Towball Weight - Just wondering !

iana · Guru

Towball Weight - Just wondering !

Whenarewethere · Guru

All on computer years before the first component is made.

Over 30 years ago I was in the aluminium industry & computers were calculating this stuff, but slower!

erad · Guru

Brilliant idea, Iana, but that is far too complicated for a caravan manufacturer to even begin to think about. When I bought our caravan, it was built by the leading van manufacturer in Oz to a special order. I wanted a shorter drawbar so the van would fit in my shed. I asked for 150 mm shorter, but they said that they could only do 200 mm shorter. Good, I said. The van was duly delivered and the towball weight is so heavy that there is no way I can lift it myself. Now, a 200 mm shorter drawbar should not make a great difference, but there is something which is awfully heavy there. Mind you, it makes the rig tow very well - heavy ball load, shorter drawbar - it is very stable.

In addition to the shorter drawbar, we also ordered an air conditioner. This was put in the front corner. I am sure that the Tare, ATM and GVM of the caravan as shown on the plate are nothing like what I have. They are way under what things really are. (And of course, WE don't load too much stuff in the van - Ha!)

-- Edited by erad on Sunday 22nd of March 2020 09:15:44 PM

woofta and precious · Senior Member

I'm pretty sure some of you guys are on some good drugs! Just let me know which ones!!

Iva Biggen · Senior Member

iana wrote:
As I was checking tyre pressures, and as I kicked the last tyre, I wondered how the manufacturer worked out tow ball weight. My thoughts were that since the suspension on our van is a separate assembly, it would make sense, that this assembly remained free to move until construction had finished, then the van is weighed, and tow ball weight calculated, you know the famous 10%.
Now all the manufacturer has to do is sit the jockey wheel on a separate surface, and then move the suspension one way or the other, until the van weight minus the calculated tow ball weight is read. With so many variants of design, does anyone know if this is how it is done.

That method would be quite difficult with a caravan as the position of the wheels in relation to the floor plan all has to fit together.

Having said that, it is a different story with boat trailers.

These trailer are generally made to fit a variety of boat styles with the only real requirement being the correct length for the vessel it is to carry.

If you buy a new trailer a good manufacturer will ask you to bring your boat in and then through the design of the suspension being adjustable, they will move the axle assembly to achieve the correct balance onto the tow hitch.

It would be good if caravans could be set up in that manner

Radar · Guru

Iva Biggen wrote:
iana wrote:
As I was checking tyre pressures, and as I kicked the last tyre, I wondered how the manufacturer worked out tow ball weight. My thoughts were that since the suspension on our van is a separate assembly, it would make sense, that this assembly remained free to move until construction had finished, then the van is weighed, and tow ball weight calculated, you know the famous 10%.
Now all the manufacturer has to do is sit the jockey wheel on a separate surface, and then move the suspension one way or the other, until the van weight minus the calculated tow ball weight is read. With so many variants of design, does anyone know if this is how it is done.

I would say this is a big No.

Most manufacturers would not have a weighbridge at hand.

I stand there an look at my caravan, there is no way that would, could happen with the build process. Like where do we put the frig after its finished,

Maybe this is how they come by Expanda style caravans when they realized the bed was standing against the wall.

Or others think they are lucky and got a pantry or a useless cupboard.

The mind boggles.

Realistically both my caravans tare weights, towball weights were very close to the vin plate. Both caravan manufactures are still in the game, our 2012 mid budget manufacture is going a head quite well and reading on our FB site most are very happy with the end product including the vin plate weights, some have asked for more kgs on their gross mass.

yobarr · Guru

This is a photo of a caravan that I believe was custom-built in Melbourne for a family from South Australia.Despite warnings about low towball weights,the buyer insisted on this design,with most weight being to the rear of the axles,and the van allegedly having a very low ball weight. On their return trip to South Australia,after picking up the van,the family was overtaking,or was overtaken,on a straight section of road,by a semi-trailer.The turbulence created by the semi-trailer caused the van to start swaying,with the car and van eventually leaving the road and the car overturning. Sadly,all family members in the car died. You should not mess about with towball weights,with 10% of ATM being the generally accepted figure if safety is of ANY concern.More important though,is that the weight on the wheels of the car should be at least 10% more than the weight on the van's axle group.I understand that Collyn Rivers,a noted authority on weights and dynamics,with over 60 years experience, suggests that the weight on the car's wheels should be 20% more than the weight on the van's wheels.Cheers

-- Edited by yobarr on Monday 23rd of March 2020 11:36:33 AM

Greg 1 · Guru

That is a prime example, yobarr, of a van that should never have been built. The positioning of the axles so far forwards is a moral for the thing to sway. Strongest word in the english language is also one of the shortest, that is NO. The manufacturer should have walked away from that one. Anyone worth there salt making vans should know that is a bad idea and likely to end in tears.

boab · Senior Member

exactly Greg the van has control of the tug with such a short distance from tow ball to axles for all we know it had 10% tow ball weight which would of been very little use to stabilize the van its a prime example of the tail wagging to dog

Hylife · Guru

Modern caravan manufacture requires full engineering drawings and specs during the design phase to cover the manufacturer against legal liability should something go horribly wrong resulting in an accident being attributed to poor design.
To this end, most automotive design these days uses CAD CAM software such as the popular "SolidWorks"
(CAD CAM = Computer Aided Design Computer Aided Manufacture).
This software has absolutely every spec imaginable entered into it regarding the materials that will be used.
When the customer makes variations to the original van for their order, these changes are entered into the CAD CAM software which then recalculates all the related details of the design.
The CAD CAM software recalculates the revised chassis and cabinetry designs and that gets sent off to the cabinetmaker and chassis manufacturer (eg, G&S Chassis etc).
Internal layout changes, construction material changes, suspension changes, drawbar changes, that extra Gerry Can holder, different wheel designs, even a different fridge or sink, everything is entered into the software for a caravan chassis layout, design and cutting list.

yobarr · Guru

Greg 1 wrote:
That is a prime example, yobarr, of a van that should never have been built. The positioning of the axles so far forwards is a moral for the thing to sway. Strongest word in the english language is also one of the shortest, that is NO. The manufacturer should have walked away from that one. Anyone worth there salt making vans should know that is a bad idea and likely to end in tears.

Exactly right Greg....and it would have been even worse if the manufacturer hadnt flatly refused to put the AC at the rear of the van,over the bedroom,as the buyer had asked.Van builders now are flat-out keeping up with demand,but this may not have been the case in 2004-2005,so they may have been happy to build whatever was ordered? Cheers

Cupie · Guru

yobarr wrote:
This is a photo of a caravan that I believe was custom-built in Melbourne for a family from South Australia.Despite warnings about low towball weights,the buyer insisted on this design,with most weight being to the rear of the axles,and the van allegedly having a very low ball weight. On their return trip to South Australia,after picking up the van,the family was overtaking,or was overtaken,on a straight section of road,by a semi-trailer.The turbulence created by the semi-trailer caused the van to start swaying,with the car and van eventually leaving the road and the car overturning. Sadly,all family members in the car died. You should not mess about with towball weights,with 10% of ATM being the generally accepted figure if safety is of ANY concern.More important though,is that the weight on the wheels of the car should be at least 10% more than the weight on the van's axle group.I understand that Collyn Rivers,a noted authority on weights and dynamics,with over 60 years experience, suggests that the weight on the car's wheels should be 20% more than the weight on the van's wheels.Cheers

-- Edited by yobarr on Monday 23rd of March 2020 11:36:33 AM

Chris ..

That would have to be the case of Jong wouldn't it.

I have attached the full Coroner's findings.

yobarr · Guru

Hi Cupie....I dont seem to be able open this on my iPad,but the name certainly is familiar.If my memory serves me correctly,the family involved was of German descent,and included a young lady and her middle aged parents. If/when I find out how to open the link,I certainly will again read the report.Many years ago I did read it,but I dont seem to be able to find it now.Cheers

Yay...sorted! Although the coroner was unable to make a judgement about ball weight,the photo showing the van sitting level,with no jockey wheel, surely is self-explanatory? Seems the van had separated from the car,and had then travelled quite some distance with no sign that the drawbar ever touched the ground? Spare me.

-- Edited by yobarr on Tuesday 24th of March 2020 12:13:19 PM

montie · Guru

It's all very simple guys.
When the van is completed at the factory it is weighed and this measured weight is stamped on the compliance plate and includes all factory fitted options. That is the factory Tare weight.
The ball download weight is then measured. The difference is the calculated GTM.

It needs to be noted that there is no legal requirement for a van manufacturer to stamp anything other than the rated ATM on the compliance plate regarding weights.