D-MAX Tow Ball Download calculation

KevinJ · Senior Member

D-MAX Tow Ball Download calculation

yobarr · Guru

KevinJ wrote:
Can I get some clarification on Tow Ball Download calculations please. I was under the impression that TBD was a percentage of GTM, not ATM.
The attached file is a screenshot from the ISUZU web site:
https://xnet.iua.net.au/sites/default/files/marketing/attachment/MOP1674_IUA_2018%20D-MAX%20PAYLOAD%20CALCULATOR_FIELD%20FORM_0.pdf

Hi Kevin....the generally accepted towball download,or towball weight,is 10% of ATM.However,you are now likely to get many different opinions and stories. Somewhere I read that,depending on the relative sizes of the van and the car,that figure can vary from 8% to 14%? However,if safety is of any concern,always the weight on the cars wheels should be at least 10% greater than the weight on the vans wheels. The Isuzu chart is correct,but if safety is of any concern,that car cannot tow 3500kg.If you were indeed silly enough to hook up to a 3500kg van,with 10% towball weight,the weight on the wheels of the van (3150kg) would be more than 10% greater than the weight on the cars wheels(2850kg) you would be an accident looking for a place to happen Cheers

-- Edited by yobarr on Tuesday 10th of September 2019 04:58:59 PM

KevinJ · Senior Member

Thanks Yobarr,

You can see my confusion. This web site days TBD is typically 10-15% of GTM - See screenshot below

https://www.carsguide.com.au/tradies/advice/vehicle-weights-explained-tare-kerb-gvm-payload-and-trailer-figures-73041

This web site days TBD is typically 10-15% of ATM

http://rview.com.au/wp-content/uploads/2015/05/RView-WEIGHTS-1.jpg

I'll go with your advice on this and ignore Mr Google.

yobarr · Guru

KevinJ wrote:
Thanks Yobarr,
You can see my confusion. This web site days TBD is typically 10-15% of GTM - See screenshot below
https://www.carsguide.com.au/tradies/advice/vehicle-weights-explained-tare-kerb-gvm-payload-and-trailer-figures-73041
This web site days TBD is typically 10-15% of ATM
http://rview.com.au/wp-content/uploads/2015/05/RView-WEIGHTS-1.jpg
I'll go with your advice on this and ignore Mr Google.

The problem may be that many people,even journalists and people in the industry,do not know what the various acronyms mean? And whilst some people are aware of what the acronyms mean,there is apparently little understanding of their relationship to one another? Stick with 10% of ATM and you will be alright.You might like to PM me with details of your car and van so I can help,as,in many cases,it is very easy to exceed your cars rear axle capacity.Cheers

-- Edited by yobarr on Tuesday 10th of September 2019 07:10:45 PM

KevinJ · Senior Member

Thanks Yobarr,

i have neither car nor van yet. I am researching everything so when I am ready to retire in 12 months or so, I will have all the info I need. I am however leaning towards either the DMAX or Mux with a 20 foot Alan Graham Outlander.

My previous van was a Jaco Swan camper van which was perfect with kids, but not for our next adventure.

yobarr · Guru

KevinJ wrote:
Thanks Yobarr,
i have neither car nor van yet. I am researching everything so when I am ready to retire in 12 months or so, I will have all the info I need. I am however leaning towards either the DMAX or Mux with a 20 foot Alan Graham Outlander.
My previous van was a Jaco Swan camper van which was perfect with kids, but not for our next adventure.

Hi Kevin....Be aware that the Mux is a much lighter vehicle than is the DMax,and has a much shorter wheelbase.The shorter the wheelbase,the more unstable is the car when a trailer is hooked up....tail wagging the dog.And it is much easier to overload the rear axle on the car.Please feel free to contact me if you think that I can help you,and good luck with your research!Cheers

-- Edited by yobarr on Tuesday 10th of September 2019 07:45:07 PM

KevinJ · Senior Member

Thanks Yobarr,

i have no doubt there will be more questions as I research more.

montie · Guru

I'm not sure I quite understand this discussion.

The towball download rating for the Isuzu DMax is 350kg maximum. Measured ball weight at the coupling cannot legally exceed this rating. This rating is set by the tug manufacturer, Isuzu in this instance. How Isuzu arrive at this rating is irrelevant, it is set at their discretion.

As a rule of thumb measured ball weight is considered to be ideal at around 10% of the van's loaded weight regardless of the rating.

Ball weight is not calculated it is measured.....ball rating is a set limit not to be exceeded by the measured weight.

The measured ball download at the coupling must not legally exceed the lesser of the following:

1) The tug manufacturer's rating. (In this case 350kg)

2) The towbar rating

4) The van rating if there is one.

-- Edited by montie on Tuesday 10th of September 2019 09:37:14 PM

dabbler · Guru

^^^^^^^^^°^^^^^^ Wot Montie sed. It's meaningless to discuss TBM without knowing the tow vehicle and it's legal max.

KevinJ · Senior Member

Thanks Montie,

I understand all that. My confusion was over one website (ISUZU saying TBD = ATM * 10%) whereas another website said TBD = GTM * 10%.

I also understand this is just a theoretical 10%

yobarr · Guru

dabbler wrote:
^^^^^^^^^°^^^^^^ Wot Montie sed. It's meaningless to discuss TBM without knowing the tow vehicle and it's legal max.

Did you not notice that the OP submitted a chart from ISUZU,and discussed the possible purchase of a DMax or an MUX? My posts were made with the DMax as the subject vehicle,and weights were discussed.I also mentioned the shortcomings of the MUX......Cheers.

-- Edited by yobarr on Wednesday 11th of September 2019 08:29:53 AM

Dougwe · Chief one feather

KevinJ · Senior Member

Now that I don't trust websites for GTMs, ATMs etc, can I get confirmed that GCM = GVM + GTM and not GCM = GVM + ATM

montie · Guru

KevinJ wrote:
Now that I don't trust websites for GTMs, ATMs etc, can I get confirmed that GCM = GVM + GTM and not GCM = GVM + ATM

GCM=GVM+GTM

GTM = ATM - Ball Weight.

KevinJ · Senior Member

Thanks Montie,

I appreciate the prompt reply.

Tones · Veteran Member

Hi Kevin,

As a side issue and in view of the fact that you have mentioned both Dmax and MUX in your considerations, please be aware also of the different ratings for both of those vehicles. The Dmax is rated to tow 3500KG with 350 TBW maximum whilst the MUX is limited to 3000Kg and 300TBW maximum.

The other major difference is that the Dmax has rear leaf spring suspension and the MUX has coils. Hope this helps.

Tones

KevinJ · Senior Member

Thanks Tones,

I knew about the tow weights and TBD but am interested to understand more about the leaf springs versus the coil springs. Which is better for towing a van and why?

travelyounger · Guru

Hi my old tug was a stock 120 prado tow ball 240 kg towing 2.5 tonne . With coil springs.Airbags were needed to level out the van the ride was a bit bouncy I was using wdh which did help now have a Dmax with Lovells suspension which can handle much more weight and a much better ride when towing but a bit bouncy when unloaded.Leaf Springs would definatly be better for carrying heavier loads and larger tow ball weights and most of the new utes will have to have some extra leaf springs or better shocks to carry this extra weight cheers

dabbler · Guru

Of course I read the OP's comments on vehicles Yobarr. The tables presented all use a derived value which is meaningless in real life. The two vehicles under consideration have different towing capacity and tow ball max. A more meaningful piece of information would be what the caravan manufacturer suggests. Those of us who have investigated this before, know that the percentage used varies from van to van, country to country and yet the only thing that matters is the max legal TBM. My statement still stands.

yobarr · Guru

dabbler wrote:
Of course I read the OP's comments on vehicles Yobarr. The tables presented all use a derived value which is meaningless in real life. The two vehicles under consideration have different towing capacity and tow ball max. A more meaningful piece of information would be what the caravan manufacturer suggests. Those of us who have investigated this before, know that the percentage used varies from van to van, country to country and yet the only thing that matters is the max legal TBM. My statement still stands.

All very good,but there is no way you can safely use a DMax to tow a 3500kg van,with the generally accepted 10% towball weight.It seems that the OP was discussing a DMax,and was merely trying to determine whether towball weight is generally accepted as 10% of GTM,or 10% of ATM.He no doubt now understands that it is 10% of ATM.Cheers. .

Baz421 · Guru

montie wrote:
KevinJ wrote:
Now that I don't trust websites for GTMs, ATMs etc, can I get confirmed that GCM = GVM + GTM and not GCM = GVM + ATM

GCM=GVM+GTM Not correct Montie sounds like you are referring to ACTUAL VEHICLE COMBINATION MASS. GCM is a figure provided by manufacturer,,,, don't muddy the water. Your actual vehicle mass and van actual mass is not to exceed the GCM.

GTM = ATM - Ball Weight.

montie · Guru

Baz421 wrote:
montie wrote:
KevinJ wrote:
Now that I don't trust websites for GTMs, ATMs etc, can I get confirmed that GCM = GVM + GTM and not GCM = GVM + ATM

GCM=GVM+GTM Not correct Montie sounds like you are referring to ACTUAL VEHICLE COMBINATION MASS. GCM is a figure provided by manufacturer,,,, don't muddy the water. Your actual vehicle mass and van actual mass is not to exceed the GCM.

GTM = ATM - Ball Weight.

OK, I'll simplify it...

The measured weight of your tug/van combination cannot legally exceed the lesser of the following:

1) The tug manufacturer's rating if there is one

2) GVM + GTM or GVM + (ATM - Ball Weight).

GCM, GVM and Ball ratings are set by the tug manufacturer. ATM is set by the van manufacturer.

Tones · Veteran Member

Hi Kevin,

I personally prefer leaf springs for towing but having said that, there are many who would disagree and would prefer coils. I own a Dmax and (like many other owners) have written to Isuzu Australia and asked them about whether or not the use of WDH bars will affect Warranty. They (like most of the other manufacturers) respond that they neither "endorse or recommend" the use of such aftermarket devices because they have not been tested with their vehicle designs etc. To be fair, they also acknowledge that some owners may prefer to use such devices and that such use will not necessarily void warranty unless they cause actual damage.

Personally, I would not leave the driveway without bars fitted because of the weight on the ball. Our vehicle is fitted with a genuine towbar that has a certification for a maximum weight of 350Kg. on the ball. Our ball weight averages about 265Kg and there is no way I would even consider towing our van down the highway without bars on. For a start, you would be flat out seeing over the dash. Without bars on our combination, it does not take much giddyup in the road surface to cause concern and lack of stability, not to mention sea sickness. I would not even consider a tow ball weight of anywhere near 350Kg. on our vehicle!!!!!!!!

Some people would argue that coil springs allow the fitment of air bags to beef up the rear end when weight is applied to the tow ball. Whilst this is true, it does nothing to address the issue of redistributing weight back to the steer wheels and the van wheels. Others prefer to stay with leaf springs and beef up that suspension with aftermarket mods.

Perhaps this thread should be about the advertising by manufacturers and the claims by them of what the vehicle is capable of towing. For example (and to prove a point), show me a dual cab of any brand that is rated to tow 3500Kg and let me know how much payload can be put in the tow vehicle when something weighing 3500Kg is dropped onto the tow ball. Of course, that is assuming that there is 350Kg on the ball at the same time. The whole point is........ the GCM rating of the tow vehicle is of CRITICAL importance and determines ultimate limits of actual load in the tow vehicle and this is where the public gets confused!

Tones

KevinJ · Senior Member

Wow, this is all great info for me and stuff I did not know.

I am a software developer as you may start to see as I recently posted a spreadsheet on axle weights; something I had no idea on its significance till I saw the posts.

As part of my research on understanding which tug and caravan suits my wife & I to buy, and also remains legal on weights, I am creating a spreadsheet on the subject.

This is still under development though you will see in the image below, there is a section for what the manufacturers say are their maximums. Then there are three sections for the owner of the vehicle and caravan to put in the actuals (Yellow cells). You will be able to either 1) load the tug to the max and see what is left for the van, 2) load the van to the max and see what is left for the tug, or 3) balance the load between tug and van.

Any red cells will highlight where you are overloaded. The answers will help in my purchase decision and may help with those who already own their tug and van.

In order to test the spreadsheet, I would welcome any tug and/or van owner to send me the following info (Manufacturers settings):

TUG DETAILS
Make and model
Tare
Kerb Weight
Max Payload including TBD
Max GVM
Max Fuel - litres
Max Tow Bar Download (TBD)
Max tow mass (Braked trailer)
Max GCM

VAN DETAILS
Make and model
Tare
Max Payload
Max Gross Trailer Mass (GTM)
Max Tow Bar Download (TBD)
Max Aggregate Trailer Mass (ATM)
Water weight when full
Gas weight when full

I would like to acknowledge the work Amigo1 has done on his spreadsheet. This one is not a replacement, but one that looks at different aspects of this very topical issue.

Once I test the spreadsheet as best as I can, I will post it on the forum for all to use and critique. As always, I will welcome feedback from those more experienced than me on towing.

Just one more thing, I will only be on the forum for one more week till I get back from leave in early October.

-- Edited by KevinJ on Sunday 15th of September 2019 08:46:47 AM

-- Edited by KevinJ on Sunday 15th of September 2019 08:47:15 AM

KevinJ · Senior Member

Unfortunately, due to work commitments, completion of this spreadsheet has to be put on hold. I will complete it as soon as things ease up a bit. I'll be glad to not have work commitments next year sometime.