Tow ball weight effectsn on tow vehicle and van

Submitted: Wednesday, May 15, 2013 at 21:15
ThreadID: 102231 Views:4663 Replies:4 FollowUps:14
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Hi all, this probably sounds like a stupid question but I am going to throw it out there anyway!
I have a caravan with a towball weight of say 200kg for example, I realise and understand that this weight must be added into the weight loading for the tow vehicle,
my question..if this weight is transfered to the tow vehicle, can that weight then be subtracted from the total weight of the van? or is this weight "counted twice"
in caculating weights of the van and tow rig?
I would love to be able to subtract the tow ball load off the van weight this would be great or am I just wishfull thinking??
I would really appreciate any comments to assist in clearing away my delema!
Thanks...Cheers Steve.
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Reply By: Member - Rosco from way back - Wednesday, May 15, 2013 at 21:30

Wednesday, May 15, 2013 at 21:30
G'day Steve

From the way I see it, you only need to consider the tow ball weight when working out how much you can carry in the vehicle i.e. it becomes a component of the weight of your total load carrying capacity.

When it comes to calculating your combined total you certainly wouldn't add it twice

Hence total combined GVM = Vehicle GVM + Van GVM - Tow ball weight (if you included it in your Vehicle GVM).
AnswerID: 511134

Follow Up By: Member - Steve O (QLD) - Wednesday, May 15, 2013 at 22:43

Wednesday, May 15, 2013 at 22:43
Thanks for your reply Rosco, my problem is I am getting close to my GCM with only a couple of hundred kg payload to play with, my reasoning was that if I have to apply the ball loading to my tow vehicle..eg part of the weight of my van is being taken by my tow vehicle..how come that weight cant be taken off the weight of the van?
am having difficulty trying to explian my thinking so I will lay out the numbers in the hope you can see where I am going with this...may be i have a large misunderstanding of this but here goes....
My GCM
allowed is 6000kg total. tare on van 2480kg weight of vehicle allowing for 2pax, full tank of juice,and ball weight of van is 3150kg
2480 +3150 =5630...leaving me 370kg before I reach my GCM, within the 3150, is 230kg ball weight....my reasoning is the tare on the van is 2480..this includes the 230kg that is being "transfered to my vehicles weight..why cant this 230kg come off the vans tare ,thus giving me an extra 230 kg to play with?
I am probably missing something here but this is the loop I seem to have got my brain locked on!!...cheers Steve.
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Follow Up By: Member - Rosco from way back - Wednesday, May 15, 2013 at 22:52

Wednesday, May 15, 2013 at 22:52
Basically I can't see any errors in your logic EXCEPT you mention van has a tare of 2480kg. Hence you need to take into consideration anything additional that you load into the van.

This is a fairly common issue where people, quite often unconsciously end up exceeding their GCM.
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Follow Up By: Member - Steve O (QLD) - Wednesday, May 15, 2013 at 23:05

Wednesday, May 15, 2013 at 23:05
Hi again Rosco..thanks for your patience..I appreciate it
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Follow Up By: Nomadic Navara - Thursday, May 16, 2013 at 23:48

Thursday, May 16, 2013 at 23:48
There is two separate things to look at. For your gross combination loading you add the weight on the front and rear axles of the tug to the weight of the vans axle group. This should not exceed the tugs GCM. If you go to a weighbridge there is no need to add anything together. You just roll the whole combination on to the bridge and the weight should not exceed the GCM.

Secondly, when you are looking at what you are towing you add the tow ball weight to the group axle weight of the van. This should not exceed the vans ATM.

If you look at things that way there should be no confusion.
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Reply By: Robert H2 - Wednesday, May 15, 2013 at 23:09

Wednesday, May 15, 2013 at 23:09
Steve,

My understanding is:-

The gross combined mass (GCM) for your tow vehicle is established from the vehicle GVM and maximum towing capacity both of which are nominated by the manufacturer.

However what is important is the following:-

The gross vehicle mass (GVM) is the measured weight of the vehicle which if towing includes the tow ball weight, everything loaded on board (including fuel) and of course the mass of you car.

The gross trailer mass (GTM) included weight of the van and everything you have loaded into it, however this figure does not include the ball weight

The aggregate total mass (ATM) is the total mass of the fully loaded caravan not hooked to the car. i.e. GTM plus tow-ball weight

The way the actual figures are established i.e. measured when you are inspected on the road (or when you take it to a weigh bridge) is by driving the vehicle and caravan onto scales that measure the axle weights for tow vehicle and caravan. The measured GVM must not exceed the manufactures nominated figure (usually quoted in the manual) and similarly the caravan must not exceed the manufactures GTM. This figure and the ATM are nominated on the compliance plates attached to the caravan chassis and can't be exceeded.

I not sure what you are trying to achieve by
"I would love to be able to subtract the tow ball load off the van weight this would be great or am I just wishfull thinking??"

Hope this helps.

Rob
AnswerID: 511138

Follow Up By: Robert H2 - Wednesday, May 15, 2013 at 23:33

Wednesday, May 15, 2013 at 23:33
Steve,
I have just read your last post and now have a better understanding of your dilemma.

You need to establish the ATM for your caravan and the GVM for your car.

Of course the caravan ATM needs to be less than the nominated towing capacity of your car.

Basically you can load your van to its ATM, and if you still have stuff you want to carry then load it into the tow vehicle until it reaches its GVM, but remember you will have to include the tow ball weight in this.

Cheers

Rob



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Follow Up By: Member - Steve O (QLD) - Thursday, May 16, 2013 at 09:23

Thursday, May 16, 2013 at 09:23
Thanks Rob, that helps think I am getting my head around it now, Cheers Steve
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Reply By: KenInPerth - Thursday, May 16, 2013 at 11:03

Thursday, May 16, 2013 at 11:03
Steve

Does this picture help - I am assuming it is still the current definition as it still seems to be used on a few sites.

http://www.caravandealer.com.au/things-to-know/weights-masses-and-payload-weights

If you know your ATM and Tare weights your max Payload is the difference between them full stop.

This takes into account unloaded ball weight (Tare (no payload weight) = tyre load + ball weight) and this is independent of being attached to the tow vehicle. I would suggest the max payload is probably a structural design constraint with safety margin.

Hope the following is correct and makes sense.

This ball weight (as part of Tare weight) is also unloaded weight - once you add payload the ball weight wil increase or decrease depending on how you distribute the load, but does not change the manufacturers limits of ATM, GTM or Payload.

I think a confusing thing about ball weight is that what is specified on or calculated from the VIN plate is an unloaded weight as determined by the manufacturer after building the caravan. Payload will change the ball weight and tyre load, but ATM and GTM must still be observed.

There seems to be no fixed specification for ball weight after loading other than the 10% rule of thumb for safe towing and not exceeding maximum ball weight for the tow bar. And I dare say the optimum ball weight would differ between tow vehicles for the same caravan. But none of this changes the manufacturer limits they specify.
AnswerID: 511159

Follow Up By: Member - Steve O (QLD) - Thursday, May 16, 2013 at 15:57

Thursday, May 16, 2013 at 15:57
Ken,this is also most helpful...looks like i will load the van & car and head off to the weighbridge to complete the picture and then make the necessary adjustments....I must be a bit thick but this can get confusing in a hurry!..Thanks again for taking the time and effort to assist..all the best Steve
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Follow Up By: KenInPerth - Thursday, May 16, 2013 at 16:22

Thursday, May 16, 2013 at 16:22
This might be of interest also as to getting a rough idea of ball weight at home

Take care and good luck - most of all enjoy your venture ...

http://caravanersforum.com/viewtopic.php?f=2&t=14461

or

http://hildstrom.com/projects/tonguescale/index.html
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Reply By: Member - Keith Berg - Thursday, May 16, 2013 at 19:32

Thursday, May 16, 2013 at 19:32
Steve,
If you have a weight distributing hitch which restores the rear of the tow the same height that it was before hitching up, then some of the tow ball weight will have been redistributed to the front wheels of the tow, with the rest being distributed to the wheels of the van. None of it will be on the rear axle of the tow.

The split will be roughly proportional to the distance between the tow ball and the front axle of the car and the mid point of the axles on the van.

If the front axle is 4 m from the tow ball and the mid point of the van axles if, say 6 metres, 40% of the tow ball weight will be distributed to the front axle and 60% to the van axles. The combined rig will of course weigh the same, but the towing vehicle will not carry all of the ball weight.

I hope this makes sense. Running each axle over a weighbridge might make it all clearer.
Keith
AnswerID: 511185

Follow Up By: Nomadic Navara - Friday, May 17, 2013 at 00:11

Friday, May 17, 2013 at 00:11
Quote - "If you have a weight distributing hitch which restores the rear of the tow the same height that it was before hitching up, then some of the tow ball weight will have been redistributed to the front wheels of the tow, with the rest being distributed to the wheels of the van. None of it will be on the rear axle of the tow."

Keith, if you have no extra weight on the rear wheels of your tug then you have tensioned your WDH bars too much. You will also have too much weight on the front wheels of your tug and are bound to have overloaded your front axle.. You should tension the bars so that the front of the vehicle comes back down to its original height or a little lower.

The weights in the table below are from a WR demo given at the Melbourne caravan show some years back and published in Caravan World. It speaks for itself.



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Follow Up By: Member - Keith Berg - Friday, May 17, 2013 at 00:26

Friday, May 17, 2013 at 00:26
Peter,
I stand corrected. With the WDH set properly the load is spread over all three sets pf axles.
My apologies.
In your example, the 220Kg tow ball weight is spread:
70kg to the rear axle
90kg to the front axle
with I suppose 60kg to the van axles
and the tow car sinks down evenly front and rear.
Sorry for the confusion and thanks for the correction.
Keith
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Follow Up By: Member - Steve O (QLD) - Friday, May 17, 2013 at 18:11

Friday, May 17, 2013 at 18:11
Rosco,PeterD,Rob,Ken & Kieth Thankyou all so very much for your thoughts and advices, it is all appreciated and has been taken on board..me thinks I got my self somewhat overwhelmed by something that is reasonably straightforward once you get you head around it!This saga all started when I decided to strip out and weigh our newly aquired van...I wanted to double check the Tare weight to make sure all was well!,anyhow that done I discovered to my abject horror that our tare was a fair bit heavier than what was stated on the van's plate, this reduced the healthy margins I thought I had down to Jenny Craig proportions!!...hence my flap & confusion..anyhow because of your advices I am seeing the light and all should be good..All the very best to you all..safe travells Regards Steve.
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Follow Up By: Member - Keith Berg - Friday, May 17, 2013 at 20:10

Friday, May 17, 2013 at 20:10
Steve,
Do check out the weight capacity of your van tyres. Many years ago I bought a very nice Millard 16 footer with bathroom. It turned out that the maximum capacity of the tyres was just equal to the unladen weight of the van. Millard replaced the tyres with ten plys free of charge and, by the way they handled it, they wanted the issue to be kept quiet.
So do make a check on the van tyres.
Keith
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Follow Up By: Member - evaredy - Saturday, May 18, 2013 at 11:23

Saturday, May 18, 2013 at 11:23
That seems to be something a lot of people don't take into account.

I know I have never given the weight v's tyres a second thought. That was until I booked my Dmax in for a suspension upgrade and a GVM upgrade. I was asked if I would be keeping the current tyres and rims or changing them.
I told them I was thinking of putting AT's on the same rims and asked why does it matter. He said that if I change tyres, they had to be rated the same as the current ones or better, if I put something less on I will not be legal.
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Follow Up By: Member - Steve O (QLD) - Saturday, May 18, 2013 at 17:14

Saturday, May 18, 2013 at 17:14
Yes thanks Kieth and Evaredy, that is one I was already across, the van is a tandem, I had the old rock& rolla sus with beam axles taken off anf replaced by Vehicle Components with a Cruisemaster independent suspension with air bag suspension, the tyres are LT off road tyres rated at 1100kg capacity each, I luckily had the vans gvm uprated at the same time, the engineer doing the certification also advised that with indepentent suspension your tyres must be rated at20% more load carring capacity as the suspension is not load sharing...something to keep in the back of the mind for those with independant tandem suspensions ..Cheers Steve.
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