The Towing question no-one wants to answer

I recently had one of our customers reach out with some questions on towing, which no-one would give them an answer on.  I’ve made a few phone calls and I’m going to try to answer them.

Glossary

This is technical article, so please see a list of explanations of key terms below for reference. Note that these are my interpretations.

GVM – Gross Vehicle Mass – the maximum amount of weight the vehicle can apply down to the ground through the tyres.  It includes all cargo, the weight of passengers, fuels and oils, tyres and wheels and all components on the vehicle.  When towing, the tow ball down weight is also counted as part of the GVM. No matter what, the vehicle must always weigh less than or equal to the GVM.

GCM – Gross Combined Mass – this is the total combined weight of the vehicle and everything being towed, including all cargo, and people.  This is set by the manufacturer of the tow vehicle, and can’t be altered or increased.  In modern vehicle, the GCM is generally less than the sum of the GVM and towing capacity, which means you can’t tow the maximum specified towing weight while the vehicle is loaded to GVM.

Tow ball down weight – this is the weight applied down onto the tow bar (and vehicle) by the trailer. 

Towing Capacity – this is the maximum amount that the vehicle can tow, and is specified by the manufacturer.  It factors the total weight being applied through the tow ball and tow hitch, and includes the tow ball down weight.

GTM – Gross Trailer Mass – this is the Maximum weight applied by the wheels of the trailer onto the ground.  It is the maximum weight that can sit on the wheels of the trailer, and doesn’t include the weight applied down through the towball.

ATM – Aggregate Trailer Mass – this is the combined maximum total weight of the trailer, including tow ball down weight.

Individual axle loads – these are set by the manufacturer of both the vehicle and trailer, and can’t be exceeded, which means that weight distribution is very important.

Situation

John* (not his real name), owns a slightly older 4WD with a 2500kg towing capacity.  He is interested in purchasing a new caravan, but it has an ATM of 3000KG.  In reality, he doesn’t carry that much stuff, so loaded as he intends to use it, the actual ATM it comes in at is 2700KG, with 250KG of that on the towball.

Summary below:

Tow Vehicle:

GVM: 2800KG

Max Tow weight: 2500KG

Max allowed towball downweight: 250KG

GCM: 5300KG

Caravan

ATM: 3000KG                                            ATM as loaded: 2700KG

GTM: 2700KG                                            GTM as loaded: 2450 KG

Tow Ball Down Weight as loaded: 250KG

John’s questions:

  1. If I’m towing a Caravan with a stamped GTM and ATM that exceeds my vehicle’s capacity, but the actual GTM and ATM as I’ve loaded it are lower and stay within the vehicle’s towing capacity, within my GVM and within my GCM, can I tow that van legally?
  2. Given the tow ball down weight is counted as part of the GVM on the vehicle, does this mean that I’m only really towing the GTM, and therefore I can I tow the van legally because if I count the tow ball down weight in what I tow as well, I’m counting it twice?

The Answers

Before I go into this, I want to make it clear that I’m not an Engineer, so while I’ll go into detail in my answers based on plenty of reading, the truth is that there is no clear answer provided by any authority on this matter.  I’ll do my best to identify the challenges and issues, and allow you to interpret that.  Please know that I did make several phone calls to industry experts for their opinion on this…

1. Legally towing a trailer that has a GTM and ATM much greater than your vehicle can tow

The reality is that the GTM and ATM figures stamped onto your van or trailer are a measure of the maximum that a trailer can weigh, but whether what you tow is legal depends on the actual loads, not the theoretical maximum.  So long as the following conditions are met, you can legally tow a van or trailer with a GTM or ATM that exceeds your vehicle’s own towing capacity:

  • Total trailer weight, including tow ball down weight, doesn’t exceed the towing capacity of the vehicle, as specified by the manufacturer.
  • The actual ATM and GTM of the trailer are under the maximum amounts the trailer is allowed (a given in this case, but still important)
  • The individual axle loads on trailer and vehicle are not exceeded
  • The GVM of the vehicle (inclusive the tow ball down weight) doesn’t exceed the amount stamped on the compliance or mod plate.
  • GCM doesn’t exceed the manufacturer set amount.
  • Towball mass doesn’t exceed the maximum amount set by the tow vehicle manufacturer (usually 10% of the max towing capacity, but listed on the tow bar of most vehicles)

Example of how the above might work: If you were towing a car trailer that had an ATM of 4495KG, but a tare (empty) weight of 800KG, and it was towing a 1500kg vehicle, with a 250KG tow ball down weight, and your vehicle had a 2500KG towing capacity with 250KG max towball download, you are OK because the total weight being towed is 2300KG (under the 2500KG limit) and the tow ball down weight is within limits, as long as the 250KG tow ball down weight added to the vehicle keeps it under GVM,  and you don’t exceed individual max axle loads.  GCM is not an issue because you would be under that too in this case.  The key here is keeping under all of the maximum limits allowed on both the vehicle and trailer at all times…

2. Given the tow ball down weight is counted as part of the GVM on the vehicle, does this mean that I’m only really towing the GTM, and therefore can I tow the van legally because if I count the towball downweight in what I tow, I’m counting it twice?

This is the hard question, and one no-one really wants to answer.  The logic here makes sense – surely you don’t count the towball down weight twice?

Unfortunately, the towball downweight does need to factor into both weights because the vehicle wears the down weight by virtue of it ‘sitting’ on the vehicle, but the towbar and tow hitch also has this weight applied to it, in addition to the GTM.

To summarise, to legally tow, you must remain in compliance with all of the following:

Towing capacity – In this case the vehicle is over, because 2700KG of weight is being applied through the tow hitch where the capacity is listed as 2500KG.

GVM – In this case, he is under GVM

Gross Trailer Mass –In this case he is well under the 2700KG GTM – it is at 2450KG

Aggregate Trailer Mass – This is listed at 3000KG, and he is at 2700KG, so well under.

Axle loads – We’ll assume that the loads are OK – the Caravan max axle load would be higher than the maximum GTM which the Caravan is under, and we’ll assume he’s packed the vehicle to work within these limits given he is under GVM for the vehicel by 100KG in this case.

Gross Combined Mass – In this case, the vehicle weighs 2700KG, plus 2450KG for the GTM when attached, so the total is 5150, when the allowed GCM is 5300KG. He’s clear here.

In the above case, the vehicle combination is actually illegal and overweight.  Not because of GVM, GCM, ATM, or GTM, but because the towing capacity has been exceeded.  That is, that the total weight being put onto the towbar and hitch exceeds the manufacturer specifications.  Remember, the towing capacity is 2500KG, although in reality 2700KG of weight is being applied through the towbar.

Now, there is nowhere that provides absolute clarity on this situation, but the failure point here is that the towbar has 2700KG applied to it, even though the down weight is calculated as sitting on the vehicle. If the vehicle had a towin capacity of 2700KG, then you’d be legal even with the 3000KG Caravan, as long as you kept the weight to that level.

Summary

If you are questioning whether your vehicle is legal from a weight point of view, you need to be on or under all of the following limits – remember – being over in one area will mean that technically you are not legal:

  • GVM
  • GCM
  • Tow ball Down weight (max as specified by manufacturer of vehicle)
  • Towing Capacity as stated by the manufacturer (and remember that most modern vehicles can’t be at GVM and tow at the full listed capacity)
  • GTM
  • ATM
  • Individual axle loads

Hope you find this useful! If you are an expert in this area, or have a different point of view, please comment below – it isn’t an easy thing to understand!

Aiden

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Comments 77

  1. I am a little confused here, below is from the article:
    So, if you were towing a car trailer that had an ATM of 4495KG, but a tare (empty) weight of 800KG, and it was towing a 1500kg vehicle, with a 250KG tow ball down weight, and your vehicle had a 2500KG towing capacity with 250KG max towball download, you are OK because the total weight being towed is 2300KG (under the 2500KG limit) and the tow ball down weight is within limits, as long as the 250KG tow ball down weight added to the vehicle keeps it under GVM.

    Later in the article:
    Towing capacity – In this case the vehicle is over, because 2700KG of weight is being applied through the tow hitch where the capacity is listed as 2500KG.

    So where suddenly did the 2700 kg from the trailer come from.

    1. Post
      Author

      Hi Norman, thanks for reading. I am referring to 2 different scenarios here. The 2700kg one is the original scenario where the guy is trying to tow a 2700kg trailer with a vehicle that has a 2500kg tow capacity. The other scenario is the car trailer one. Different – sorry if it was confusing!

      1. Hello Aiden, in the introduction to the article you explained the various terms. Unfortunately you made an error in your description of Gross Combined Mass (GCM). You stated that it cannot be changed. That is incorrect. My Toyota 200 series Landcruiser has had a Gross Vehicle Mass upgrade to 5800 kg and a GCM upgrade to 7300 kg. I have the Engineering certificate and the compliance plate is attached to the vehicle. The suspension company, Lovells, supplied the components and my local suspension expert installed them.

        Kind regards,
        Anton.

        1. Post
          Author
          1. Where I work we do the upgrade as well. Not all vehicles can have it done but there are a lot that can upgrade

    2. My question is in regards to the electric braking capacity of a trailer. Lets say a trailer has a GTM of 1600kg and has 150kg on the ball, giving ATM 1750kg.
      Do the trailer brakes need to be rated at 1600kg or 1750kg. In other words does the brake capacity of the trailer need to meet the GTM or ATM?

      1. Post
        Author

        Hi Ian, good question! I’ll have to find out, but I think it would have to be ATM because the brakes need to be able to hold the trailer when uncoupled from the vehicle…

      1. Post
        Author

        Hi Joseph, thanks for the comment. It actually is correct – I set that up to demonstrate that you can actually tow a trailer with an ATM much higher than the vehicle, as long as it is only loaded to a level that is within the vehicle towing limits.

    1. Post
      Author
  2. Very helpfull article.

    I have the some delema in finding out if I am legal towing my fifth wheeler. Even the technical dept of the RMS keep referring me to caravan formulas which is not correct as with fifth wheelers the tow ball weight is over the rear axle.

    If you like my specific information. I would be more than happy to provide it

    Regards
    Peter Pile
    0452268223

    1. 5th wheelers are a lot easier, the weight you place on the table of your vehicle is counted towards GVM . Towball load is not a factor. You need to weigh your van and make sure that when it is all connected up it doesnt exceed the GCM of your particular vehicle, and when loaded it doesnt exceed your vehicles payload or GVM. You may find the weight your van puts on the table of your vehicle could be 400kgs or so. Hope that helps. Not an expert just know someone who owns one and he explained it to me only a couple of weeks ago.

  3. Force is a vector – direction and magnitude. If have 2450 towards the van and 250 down the resultant vector force is in fact 2463 kg. Square root of 2450 squared + 250 squared.

    So if you do add the forces then this is what you end up with however it does not make sense as two bars are rated at a down force AND a growing force.

    1. Post
      Author

      Hi Peter, thanks for the comment. Maybe Force was the wrong word? What I was trying to say was that the towbar wears the weight of the trailer and the towball downforce, and therefore it needs to be included in the towing capacity, not just the GTM.

      1. I did a lot of research into this when i had a ute towing my van and found no ute could carry or tow in combination what is specified so went to a VW Touareg V6 which allows the GVM and the ATM to be within the SPECIFIED GCM

    2. The 2450 is the downward weight on the axles. 2700 total trailer weight minus the weight taken by the tow ball. both are vertical “forces”. The equation you use above only applies if the 2450 is horizontal and the 250 vertical. If this is the case then you use Pythagorus to get the combined force with a direction between the two. But this is not relevant here unless in a crash/under acceleration/under braking when a forward force on the tow ball would exist due to the weight of the trailer, but not the full 2450. However that is still not relevant to the legality issue at hand only to the forces being exerted on the tow ball in a given situation. To calculate these, you would need the height of the towball, all the dimensions of the ball to account for bending moments, vertical centre of the trailer load relative to the ball, acceleration (+ve or -ve), incline of the road. As a quick response I think that is all you would need to calculate the forces on the various parts of the tow ball.

  4. The whole article is confusing, but that’s no fault of the author. Rather the complex nature of vehicle and tow weights.

    I’d be interested to see if there is any case law in either civil or criminal jurisdictions on this. Ultimately it’s the courts that will decide.

    Surely some where around the country at some point a collision involving overloaded vehicles and/or trailers has been before a court.

  5. It is straight forward. Even if he wanted to tow a van of 3000kg and a tow ball down weight of 500 kg. It’s still towing 3000 kg not 2500 kg that his car would allow

    1. Post
      Author

      Yep – if he could get the trailer to weigh 2500kg, no worries. The confusion in this case comes from the tow ball down weight and whether it counts towards the towing weight given it is sitting on the vehicle… unfortunately the tow limit includes the tow ball down weight

      1. You are correct on all points Aiden.
        To make it simple, view the towing weights as two dimensional, ie two separate numbers. The vertical weights and the horizontal weights . They are forces acting in different directions! Your vehicle will have its stated capacity for both.
        It’s sooooooo important to get your numbers correct in all areas. Think of your BW,ATM, GTM, GCM, your axle weights for both trailer and tug and even your tyre loadings on both as a Venn diagram where you can only operate within the intersection of the circle parameters.

  6. Hi Aiden
    Hi Aiden
    Greg Merrick here, that had this initial lengthy phone discussion with you last week.
    Its a very difficult scenario to explain to others (I think you have done very well with your article)
    After our discussion my wife and I decided to no longer tow with our Prado. So we went out and bought
    a new Bi-Turbo Ranger that ‘ticks all the boxes’ towing wise.
    Thank you for your time and input (you are the only Consultant that has understood my question, and has given me a sensible in-depth answer.
    Regards Greg Merrick 0402 434 052

    1. Post
      Author
  7. Hi Aiden

    I think if you read your article carefully you have nailed it.

    I had my 2016 Ranger XLT and Jayco OB 19 foot caravan weighed by a mobile caravan weighing company service here in WA, just before setting off on my last trip. Their calculation for GCM is GTM + GVM, where the Tow Ball Mass is included in the GVM. The whole setup only weighed the above. Therefore the TBM was only counted once for the total weight on the ground. As stated all things relating to the ATM are acting on the tow ball. Therefore surely the GCM should be the GVM + the ATM which means the tow ball mass is taken into account twice.

    As an aside the weighing company said that I was one of only 45% of caravans they had weighed that was legal to be on the road. I wonder how much that percentage would drop if they used the the ATM instead of the GTM for their GCM calculations. (Just in case anyone asks was I still legal, as I add the ATM to the GVM for my own calculations and was still under the legal side of things by 300kg)

    Regards

    Mike

  8. Hi Aiden

    A great article and there is so much to take into consideration, no wonder so many people get it wrong, your explanation is very good and reasonably clear considering, the complexity of the subject. The number of people I see that buy a van thats right up to the tow capacity mentioned by manufacturers is amazing. The manufacturers need to take responsibility here and actually put realistic numbers within there manuals, I dont know any vehicle that can realistically tow to its mentioned capacity.

    thanks

    Chris

  9. Aiden, do you know if the GVM is the actual weight of the car or do the police assume weights for the number people the vehicle can hold? I read somewhere that a person was booked for being over under those conditions, even though he was the only one in the car. Good article on a very complex issue.

    1. Post
      Author

      Hi Shane, GVM needs to include people as they are part of the payload. Not sure if Police would guess passenger weights, but you need to factor them in technically…

  10. Sounds like to me the laws are so complicated, that they are all for interpretation to what the police or Motor vehicle registry (or whatever you state calls it) and you interpret it as. The laws in Australia is so messed up it is not funny. Cleary written by lawyer academics to make it virtually impossible for the average person to understand.

    I am going through this stage now with the new laws in the NCOP regarding suspension lifts and ESC vehicles. Especially with the territories interpretation and what they want to do. All I can say is thank god I live in a state where we have common sense and the rules are slightly lapsed to apply this. I must say the MVR here are being extremely helpful in this matter, and are willing to get me over the line the easiest way possible for everyone. Lets hope that’s how it pans out when I am back in town to sort it out.

  11. The towball down force stands on its own. The vehicle designer calculates the strength of the tow bar based on the maximum down force and the expected forces from accelerating the maximum towed weight. So each weight stands on its own e.g.. If your van weights 3500 kg with 350 kg down force and your vehicle can tow 3500 kg and have a towball load of 350 kg then you are ok for these two tests. You do not add towball weight weight to towed weight as this makes no technical sense.
    If you pass these tests then you need to check off all the others e.g.. axle loadings, GVM, ATM, ………

    1. Post
      Author

      Thanks for the info here. However, when you are talking weight, the question is does your weight of the van include the tow ball down weight? We have to assume yes, because the tow bar is still subject to that weight…

  12. I found this interesting article about “EVERYTHING YOU NEED TO KNOW ABOUT TOWING HEAVY TRAILERS” see link below. It also explains how towball down load effects vehicle axle load and gives the following example

    Rear axle load as a result of TBM = (Overhang / Wheelbase) * TBM

    For example, 1200mm overhang, 130kg TBM, 2750mm wheelbase = 57kg reduction in weight on the front axle. Add that to the TBM of 130kg and we have 187kg on the rear axle.

    https://practicalmotoring.com.au/car-advice/everything-you-need-to-know-about-towing-heavy-trailers/

  13. I think you’ll have difficulties demonstrating all the science to an insurance company assessor in the case of an accident, especially if the van has been significantly damaged. I saw a caravan that had flipped at speed once, and I reckon you’d be hard pressed to find the compliance plate amongst the carnage let alone show you’d loaded under the ATM. There’s street legal, and then there’s insurance legal!

  14. The problem with this scenario is that you haven’t taken into consideration any payload in the vehicle. This quickly adds up once you add passengers, bull bars, tow bars, dual battery systems and the like. Not to mention luggage , groceries and that hefty two slabs of beer!

    1. Post
      Author

      Hi Jason,

      Totally agree, but this article was about the trailer/van. Payload is definitely an issue, and one that quickly ads up. We’ll have an article on managing it in the real world soon…

  15. It seems that each different limit is to avoid overloading a different component of the vehicle. If any individual component fails it could end very badly, this is why you need to keep them all under.

    GVM – towing vehicles suspension
    GCM – drive train/brakes/road or bridge limits
    Tow ball down weight – vertical forces on tow bar
    Towing Capacity (max ATM) – horizontal forces on tow bar especially in collision
    GTM – trailer suspension
    ATM – horizontal forces on tow bar especially in collision
    Axle loads – suspension/axle capacity/road pressure

    1. I think the biggest confusion comes from the understanding of trailer mass. If you sat your unhitched, loaded trailer on a set of scales, the number indicated would be its gross trailer mass. That mass would be the sum of the down force of the points of contact with the ground (or scales). There would be the weight recorded at the wheels, and also the weight recorded at the jockey wheel (or drawbar if it was resting on the ground). The weight at the drawbar can be changed just in the way it is loaded, especially with single axle trailers. So a trailer with a total loaded weight of 2700kg might have 2500kg on the axles and 200 kg on the drawbar.
      Your car will still have to pull that 2700kg, but it must also be able to have that 200 kg ball weight as part of its own payload (gross vehicle mass minus its tare weight). If the rated payload is 900kg, and you’ve stuck 200kg of towball downweight on it, you now only have 700kg to play with, which includes all your fuel, accessories, you, the missus and the kids.

  16. Thanks for the article. I haven’t read all of the questions and answers above but one critical question for me is what are the consequences of not being legal? In particular, would the car and van/trailer be covered by insurance or would the policies be void? Any other consequences? Fines? Cheers

    1. Post
      Author

      Hi Lisa,
      All insurance policies are likely to have a clause that talks to being overloaded. Basically, if you have an accident and it is determined that the vehicle or trailer you were towing was overloaded, then you’d likely have to prove that it didn’t have anything to do with the accident, or you could have a claim reduced or refused.

  17. Stability!
    The mass of the 2700 kg van is swinging off the back the car. The weight the axles carry is only part of the stability equation. When/ if the van starts to sway, 2700 kg will be trying to pull the 2700 kg of the car from side to side. The car’s mass is not more than the caravan so it will struggle to win in a push-pull/left-right fight with the van which is probably longer than the car.(bigger leaver)
    Stability is the key here not just weight.
    A fifth wheeler can be more stable because the swinging mass of the van is not pulling from a point behind the rear axle, but is working on a point between the car’s front and rear.

    1. Hi Mick,
      That’s why it is important to have a tow vehicle heavier than the van/trailer it is towing. How some of the smaller/lighter tow vehicles gain high towing capacities is alarming.

  18. Aiden just to complicate it further with a Patrol (Y61) if you have a towball download of 250kgs you reduce your vehicle GVM by 100kgs not 250kgs There is a scale printed on your inside rear door and manuals so to say your GVM is reduced by your ballweight is not quite true in all cases

    1. Post
      Author

      Yes Elaine – I’m aware of that. Nissan is the only brand I know where they reduce the GVM you can have based on towball downweight. I didn’t mention that here because it is the only make I’m aware of that does this, and I didn’t want to complicate things further, but you are 100% correct!

  19. Hi Aiden.
    Thank you for a well written article. I will be sharing it often.
    I worked at a business that had 7 very different trailers that contractors would tow.
    It is the businesses responsibility to not allow the contractor to overload.
    With the varied vehicles, loads they carried, plus the trailer weight, and the contractors “Belief” about towing. This was a challenge at first.
    A set of scales were bought so any time a vehicles weight was a question it would be weighed, the trailer weights were known, and we used the same above formula (simplified) as the rule.
    GVM + GTM Must be less than GCVM less 200kg for safety.
    Over time there were accidents and some vehicles and trailers weighed by the authorities.
    They alway were within load capacities.

  20. A little out of left field, is there a minimum towball downforce requirement? Going negative is not acceptable but a light weight can improve the ride!

    1. There is no legal minimum but a very light ball load can mean a very unstable trailer as the loaded mass is in a rearward condition.
      It is generally accepted and some car manufacturers have it in their handbooks, that a ball weight of around 10% of the trailer ATM will create a stable towing platform

    2. I have two concerns
      – Do our different states and territories have diiferent ways of interpreting and enforcing these rules
      -Do the different insurance companies access claims differently.
      Perhaps ring your insurer and get a written response.
      I have a Jeep GC petrol with a towing capacity of 2812kg and a Bailey slideout ATM 2800kg. Also I have a weighing device that I use to weigh all car and caravan wheels and tow ball weight when loaded just to make sure all the parameters are under what is required. I have these weight recorded in case I am queried.
      I think towing a van with a rated ATM above the car’s towing capacity would be very risky and expensive in some states and if you have an accident.
      My feelings are that it is not worth the risk even if you pack light.

  21. I don’t find the math that confusing. The tow ball weight must be considered in 2 seperate formulas but its not counted twice as such. If your vehicle has a 3000kg tow capacity, then that obviously includes ball weight of said trailer/caravan. Axles + Ball weight. That is your ATM.
    If your vehicle has a GVM of 3000kg, then the Tow Ball Weight has to be included in that formula as well. It’s part of the actual load ON your vehicle. However, the GCM, Gross Combination Mass, does not include the Tow Ball Weight x 2.
    A public weighbridge will weigh all combinations for you to establish if your weight distribution/loading is legal, but YOU need to know those maximum manufacturers weights.

  22. Jayco would not sell me a caravan which had an ATM which only slightly exceeded my vehicles towing capacity. Even if I ensured that the towing capacity would not be exceeded they advised that in the case of an accident an insurance company would assume that you were at lest loaded to the ATM and if this exceed your vehicle’s towing capacity they would deny insurance cover. How many people load up to their maximum ATM with empty water tanks and think they are OK. I have been advised that insurance has also been declined as they assume the tanks would have been full.

  23. I have been going over the article and comments on towing weights. Nowhere is it mentioned that any passengers that are going to be travelling in the vehicle MUST also be included in the weighing stats.
    Without taking this into consideration could mean a hefty fine and some passengers starting a long walk.
    HINT!!!
    A little bit of info that could come in handy to those part time vaners. If you adjust your van brakes so that they come on just before your towing vehicle brakes it will always keep both vehicles in a straight line. If your caravan starts to sway just a touch on your brakes, so the trailer brakes come on only, will bring your caravan back inline. Do not accelerate thinking this will brink the trailer into line. gently gently on the brake

    1. The driver and passengers are always included in the payload of your vehicle. So four adult males in the vehicle averaging 90kg each is 360kg off your payload capacity.
      The article didn’t touch on that since it was about the towing legalities of the vehicle and overall weights.
      Dependant on what state or territory you are in. The number of empty seatbelts can be used by a police officer or a heavies inspector to determine you are overweight. This is because most states have a minimum weights schedule for occupants.
      You may 100kg under the allowed gvm/gcm scenario with just you and the missus. But have three spare seatbelts. If you picked up 2 people who were broken down you are now overweight. This why some people have been fined for being overweight. Though most heavies I talk to. Will give a warning saying your not allowed to take any passengers. Usually in writing.

    2. I believe this assumption in relation to the Patrol to be incorrect. In this case the GVM has been downgraded by 100kg and you still have a 250kg load added to the actual VM. You are 100 worse off not 150 better off.

      Aiden in your case where you say the vehicle is illegal and overweight I would suggest the latter be deleted. People need to read the definition of ATM and all thoughts of design forces, vectors etc can be forgotten. The tow bar capacity relates to both what it can support vertically (max ball weight) and what can swing off it in any direction i.e. the ATM.

    3. Rod you have missed the crucial point. The capacities quoted by manufactures are maximums. Therefore you have to add the actual payload to the tare weight in each case to see if you are compliant.

  24. I have been a caravan and trailer dealer for 40 years. I am pleased you have broached the issue of towball download in calculations. My understanding is you are counting it twice as GCM is weighing the combined unit in one motion. Tow at makers provide the two weights download and tow load as separate items. I think the Nissan 100 kgs would make a logical allowance.
    Some European caravans have overide brakes approved to 2000 kgs Gtm yet are registered with ATMs of 2120 kg , so the ball weight is not included. I still get confused by RMS interpretations.

  25. Sadly guys like John are few and far between. in my travels I often use towing weights as a conversation starter, It seems that 70% of people towing have no idea what their van weighs or what their vehicle can legally tow.

    Hopefully articles like this encourage them to to get the weights right. but just because the max have not been exceeded doesn’t mean it’s a good idea, the max limit may be ok for a short trip but not when your towing for the big lap.

    IMO towing the max weight is like hey the red line on the tach is 5000rpm so I can sit on 5000rpm all day, not good.

  26. Great article which highlights the complexity of towing caravans and the issues that have to be addressed in buying a tow vehicle. Keep in mind that a dealer cannot sell you a caravan if your tow vehicle cannot legally tow the ATM, with the tow ball mass also within the manufacturer of the tow vehicle limits and also the GCM within the manufacturer limits. Consumer agencies are making dealers responsible in most states and there are increasing calls for this across the country. Even if a purchaser believes he will never load the van to the ATM the dealer will not be able to sell the van to him or her. Then of course we need to consider the huge number of vans that have a discrepancy between the nominated weights from the manufacturer and the actual weight of the van. All consumers should load their van and car up to go away and then go to a weighbridge and check the GCM, GVM and GTM are within the legal limits.

  27. I may be going off on a completely different tangent hear but, I personally always believed that a tow capacity of the vehicle not only included the ability of suspension (and tyres) to carry the weight as mentioned above. But, also the tow vehicle’s ability’s to safely pull and slow the combined mass.
    Based on my belief the original question is a given “No” it is not a legal combination. The idea might seem simple given all the explanation over ball weight AGM, GVM, GCM. But sometimes simplicity errs, on the side of caution.
    I do understand that modern tow vehicles and vans use electric brakes that by design should combine to ensure safe ‘over’ braking capacity, but braking ability is still a consideration in the event of a traffic crash involving an articulated vehicle. And importantly any consideration may be used for a legal interpretation.

  28. This is a great discussion, one that needs to be had. However, there is an elephant in the room, the falsification of VIN plates weights by manufacturers & dealers alike. Trust me, I worked in the RV industry for nearly a decade & it is more common than you think.
    I feel sorry for the poor buyer as they think every weight criteria they meet according to their VIN plate is legal when in fact it isn’t.

  29. Great article.
    It’s funny is it not that the tow ball weight is one of the most misunderstood things and probable the hardest to get an accurate measurement of. I have a set of tow ball weight scales, so I always measure it before leaving on a trip. I make sure that when I take the measurement that the drawbar hight is close to the same as when it’s sitting on the tow ball. I have now found that in fact because I use weight distribution this figure is in correct or at least erroneous, the weight distribution shifts weight from the tow bar to both the front wheels of the tow vehicle and the main wheels of the caravan. You can only find out this effect by traveling to a weight bridge and weighting the combination of van and vehicle and then disconnecting, weighting it all again. We end up with a shift of around 33% to front axle tow vehicle 23% to caravan wheel set when the weight distribution is applied. Hope this helps someone as it can make a difference if you are getting close to your caravan or vehicle weight limits. Also you can have the GCM of some vehicles upgraded as the mining companies need this with some of their vehicles on mine sites, I no the Ford Ranger is one. I understand some state governments where going to ban this but the mining companies had strong objections and to my knowledge the government’s backed down.

  30. Does the same theory apply to tow ball weight? My European car has a 75kg limit on the tow ball. If I tow a caravan that has an 80kg tow ball plate can I balance the van so I actually achieve a 75kg tow ball load and be legal? So is the weight shown on the plate a maximum?

    This would be with a European van that does not use the 10% ball weight theory like Australian vans.

    1. Post
      Author

      HI William, technically yes, you can, but you also need to consider weight distribution – taking weight off the vehicle could affect handling and the ability of the vehicle to tow the van safely. You’d need to consider this in the context of overall weights of the tow vehicle and the towed trailer.

  31. The Towing question no-one wants to answer

    It seems to me that this question will just keep going around & around.
    An insurance loophole.
    As an Insurer you would think you could answer it so people that insure their vehicle & caravan know where they stand.
    The simple fact is that the problem lies with the Caravan Manufacturers.
    They are building caravans that are simple too heavy and exceed the capacity of a regular Four Wheel Drive.
    You might not want to say it, but they are building caravans that are not suitable to be towed by a normal four-wheel drive.
    Hence, if you take note of any caravaning show that is aired today on TV they are being towed by a Dodge Ram Truck or similar not a regular Four Wheel Drive that is because they have the capability to tow a heavier weight.
    This problem only arose when caravan manufacturers started making the interior of your van like your Kitchen at home, looks nice and fancy but boy does it add a lot of weight.
    So the question remains, Am I still legally allowed to tow this Van of mine??
    Simple answer is NO. Not if you want an insurance payout.

  32. Good article Aiden, particularly in that it raises the often misunderstood question of weights when towing. I have had discussions over this definition on numerous occasions. A VASS Engineer who specialises in the caravan industry indicated to me some time ago the following definition. It specifies it is incorrect to count towball mass (TBM) twice.

    “Vehicle Standard (Australian Design Rule – Definitions and Vehicle Categories) 2005 definition of GCM is as follows:

    GROSS COMBINATION MASS – value specified for the vehicle by the ‘Manufacturer’ as being the maximum of the sum of the ‘Gross Vehicle Mass’ of the drawing vehicle plus the sum of the ‘Axle Loads’ of any vehicle capable of being drawn as a trailer.”

    The GVM when drawing a trailer includes the TBM and the trailer axle loads comprise the rest of the weight to determine the GCM. (My comment)

    In the interest of full disclosure I run a mobile weighing service in Melbourne. http://www.weighstation.com.au

  33. I really don’t understand why the definitions are confusing, they are very simple definitions and have written articles on this myself. The biggest problem that arises in the real world is that many van manufacturers do not weigh each van individually and customers are unknowingly dealing with a tare weight which is much higher than plated and little “wriggle room” for loading to GTM and without weighing their loaded rig exceed the legal limits very quickly (plus the fact that the old “standards” of 300kg payload for 1 axle and 400kg for tandem is way too little for today’s full time travelers)

  34. Whew, just read through all this – what a mess this area is.
    However, what struck me early on in the original article, is the
    “but whether what you tow is legal depends on the actual loads, not the theoretical maximum.”

    Where does that fit with the principal of “I know officer, that this light truck has a GVM of 8ton and I don’t have a heavy vehicle endorsement on my license, but it is empty, and only weighs 3600kg, so surely I can drive it on my car license”

    I know there are specific laws to prevent this action, but they are based on the ‘Theoretical maximum GVM’ of the truck and have nothing to do with the actual weight of the truck at the particular time that it is inspected.

    1. Post
      Author

      Hi Michael,

      Interesting point you make, although the reference is in regards to towing vs driving a vehicle bigger than allowed. We’ll seek some clarification here…

      Aiden

  35. Great article
    Good to hear all the different views I still believe to trailer shouldn’t be heavier than the tow vehicle

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