Buying a Caravan Feedback

Is it thus correct to calculate Tow Ball Mass as:

ATM less GTM ?

Yep,

Just remember that the recommended tow ball mas is about 10% of the ATM.

This gives a better balanced van and makes towing a much more pleasant experience.

And always remember it is illegal to tow a van that has a higher ATM than the vehicle towing it is rated for.
This applies whether or not the van is fully loaded. If the ATM plate on the van is more than your cars rated capacity its illegal.
I found out the hard way and it cost me another $23,000 for a new vehicle that could tow the van legally.
If its a single axle van a bit more than 10% ball weight will make it tow better. My tandem has 14% and tows like a dream.

On rereading your post the 400kg would apply to a tandem axle van. Most single axles have a maximum of 300 kg or less.
Also check the tyres for carrying capacity.
Can make a difference as to how much of a load it will carry.

I have just gone through getting my Roadstar recertified to carry and extra 150kg and its quite complicated and lots get taken into account.
Eg size of brakes Rating of tyres, hubs and bearings and rims. Thickness of chassis wall, depth of chassis and how far back it goes at that size.
Capacity of springs, capacity of chassis as a whole.
Plus the cost of about $500 to do it.

HI Graham,

Thats an interesting comment about % ball weight - the higher the % the better.
Our ATM is 2700 Kg and GTM is 2550 Kg meaning ball weight is 150 kg.
AS a % of ATM its only 5.5%.
But it tows beautifully - its a modern style van with tandem axles towards the rear - both past the centre of the van. I don't know if this helps handling or not.
Any thoughts,
Cheers
Glen

The 10% is only a guide but if you load too much on the ball the van will be unstable as it will be if you load too little. A dual axle van will generally have a bit less % on the ball than a single.

Geepeem
When you say your ATM is 2700kg is that a weight over a weigh bridge, or is that simply the figure provided by your van manufacturer as the maximum allowable? And similarly is your 2550 GTM an actual figure or the figure supplied by the manufacturer.
I take your point about the van towing beautifully, but I think you would be better off taking it to a van service centre to have your ball weight measured, 5.5% sounds awfully low to me. Have you read this Coroner's report:Site Link
The crash involved a caravan which it was suggested had a very low or zero ball weight.

tessa

I cant get that link to work, try this:
http://www.courts.sa.gov.au/courts/coroner/findings/findings_2006/jong.finding.htm
tessa

Hi Tessa,
Both weights are on manufacturers plate on chassis.
But after reading this I probably should get it weighted as I don't know if the extras are inluded:
Eg solar panels on roof, rear dual tyre rack with 2 jerry cans, 2 nine kg gas bottles, air con, automatic hydraulic stabiliser leg sytem.

I suspect all these were added after manufacturer (I bought van second hand).

Cheers,
Glen

Tessa

When you copied the link address from your browser and posted it in followup 7 you copied too much. The "insert Link" box adds http:// to the front of what you paste into the box. In doing so it produced an address of http://http//www.courts.sa.gov.au/courts/coroner/findings/findings_2006/jong.finding.htm for you. Next time you copy an address leave out the http:// bit on the front.

PeterD

Thanks Peter

tessa

Thanks tessa for that reference to the SA Coronial Inquiry into that caravan accident where unfortunately 3 people died.
I read through it all last night. It is very interesting.
Although no explicit findings came out I'm convinced the low ball weight (or even nil ball weight) was a factor in the accident.
I am confident I have a significant ball weight in mine (regardless of whether its calculated as ATM less GTM.
To wind up jockey wheel I need to use both hands - there is a lot of weight on it. And also when on Landcruiser (with extra heavy rear springs) it lowers towbar by 7cm.
As I stated with both axles towards the rear (and past the centreline) there is a lot of weight on the towball. But it does tow well and tracks straight behind tow vehicle.
But I haven't yet had the experience of being passed by a B-Double at speed so this "yaw" issue is something to consider and be aware of.
Thanks again for posting that inquiry - it should be compulsory reading for all new caravaners as to what can happen in adverse circumstances.
Cheers,
Glen

some WD40 on the screw in the jockey wheel might help cos mine with 315 can be wound with one hand quite OK
Hopefully you are using a WDH to re level the cruiser.
Mine comes back up with the WDH and it only has standard springs at the moment. Am putting progressive ones in shortly.
If you reckon you have only 150 kg on it two people should be able to lift it no trouble. Can they ????????.
Weight distribution also plays a large part in problems with etc.. Also the design of the van can as well, as highlighted in the link.
Some models are all plated the same but then people get alterations done which can upset the dynamics of the van and alter the handling quite dramatically.
All these things need to be watched for especially when buying a second hand van.
You see vans with extra bumpers on the back with jerry cans and bike racks and even a bl**dy great toolbox.
Do these people ever stop to consider what they are actually doing and the consequences of it.
I really wonder sometimes.

NO Graham there is no way 2 people could lift my drawbar on to the tow ball.
The 150kg is simply the calculation as described above - but in my case I think its wrong.
My maximum tow ball weight is 350kg but I don't think its that heavy.
I'll try the WD40 on the screw that will no doubt help.
I don't have a WDH yet but will get one in due course. So far we have only used the van for short distance local holidays - no long distance yet.
Thanks for the comments - appreciated.
Cheers,
Glen

At the end of the day, the only way to really tell what you van actually weighs is to run it over a weighbridge and check the weight of the van only whilst it is sitting on the trucks towball. Then take the weight on the jockey wheel and move the truck then lower the jockey till it is around the height it was when on the trucks towball then have it weighed again.

The last figure is your ATM, the first is your GTM and take your GTM from the ATM and you'll get the ball load. If any of these figures are too far from your plate figures then you need to do something, Either take out the rock collection or rebalance your van.

Everyone should ask for a current weighbridge certificate before they buy the van. I would even go to the stage of watching as it was weighed. .as most vans are way out from the plated figures and the attitude of some dealers is less than altruistic.

Exactly what I said if you read down further


To Greenpeem The best thing you could do is buy a WDH. If nothing else it will stop your headlights pointing to the sky when towing van. You will notice the difference and they should be compulsory I reckon.

There is a local here who tows a 24 ft Coromal without one and his front wheels are just about off the ground when its hooked up. Ignorance is bliss I guess and stupidity is rife.(in his case)

That is sort of true and ball weight can be manipulated by the way u load the van.
I had to fully load my van before recertification as if we had everything we would take on a trip.
What I did was weigh everything on our list and then load the van with the correct weight by using water cans and my spare wheels of the tow car.
Original plate ATM 2564 New plate ATM 2800
Ball weight 315.
This was the Maximum that the chassis, tyres rims etc would allow so it all worked out OK Any more and I would have been in for expensive modifications.
As in any trailer it is advisable to load it "ON" that is more weight on the front than the back. Even a 6x4 trailer is better like that
. Best way to check ball weight if you havent got the proper scales is to go to the weighbridge and weigh the whole van with jockey wheel down and uncoupled from car. Get that weight. "A" Move it backward and rest only the jockey wheel on bridge Thats your ball weight."B" Then run it forward until jockey wheel is off the bridge and see what you get. Really should be the difference "C: of A less B but not always apparently.

Also its hard to tell what your real Tare or empty weight is apart from whats on the plate as some weigh it DRY empty which can have empty gas bottles on it or not. Batteries or not. Air con or not depending on what is "standard" configuration. In my case with 2 batteries 2 solar panels and air con it was 2.300 when it was plated at 2164
First thing hopefully before buying is WEIGH IT for $20 bucks its well worth it
Wish I had instead of listening to salesman who said " Just dont fill the water Tanks She'll be right" Ha ha

ATM and GTM are only limits as to how heavy your van can be. They are stipulated by the manufacturer. These weights are not variable. You may have them altered by a qualified engineer if he certifies that the construction of the van can take it or if you have had the van upgraded.

The ball weight will only ever equal to the ATM minus the GTM if you can load it to the manufacturers (or subsequently amended) maximum permitted loading. To find the actual ball weight of your van when loaded you either have to get someone to weigh it with ball weight scales (used to be available from Hayman Reese) or take it to a weigh bridge as Graham suggested.

When I weigh my van I take it to the local weigh bridge. I remove the WDH before driving over the bridge, making sure the wheels of the tug are clear of the bridge. I have a reading taken of the group axle weight first. I then lower the jockey wheel, raise the coupling from the ball and check that safety chains still swing freely (I don't disconnect them, but check that they don't effect the readings.) I then request that they weigh the total weight of the van. I then subtract the group axle weight from the total eight of the van to obtain the ball weight. You will note I have not used the terms ATM or GTM in this paragraph (up until now,) when I weigh my van I hope that the two figures I am given are less than the ATM or GTM. If they are not I do something about it. A couple of years ago I spent a few grand replacing the axle with one of greater carrying capacity and having the van re-certified so that I could take what the boss has determined we need and also because the van weighed a couple of hundred kilograms more than ti tare weight stated on the compliance plate and registration papers.

PeterD

In regard to your method of weighing isnt that what I just posted basically except I did the ball weight on its own as well. I also got the ball weight done with a set of Hayman Reece scales whilst it was being recertified.
The figures as you say probably wont be the same as on your plate cos I would say that well in excess of 50% of vans would be overloaded.
Then you have the tow car loaded to the hilt with a tinny on top and its tyres bulging from the weight.
Doesnt anyone consider the CGVM as its there to be adhered to.
Might be fine till an accident as posted above and the investigator decides to weigh everything.
I have been told from within the industry that this is being done in almost evey accident case now even to the extent of making the people in the vehicle at the time sit in it whilst it gets weighed.
Something to be thought about before embarking on a trip.
Has cost me quite a bit to be legal but at least one less thing to be worried about later.

Graham

"In regard to your method of weighing isnt that what I just posted basically except I did"

I was not commenting on whether you were correct or not in your way of measuring even though you did more measurements to get the same result. What I was doing was backing up lifeisgood (wish people would use a personal name as well as their member name.) I was just repeating the simple method of ball weight measurement in an effort to convince people they should not use the terms ATM and GTM for the weights of the van as measured on a given day. Your van weights will vary a little from trip to trip but your vans ATM and GTM will always stay the same no matter how you load it.

PeterD

Fair enuf just thought u might not have read my post.
I always took ATM as what it is The whole weight of everything whether or not it equals your plated weight.
I took my van to an engineer who referred to altering the ATM in variance of the plated weight.
I understand what you are saying but to call it somehing else, I think would confuse the issue even more as a lot of people dont understand the usage as it is.
I would differ in that the ATM or GVM if u like on the day is what it weighs as is the GTM.
Whats on the plate is what it legally shoud be.
Whether it is or not is why you are takling it to the weighbridge.

On my weighbridge certificate it is referred to as Gross Mass but as it usually is used to weigh an empty and then a full truck I guess they use that terminology.
I got my ball weight by using a Hayman Reece scale.
Last time I used GVM I got shot down so where do you go???