings used on trailers with an ATM of up to 3.5 tonnes must comply with Australian Standard AS 4177.3-1994 and be installed so that the height of the centre of the body of the ball coupling is between 350mm and 420mm from the ground when laden.

All of that aside, if the height does not change when loaded, you do not need a WDS as your front ride height and steering geometry is unaffected

Sorry I should read what I cut and paste, bit too busy sometimes. The law above changed recently and is now 350 to 460mm.

This legal, not legal argument was done to death on a Caravan Forum and the end result was, I believe, that those regulations concerning towball height did not apply to off road trailers, caravans etc.

Hi Gone Bush,

I was not privy to those discussions on other fora, but you are correct re my use of the word legal, may be an overstepping of the mark.

I and others in the game take advice from various guides and standards and laws, and as I and others in the game see it, the Code is not itself enforceable as law, but should you depart from it, you may find yourself being found out on a legal limb.

The Guide is for Light Trailers and very light trailers which is by definition

A trailer with a ‘Gross Trailer Mass‘ not exceeding 3.5 tonnes
A single-axled trailer with a ‘Gross Trailer Mass‘ not exceeding 0.75 tonne.

So caravans and off-road trailers would seem to fit.

Anyhow, getting back to the original question. To determine if a WDS is required, you first must consult the vehicle manufacturer's specs, available from us at Tow-ED or from the RACQ in this state, then consult the trailer manufacturer, then check the actual ride height change. It is recommended you do this intially at the towball, with refernece to the National Code as above, then use the measure of front ride height to set your WDS. Never use a WDS to compensate for incorrect towball downforce. Tow ball downforce should be 8 to 12% of trailer mass (10% recommended) and should be within the vehcile and towbar manufacturers limits.

I believe the towball height as mentioned only applies to ball style couplings and not to tregs, AT35 etc

And this was discussed in detail in a previous post


65373

Thanks for the information, David.

I've been away on a work trip for a few days, hence the slowness in my reply.

In your reference to 12.2.1, I suspect that is the standard for construction of the trailer, as opposed to the towing vehicle.

It would be commonsense, however, to set the height of the hitch on the towing vehicle to that of the coupling on the trailer (in a level attitude).

That's the good thing about the Reese WDH, it has a broad range of height and angular adjustments so you can do just that.

Thanks again.

hi Jarse
I Totally agree My 03 Prado does the same thing my Avan Liam adventure mk 11 is the same weight gvm 1990 kg TWO axles , the steering and corning are not as positive
Terry

Actually the guide has a #1 note (WDS required) on the 2300kg max limit but not on the 750 kg so my interpretation of that is that WDS is required for 2300 kg but not for 750kg