What can I legally attach to my tow bar?

[BLSTIC]

Well, that isn't a trailer anyway...

Say, for example that once a year I needed to do a road trip and there wasn't quite enough room in my AU sedan. I could easily (ish) build a thing that went where my 2200kg towbar can go, say a dirty great box kind of like an extra boot.

I know that bike racks that insert where towbars go are a thing, but I've yet to see anything else.

Are there any rules that prevent me from attaching a big box of loot, if it doesn't obscure the tail lights and I have one of those accessory plates on it?

[mike_nofx]

One restriction would be ball weight limit, as well as overall vehicle load carrying mass.

[Tonz]

Ive seen plates with wheel chairs on them

Originally Posted by BLSTIC

I could easily (ish) build a thing that went where my 2200kg towbar can go, say a dirty great box kind of like an extra boot.

The down weight over your axle is a different beast to the weight that your car can pull. It will massively alter the weight distribution of your car and its handling, particularly with your dirty great box hanging so back past your rear axle, it's likely to become a leverage point that reduces the weight on your front end which ends with you losing steering and crashing.

I've no idea legally what the rules are but perhaps start at Vehicles Standards of Department Transport & Main Roads (if you're in QLD), as well as the Australian Design Rules. If they can't answer it, they may be able to direct you to the place who can.

Why all that when you could get a trailer though? Or one of those ugly-as-sin roof boxes?

[Raptor]

It's not a new idea.

http://www.arkcorp.com.au/p/3452/hit...-cargo-carrier



OR

https://www.thule.com/en-gb/au/cargo...cargo-carriers

[arronm]

True and ideally you would pull a trailer behind that. Made my rack in the mid 90's. Used it 100s of times.

Replace bike with box...

[jpd80]

Originally Posted by BLSTIC

Well, that isn't a trailer anyway...

Say, for example that once a year I needed to do a road trip and there wasn't quite enough room in my AU sedan. I could easily (ish) build a thing that went where my 2200kg towbar can go, say a dirty great box kind of like an extra boot.

I know that bike racks that insert where towbars go are a thing, but I've yet to see anything else.

Are there any rules that prevent me from attaching a big box of loot, if it doesn't obscure the tail lights and I have one of those accessory plates on it?

Yep,
QDOT has front, rear and side projections (or overhang) allowed for the vehicle
so depends on the size and weight carried. Breach those limits or if cop thinks it's wrong
and it's an on the spot fine so make sure it's an approved design like the ones above.

[mike_nofx]

Anyone know the payload of an AU sedan?

[BLSTIC]

Originally Posted by leesa

The down weight over your axle is a different beast to the weight that your car can pull. It will massively alter the weight distribution of your car and its handling, particularly with your dirty great box hanging so back past your rear axle, it's likely to become a leverage point that reduces the weight on your front end which ends with you losing steering and crashing.

That may be true, but without the extra mass of the trailer pushing you (assuming you have no brakes on a lightweight trailer or override brakes on a heavy one), the handling would be much better with a box rather than a trailer if you, say, braked and turned at the same time.

Still, too much payload (even without the extension) means the car drives nose-up, which is not ideal. Ideally I'd have the fat people in the front, the skinnies in the back, and lightweight, high volume luggage for this to work without changing the rear springs. Because I'm not keen on getting pair of springs and shocks made just for a road trip... I hadn't thought of that until now.

Originally Posted by leesa

Why all that when you could get a trailer though? Or one of those ugly-as-sin roof boxes?

That's a fair question. I have a few of reasons, none of which are perfect.
1: I hate reversing with trailers, especially short ones. Box makes the car longer though, which still makes parking harder.
2: I like aerodynamics. I *could* build an aero trailer with a 400kg payload that could be towed by anything with a towbar, but it still wouldnt be better than sitting a box snugly in the wake of the car, which would add basically zero aero load at speed.
3: The boxes are good for extra capacity, but not aero enough for my liking, even the aero ones. Roof racks themselves are pretty bad, although that can be fixed. Perhaps I could make a super aero roof box, but it wouldn't be as good as a towbar box, and it wouldn't be able to carry as much as even a normal roof box.

[BLSTIC]

Originally Posted by jpd80

Yep,
QDOT has front, rear and side projections (or overhang) allowed for the vehicle
so depends on the size and weight carried. Breach those limits or if cop thinks it's wrong
and it's an on the spot fine so make sure it's an approved design like the ones above.

Thanks for that. Searching the QLD Transport site revealed that rear overhang limit is 3.7m or 60% of wheelbase, whichever is less, measured from the rear axle (or centre of axle set if dual/triple/whatever). At a guess that gives me somewhere between 0.5 and 1 metre of length I can tack on to the rear bumper on a car like the Falcon.

[naddis01]

I've seen Elders vehicles getting around with dog boxes on the back.

One thing to consider is the rated tow ball weight is measured at the tow ball. If your box of say 500mm further back from the axle, that rating would reduce significantly.

[Blue Dog]

Ask this bloke, he would be able to advise you...............

https://www.4bc.com.au/you-wont-beli...get-away-with/

[prydey]

Originally Posted by leesa

that reduces the weight on your front end which ends with you losing steering and crashing.

this is not entirely true. as the weight distribution moves rearward, weight does indeed come off the front axle, but this doesn't mean you lose steering. the effectiveness of the tyre is related to the downward pressure on the road in relation to the load it is carrying. the less the load, the less downward pressure it needs to do the same job.


as for hanging a load off the towball, providing it meets all the legal requirements, the only other things you need to keep in mind is the cars GVM, Rear axle load limit and towball weight limit.

bear in mind, the further behind the axle you put weight, the greater the multiplication effect of that weight on the rear axle. Ford (for territory at least) say that for every 10kg you put on the towball it adds 14.5kg to the rear axle.

[BLSTIC]

Originally Posted by naddis01

One thing to consider is the rated tow ball weight is measured at the tow ball. If your box of say 500mm further back from the axle, that rating would reduce significantly.

It would be nice to know how much of that towball weight is structural reasons and how much is handling reasons. But if I can keep it around that limit I'm sure it would be fine. A tailbox is going to handle far better than an unbraked trailer.

[commodorenutt]

Originally Posted by BLSTIC

A tailbox is going to handle far better than an unbraked trailer.

For the same payload, no.

Consider the dynamic load of the box too - it's way back behind the axle, adding to the "pendulum effect" like a rear-engined car.

You cannot exceed the towball load limit - which is 230kg for a Hayman Reese 2300kg hitch. As pointed out above, this will end up being de-rated based on the distance out from the back of the car.

So let's say you're wanting to carry 200kg. 200kg in a box, 200kg in a box trailer with a tare weight of 250kg (so a total gross of 450kg).
The box trailer is still the better option.

200kg hanging over the back like that will also handle far worse than towing a 450kg unbraked box trailer, as you're adding weight onto the vehicle - but in a box trailer the weight is over an axle, not on the car, so it's only a pushing/pulling load without the downforce of 200kg on the ball.

The trailer's suspension will support the load over bumps, dips & undulations, isolating the downforce of the load from the tow car. 200kg on the towbar, with the added leverage, will definitely reduce stability over the same road conditions, as it becomes the "tail wagging the dog" effect - the weight exponentially increasing up & down motion of the rear suspension over those bumps, and dramatically increasing the load. Put 300kg in the boot and see how it behaves.

[BLSTIC]

That weight limit is nice to know, the car has the heavy duty tow bar (not the trans cooler yet though, I'm going to fix that). I thought it was marked as 2200kg though, but it's probably the same part.

I'll have to try weighing down the boot. I imagine the biggest limit is going to be the rear suspension. As you imply, 300kg of extra load on the axle is a lot.

Trying to find the maximum weight of the whole car (GVM?) right now but can't seem to

[prydey]

Originally Posted by BLSTIC

That weight limit is nice to know, the car has the heavy duty tow bar (not the trans cooler yet though, I'm going to fix that). I thought it was marked as 2200kg though, but it's probably the same part.

I'll have to try weighing down the boot. I imagine the biggest limit is going to be the rear suspension. As you imply, 300kg of extra load on the axle is a lot.

Trying to find the maximum weight of the whole car (GVM?) right now but can't seem to

what is the car?

it doesn't matter what is stamped on the towbar. the manufacturer specs override that. you can't exceed the LESSER value.

GVM should be in the owners manual, along with max axle weights.

as above, a 6x4 trailer will be more stable in most situations, as you are adding an extra axle to help support the load.

[BLSTIC]

2002 (?) AUIII Forte SR, auto

Apparently the *UTE* is good for 2420-2740kg GVM

Originally Posted by prydey

this is not entirely true. as the weight distribution moves rearward, weight does indeed come off the front axle, but this doesn't mean you lose steering.

It was more of a worst case scenario if considering extreme circumstances. OP mentioned their 2200kg tow rating when talking about wanting to carry a load on top of their tow bar so it seems like they were considering trying to hang that much weight off the back of their car, which is way past its specification. Even a quarter of that weight is over spec. I can't see why else they would have mentioned the rating.

I think they're mistaking what they can pull via that bar versus how much down weight they can put on the ball.

Edit: Sort of confirmed by their earlier post

Originally Posted by BLSTIC

That weight limit is nice to know, the car has the heavy duty tow bar (not the trans cooler yet though, I'm going to fix that). I thought it was marked as 2200kg though, but it's probably the same part.

BLSTIC, you're venturing into unsafe territory. Your car can't carry 2200kg down on the ball. It can't even carry 500kg on the ball, even with a 2200kg tow rating.

[prydey]

Originally Posted by BLSTIC

2002 (?) AUIII Forte SR, auto

Apparently the *UTE* is good for 2420-2740kg GVM

if you have an owners manual it will be listed in there. however, it is likely you will have at least 500-600kg of payload. payload is everything that is added above the factory tare weight. Tare is the stock car plus 10L of fuel.

an AU had a max tow rating of 2300kg with a HD towpack, which gives 230kg max on the tow ball. If your tow bar is rated less than this, then you must not exceed that figure.

what do you plan on having in the car additional to the weight out the back? would your car be loaded as well?

the more info you give, the better the help can be.

[BLSTIC]

Oh hell no, no way I'm putting 2300kg on it, it would tear the rear end out of the car beefore I finished loading it. 200kg maybe. But it looks like the GVM of the car is around 2500kg, so that's car, plus fuel, plus four fat people, plus about 350kg split between the boot and the towbar.

I mentioned the tow capacity because there are two different tow bars available, and that may have made the difference in how much weight you can put on it. One is good for 160kg pushing down and the other is good for 230, apparently

[BLSTIC]

I hadn't planned specific items, but the car is likely to be the road trip car of the family (that or a GU Patrol, which overtakes about as well as bicycle, handles like the truck it is, and consumes fuel like it thinks it can store it for winter). We will usually have 3 people plus luggage, which fits fine in the standard car, but there have been rare occasions where we have run out of space, especially if you consider not having stuff jammed in with rear seat passengers

[prydey]

Originally Posted by BLSTIC

But it looks like the GVM of the car is around 2500kg,

unlikely. the GVM on my FG was 2240kg or thereabouts from memory.

Originally Posted by BLSTIC

I mentioned the tow capacity because there are two different tow bars available, and that may have made the difference in how much weight you can put on it. One is good for 160kg pushing down and the other is good for 230, apparently

correct. ford quote max ball weight as 10% of max tow rating.

[Blue Dog]

The tow ball weight limit is relevant for loaded trailers.
It is not relevant for hanging something off the towbar.

If you want to carry boxes or whatever behind the vehicle, buy a box trailer.
If you don't want to tow a trailer, buy a ute.

[prydey]

Originally Posted by Blue Dog

The tow ball weight limit is relevant for loaded trailers.
It is not relevant for hanging something off the towbar..

not sure how you can differentiate between the two. the weight is being added to the same area.

[jayjay99]

Originally Posted by mike_nofx

One restriction would be ball weight limit, as well as overall vehicle load carrying mass.

This is the simplest reply to your question. All you need to do is study the law of physics according to the car, truck, etc, that you own. 500 kg is max tow weight without power brakes. Doesn't mater if you have a car,truck, excettera that can pull 3 ton. Anything heavier than half a ton, must have power brakes. That's the law in South Australia. The average person on the street has no clue what ball weight limit means. Forget about ball weight limit, and just follow the limits set by the manufactures. Hi everyone, this is my first post. I hope I am here for longer than other forums have allowed me.

[Vesper Martini]

note 200 kg is like the weight of a 44gal drum, do you plan on filling the box with Bricks?

Cheaper to Buy or rent a 6x4 trailer. a special box fitted to the tow ball would cost more than the AU itself.

[commodorenutt]

Don't assume the 2300kg bar can take 230kg either.
It depends on the manufacturer of the bar, and the car.
And don't forget the de-rating for the leverage of the load being further out than the ball.

The 2300kg Hayman-Reese bar I have on my FG states 230kg on the plate.
A guy here at work has a Kia 4WD, with a 2000kg towbar, but the ball limit is a measly 100kg.

Likewise I've seen aftermarket 1600 and 1200kg towbars on the last few generations of Falcons & Commodores that are only rated to 100 or 120kg on the plate too.

[jayjay99]

All you have 2 worry about are manufactures recommendations. That way you will be covered insurance wise.

[Raptor]

Here's your best option, IMHO