Tow Ball weight

Submitted: Monday, Feb 25, 2013 at 21:48
ThreadID: 100762 Views:2131 Replies:4 FollowUps:12
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Weighing up choice of two interior designs which impact on Tow Ball weight for new van. Is there any significant advantages/disadvantages to heavier/lighter tow ball weight when deciding which design to choose? Our preference is for the design which would mean heavier tow ball weight. The length of the van would be the same.

Cheers all.
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Reply By: Olsen's 4WD Tours and Training - Monday, Feb 25, 2013 at 22:16

Monday, Feb 25, 2013 at 22:16
Tow ball downforce is a design criterion of each individual van that counteracts the aerodynamic and other forces that would otherwise destabilise the combination at speed.

If not specified, it can be calculated by deducting GTM from ATM.

When considering Towball downforce, once should consult the load limitations for the towing vehicle. eg. does the additional tow ball weight significantly reduce the load carrying capacity. For some designs tow ball weight is not equal to kg per kg to load in the load space.

Additionally one should consider the specified towball downforce limit for the towing vehicle and tow bar and load levelling devices if intended to be fitted.

AnswerID: 505566

Reply By: Ross M - Monday, Feb 25, 2013 at 23:01

Monday, Feb 25, 2013 at 23:01
Arsenal Phill

If I had a choice I would choose the lighter towball weight.
While I understand there is a common belief the ball weight should be 10% of the van, if it is a big van the weight on the ball is very large.
The weight does however, have to be sufficient to give additional control and side ways traction on the rear wheels of the towing vehicle. Usually large amounts also make the front of the tug to rise too much and the rear to sink too much.
The use of towing aids is then required as it often is, but with large towball weights the hitch has to be very large and is handling considerable forces.
To have this all in balance is the juggle most go through, while many have far too much ball weight in the belief it is the feature ensuring stability. While some is necessary many are too much.
Towing stability is as much about the vehicle, it's shock absorbers ability and it's spring rated and load carrying ability as it is with ball weight. Dynamic ability is the true test of what is correct.
Most vehicles do not have suitable shock absorbers to be able to cater for the additional forces and mass transfer of weight distributing hitches. Upgrades of shocks would be the most important item on my list. Without the control good suitable shocks provide an emergency situation is often called an accident.
A lot of people are happy with their setup but don't know how close to the wind they are sailing because they haven't had that "revealing emergency" happen to them, some have.

To me lighter and suitable is safer.

Ross M
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Follow Up By: Nomadic Navara - Tuesday, Feb 26, 2013 at 00:50

Tuesday, Feb 26, 2013 at 00:50
Quote "Most vehicles do not have suitable shock absorbers to be able to cater for the additional forces and mass transfer of weight distributing hitches. Upgrades of shocks would be the most important item on my list. Without the control good suitable shocks provide an emergency situation is often called an accident."

Ross, where did you glean that little gem from. Can you please supply me the links so I too can be educated.
PeterD
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Follow Up By: ozjohn0 - Tuesday, Feb 26, 2013 at 10:01

Tuesday, Feb 26, 2013 at 10:01
Ross,
Light ball weights on long heavy vans spells disaster in the making.
While 10% has been the accepted level for may years research and testing has show that it is indeed a good starting point, but longer heavier vans may require even heavier ball weights up to 15% to maintain stability.
I suggest you read articles by Colin Rivers (Google) for more information.
Ozjohn.
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Follow Up By: Ross M - Tuesday, Feb 26, 2013 at 14:15

Tuesday, Feb 26, 2013 at 14:15
Nomadic Navara
The shock absorbers on most vehicles are usually only sufficient for the mass control of the vehicle mass and unsprung weight.

By adding a van to the equation the amount of mass to be controlled on side sway and porpoising is far greater and no OE shocks are really up to the task.
Not sure what you are on about with the "show me the links" comment.
Why does there have to be a link to something before anyone thinks a comment is valid. Having had a lot to do with shock absorbers and their operation, shockers should be matched to a situation, adding a van alters the situation quite considerably, but as usual no one really cares about it or even considers the situation to be different, possibly because it never enters their heads and isn't the normal issues talked about. Poor/unsuitable shock absorbers cause more accidents than people realize.
Monroe company has the Motto "Don't discover your shocks are worn by accident"
Most Japanese based vehicles like Navara, Dmax, Colorado are fitted with shocks only good enough to sell it but not for the work it is designed to do. Most do not dampen at all well after 30,000km and that is for the vehicles weight only, no extra.

ozjohn0
I haven't mentioned having the ball weight insufficient for stability just don't have too much.
The tow vehicle characteristics ie suitable suspension, body roll control, matched shockers, appropriate tyres sizes and inflation and the distance from drive axle to towball, all play a huge part in inherent stability. Unfortunately people think it is all to do with the caravan.

Ross M
A grade Automotive Engineer
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Follow Up By: Dennis Ellery - Tuesday, Feb 26, 2013 at 15:14

Tuesday, Feb 26, 2013 at 15:14
Ross – you’ve suddenly become an engineer.
You previously described yourself as a technician.
Have you just been accepted by The Institute?
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Follow Up By: Ross M - Tuesday, Feb 26, 2013 at 17:09

Tuesday, Feb 26, 2013 at 17:09
Dennis Ellery
I can list it all but I thought I would put it into perspective for electrical engineers.
Listing credentials doesn't improve the road handling of a tug and caravan but suitable loading, suspension, and shockers fit for purpose sure do.
PS I'm not describing myself at all. Accredited Automotive organisations do that.
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Follow Up By: Dennis Ellery - Wednesday, Feb 27, 2013 at 14:26

Wednesday, Feb 27, 2013 at 14:26
Hi Ross,
I know you didn’t mean degree qualified engineer but rather a title awarded by an automotive organisation.
It’s pointless listing your engineering qualifications as they mean different things to different people.
Old steam engine drivers and some mechanical and automotive tradesmen call themselves engineers.
When I was working, I used to hire out engineers to consulting engineering companies and government departments.
I came across a lot of self-titled engineers who lacked the qualifications that would entitle them to be classed as engineers by our clients.
The clients required engineering degrees issued by recognised universities, or eligibility for membership of the Australian Institute of Engineers
Dennis Ellery
Aeronautical Engineer, Electrical Engineer, Mechanical Engineer, Structural Engineer, Doctor of Bulldust and too many more to mention LOL.
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Follow Up By: Ross M - Wednesday, Feb 27, 2013 at 20:00

Wednesday, Feb 27, 2013 at 20:00
What has all that got to do with towing a caravan and having a safe vehicle to tow it with?
It sounds like you have been a theoretical desk jockey and not someone who has necessarily had experience with anything mechanical.
I am confident I could diagnose your vehicle and you seem to not value the people who can diagnose and repair your vehicle.
I have seem this before.

Qualifications are just one aspect of life, experience and ability to apply it is another.
I know my capabilities and don't care if you feel the need to continually dispute issues with others.
Oh, how are your shock absorbers going, do you really know if they are ready for the all important emergency you may face on the road even at 80 or 85km/h while towing the van. If you value your life and your wife, it might be best to know if they are suitable for purpose or not. Comment based on experience not qualifications.

Good luck and all the best in your future motoring.

Ross M
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Follow Up By: Dennis Ellery - Wednesday, Feb 27, 2013 at 20:39

Wednesday, Feb 27, 2013 at 20:39
Hi Ross,
I didn’t mean to denigrate your experience.
My mechanic says I have two stuffed rear shock absorbers on my Troopy.
What would you suggest as a replacement – towing a 3 tonne van with a towbar ball weight of around 200kg – mostly for highway towing?
Regards Dennis
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Follow Up By: Ross M - Wednesday, Feb 27, 2013 at 21:30

Wednesday, Feb 27, 2013 at 21:30
Is is a sad situation when you "come the bounce" with people who are trying to tell you something.
I feel sorry for you if you can't tell your shock absorbers are stuffed and need a mechanic to do it for you.
If they are stuffed, you would have been able to feel the progressive degradation of the performance over time and change them. Any undulating road will tell you.
There are very few shock absorbers which have a lasting performance past 50,000km. I changed three sets of ARB OME shocks on my 60 series in 150,000km. They don't last at all well, poor product for the money.
The ability to steer, brake and control the additional caravan mass, which is trying to tell the tug what to do, is of paramount importance.

If I drove your vehicle on an average road I will tell you within 1/2 a km if they are ok or not.
Unless the shocks are of well recognized quality they will be unsuitable for purpose long before the tyres are worn out.
Go with a Good brand not necessarily a popular brand.

Ross M
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FollowupID: 782654

Follow Up By: Dennis Ellery - Thursday, Feb 28, 2013 at 12:17

Thursday, Feb 28, 2013 at 12:17
The shocks are original – done 85,000ks.
The ride feels ok but the mechanic noticed fluid on the outside of the shockies at the last service.
I will take his advice that they are on the way out.
Thanks for the info
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Reply By: Nomadic Navara - Tuesday, Feb 26, 2013 at 00:48

Tuesday, Feb 26, 2013 at 00:48
You are a little light on details. What is the difference in designs? Also is one a European style? European style vans can get away with lighter ball weights.

The bigger the van the heavier the ball weight that is needed. The Americans use 15 - 25% ball weights on their vans. Read this link to see the results of not having enough ball weight.

What is the layout of the two vans and what are their ball weights? Remember the ball weights stamped on the compliance plates are the empty ball weights. They will alter considerably when you load them. All the vans I have had tend to have heavier ball weights after loading.

Also are you looking at a large van with a front or rear end kitchen? If so read these papers.

Vehicle Dynamics - University of Bath caravan studies

If you read and fully understand those two papers you will not look at front or rear kitchen vans. Also you will not install jerry cans, extra spare tyres, generators or toolboxes on the ends of vans.
PeterD
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Follow Up By: Member - Arsenal Phill - Tuesday, Feb 26, 2013 at 09:29

Tuesday, Feb 26, 2013 at 09:29
Hi NN

Thanks for the input. Basically the two vans are the same. Both size and manufacturer. The difference on the two models is the position of the door, and an angled interior kitchen bench. Other than that all interior equipment is the same along with the fittings.
Our preference is for the angled bench design but in order to have this, they move the door, hence the difference in ball weight as it alters the postion of the axles on the chasis I presumme.

Cheers
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Follow Up By: Dennis Ellery - Tuesday, Feb 26, 2013 at 13:05

Tuesday, Feb 26, 2013 at 13:05
High Peter - those are interesting studies.
It shows, amongst other things, that those large vans with centrally located wheels are inherently unstable.
Stability increases with high tyre pressures, heavy tow ball weights, centrally located loads and slow speeds.
I have such a van and travel between 80 to 90 ks an hour – much to the annoyance of others.
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Reply By: Member - Bruce C (NSW) - Tuesday, Feb 26, 2013 at 09:21

Tuesday, Feb 26, 2013 at 09:21
Hi Phil,
In answer to your specific question I would say that lighter is better, however the industry aims for that 10% rule and for very good reasons.

While the 10% of van weight on the coupling is a rule of thumb, it can be varied a couple of percent either way, and usually ends up that way in the loading of the van, it never the less important to keep close to that 10% of van weight on the coupling.

It provides the stability in the towing process which I imagine has been discovered by years of experience by the industry. Otherwise it would not have become the universal rule of thumb that it is, I guess.

The ball weight is deducted from the carrying capacity of the tow vehicle as once hooked up it becomes an integral part of the tow vehicle load. This means less carrying capacity within the vehicle in order to maintain stability while towing.

Weight distibution hitches merely balance this extra ball load throughout the tow vehicle and van so as not to place it all on the back axle of the tow vehicle. Thereby adding to the stability of the outfit.

Cheers, Bruce.
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restless and lost on a track that I know. HL.

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