How are towing capacities determined?

Mein · Senior Member

How are towing capacities determined?

Whenarewethere · Guru

Technically... throwing dice in the air or engineering will do 3d simulations of the metal properties of the car.

My car has a maximum tow ball limit of up to 350kg up to 100kph on sealed roads, but the car can only tow 2000kg or 750kg payload on non Gazetted roads.

They are useless numbers as the car only has a payload of 500kg. My car is a small car. A LandCruiser which is a very large car has a payload of I believe 615kg. Which for a very large car is even more useless. Cars with 7 seats loaded with passengers are usually over their payload.

Then there is rear axle load. For it to work with maximum tow ball weight you need to lose weight & move the driver's seat forward & the only thing one can carry in the boot is helium balloons.

Unless one has a PhD & double MA in weights & measures, keep all masses less than 70% of marketing BS & one should hopefully be safe!

Hitting the road · Senior Member

Towing capacities are questionable in many cases imo. No way would I be towing a 3500kg weight behind a dual cab ute that boasts 140kw of power and weighs a tonne less than the load! Classic example of the tail wagging the dog.

The towing capacity is directly linked to the Gross Vehicle Mass of the vehicle along with the manufacturers Gross Combination Mass figures.
As the tow vehicle itself is loaded toward the manufacturer's vehicle GVM, the GCM is directly affected.

As far as how manufacturers determine towing capacity I doubt very much there is any formula as such. I'd reckon it would be totally dependent on the calculated strength of the chassis or unibody construction and the materials used, alongside the manufacturers intended use of the vehicle, and i would hope the vehicle's actual physical weight.

deverall11 · Guru

Can someone confirm if it is a legal requirement to have a vehicle with a towing capacity of 3.5t
to tow a 3.5t rated van even though it will never get to that weight.
In other words can you use a vehicle rated at 2800kg to tow said van as long as
the van does not go above that weight.
I have heard many instances where an unsuspecting buyer bought a 3t van, turned up
with a vehicle similar to a Ford Falcon and was given the green light by the sales person.

watsea · Guru

I do not know how the manufacturer determines the towing capacity but even with the ones listed in the first post, those vehicles with front wheel drive only, tend to have a less tow capacity than a comparable weight, power/Torque capacity rear wheel drive vehicle. That's easy to understand why.

This probably applies that AWD vehicles have a higher capacity than rear wheel drive only. I think that applies to Ford Territories??
How does that apply to some of the ute variants say, Dmax or Ranger, 2wheel drive vs 4wheel drive? What happens if the driver does not engage the front hubs if that option applies?

Rob Driver · Guru

If it was written law to have a set maximum ratio of weight between the towing and the towed unit then vehicle manufacturers could not overstate the ability of their vehicle to tow a stated weigh dependant upon HP braking ability and other engineering design.

The manufacturers marketing team currently have a loophole that permits the consumer to believe that his or her vehicle can automatically tow a trailer of a certain weight.

To answer at least part of the question it is the manufacturers engineers that make these claims and they are blindly accepted into our current *towing folk law* and our respective governments.

bratboy · Veteran Member

deverall11 wrote:
Can someone confirm if it is a legal requirement to have a vehicle with a towing capacity of 3.5t
to tow a 3.5t rated van even though it will never get to that weight.
In other words can you use a vehicle rated at 2800kg to tow said van as long as
the van does not go above that weight.
I have heard many instances where an unsuspecting buyer bought a 3t van, turned up
with a vehicle similar to a Ford Falcon and was given the green light by the sales person.

The only legal requirement is that you stay under the rated capacity of your tow vehicle .

so in your example vans atm is 3.5 t ,tow vehicles max towing capacity is 2.8 t as long as the actual weight of the van doesn't go over 2.8 t your fine .

KevinJ · Senior Member

bratboy wrote:
deverall11 wrote:
Can someone confirm if it is a legal requirement to have a vehicle with a towing capacity of 3.5t
to tow a 3.5t rated van even though it will never get to that weight.
In other words can you use a vehicle rated at 2800kg to tow said van as long as
the van does not go above that weight.
I have heard many instances where an unsuspecting buyer bought a 3t van, turned up
with a vehicle similar to a Ford Falcon and was given the green light by the sales person.
The only legal requirement is that you stay under the rated capacity of your tow vehicle .
so in your example vans atm is 3.5 t ,tow vehicles max towing capacity is 2.8 t as long as the actual weight of the van doesn't go over 2.8 t your fine .

That's correct.

bratboy · Veteran Member

KevinJ wrote:
bratboy wrote:
deverall11 wrote:
Can someone confirm if it is a legal requirement to have a vehicle with a towing capacity of 3.5t
to tow a 3.5t rated van even though it will never get to that weight.
In other words can you use a vehicle rated at 2800kg to tow said van as long as
the van does not go above that weight.
I have heard many instances where an unsuspecting buyer bought a 3t van, turned up
with a vehicle similar to a Ford Falcon and was given the green light by the sales person.
The only legal requirement is that you stay under the rated capacity of your tow vehicle .
so in your example vans atm is 3.5 t ,tow vehicles max towing capacity is 2.8 t as long as the actual weight of the van doesn't go over 2.8 t your fine .
That's correct.

I know biggrin

Mein · Senior Member

"The only legal requirement is that you stay under the rated capacity of your tow vehicle ."

In the 60s and 70s, in Victoria, my family had caravans which my father towed with Holden wagons - an EH and a HT.

I can specifically recall one day asking my father what size van our car could tow and he told me that the legal limit was 1.5 times the weight of the towing vehicle.

Of course, I accepted what my father told me without question and, in any event, there was no internet or other easy way for me to check for myself.

Interestingly, you can see above that the Nissan Navara D40's specified towing capacity is 1.5 times it's own weight.

When I started towing caravans in the 90s, an engineer friend told me that the weight of the towed vehicle should never exceed the weight of the towing vehicle.

KevinJ · Senior Member

My apologies if a second opinion was not warranted. I'll keep future ones to myself.

Jaahn · Guru

Here are the regs from the NSW RTA page. https://www.nsw.gov.au/topics/roads-safety-and-rules/vehicle-safety-and-compliance/towing-a-caravan

I believe they were harmonised with most other states some years ago. Jaahn

Towing ratio requirement

The loaded mass of the trailer must not exceed the lesser of:

rated capacity of the towbar and tow coupling
maximum towing capacity of the vehicle
maximum carrying capacity of the trailer
maximum rated carrying capacity of the tyres.

If the vehicle manufacturer has not specied the maximum towing mass, the maximum towing mass is:

one and a half times the unladen mass of the towing vehicle, provided that the trailer is fitted with brakes which are connected and in working order, or
the unladen mass of the towing vehicle if the trailer does not require brakes.

Vehicles with a manufacturers gross combination mass (GCM) more than 4.5 tonne may tow in accordance with the above requirements. The GCM is the gross combination mass of the car and loaded trailer.

-- Edited by Jaahn on Tuesday 22nd of March 2022 04:09:43 PM

oldbloke · Guru

Jaahn wrote:
Here are the regs from the NSW RTA page. https://www.nsw.gov.au/topics/roads-safety-and-rules/vehicle-safety-and-compliance/towing-a-caravan
I believe they were harmonised with most other states some years ago. Jaahn
Towing ratio requirement
The loaded mass of the trailer must not exceed the lesser of:
rated capacity of the towbar and tow coupling
maximum towing capacity of the vehicle
maximum carrying capacity of the trailer
maximum rated carrying capacity of the tyres.
If the vehicle manufacturer has not specied the maximum towing mass, the maximum towing mass is:
one and a half times the unladen mass of the towing vehicle, provided that the trailer is fitted with brakes which are connected and in working order, or
the unladen mass of the towing vehicle if the trailer does not require brakes.
Vehicles with a manufacturers gross combination mass (GCM) more than 4.5 tonne may tow in accordance with the above requirements. The GCM is the gross combination mass of the car and loaded trailer.

-- Edited by Jaahn on Tuesday 22nd of March 2022 04:09:43 PM

So, in some circumstances the Government, and its advisors including engineers think its safe to tow a van/trailer upto 50% heavier than the tug.

I find this most interesting considering all of the "noise" made by some members here that if the tug is not I think, 10% ? heavier than the van it is a death trap.

Mmmm I wonder who is right? I wonder who is full of lets say, "hot air"?

iana · Guru

I think the 3.5t towing capacity comes from vehicle licensing in Europe. Over there once the vehicle exceeds 3.5t, the driver has to go for a different license. So the vehicle are rated to 3.5t to get their sales, over that sales would be limited. Quite happy for others to expand on this.

Radar · Guru

oldbloke wrote:
Jaahn wrote:
Here are the regs from the NSW RTA page. https://www.nsw.gov.au/topics/roads-safety-and-rules/vehicle-safety-and-compliance/towing-a-caravan
I believe they were harmonised with most other states some years ago. Jaahn
Towing ratio requirement
The loaded mass of the trailer must not exceed the lesser of:
rated capacity of the towbar and tow coupling
maximum towing capacity of the vehicleI
maximum carrying capacity of the trailer
maximum rated carrying capacity of the tyres.
If the vehicle manufacturer has not specied the maximum towing mass, the maximum towing mass is:
one and a half times the unladen mass of the towing vehicle, provided that the trailer is fitted with brakes which are connected and in working order, or
the unladen mass of the towing vehicle if the trailer does not require brakes.
Vehicles with a manufacturers gross combination mass (GCM) more than 4.5 tonne may tow in accordance with the above requirements. The GCM is the gross combination mass of the car and loaded trailer.
So, in some circumstances the Government, and its advisors including engineers think its safe to tow a van/trailer upto 50% heavier than the tug.
I find this most interesting considering all of the "noise" made by some members here that if the tug is not I think, 10% ? heavier than the van it is a death trap.
Mmmm I wonder who is right? I wonder who is full of lets say, "hot air"?

Vehicles can operate under license which could throw threr argument out the door,

Ie, you see those trucks towing quad axle dog trailers, rough figures truck 22.5 tonnes, the quad dog 30 tonnes operating on a license, a piecie of paper.

Just thought I would throw that unsafe vehicle in the equation.

Radar · Guru

iana wrote:
I think the 3.5t towing capacity comes from vehicle licensing in Europe. Over there once the vehicle exceeds 3.5t, the driver has to go for a different license. So the vehicle are rated to 3.5t to get their sales, over that sales would be limited. Quite happy for others to expand on this.

Iana.

No, I differ, 3.5 tonne towing come about by the Asian translation of our road rules.

Toyota and Nissan were more on the mark earlier.

Our 2013 Nissan Narava gvm 3020 kgs, gcm 6020 kgs with 3 tonne towing, 300 towball weight.

-- Edited by Radar on Wednesday 23rd of March 2022 07:38:41 AM

Rob Driver · Guru

oldbloke wrote:
Jaahn wrote:
Here are the regs from the NSW RTA page. https://www.nsw.gov.au/topics/roads-safety-and-rules/vehicle-safety-and-compliance/towing-a-caravan
I believe they were harmonised with most other states some years ago. Jaahn
Towing ratio requirement
The loaded mass of the trailer must not exceed the lesser of:
rated capacity of the towbar and tow coupling
maximum towing capacity of the vehicle
maximum carrying capacity of the trailer
maximum rated carrying capacity of the tyres.
If the vehicle manufacturer has not specied the maximum towing mass, the maximum towing mass is:
one and a half times the unladen mass of the towing vehicle, provided that the trailer is fitted with brakes which are connected and in working order, or
the unladen mass of the towing vehicle if the trailer does not require brakes.
Vehicles with a manufacturers gross combination mass (GCM) more than 4.5 tonne may tow in accordance with the above requirements. The GCM is the gross combination mass of the car and loaded trailer.

-- Edited by Jaahn on Tuesday 22nd of March 2022 04:09:43 PM
So, in some circumstances the Government, and its advisors including engineers think its safe to tow a van/trailer upto 50% heavier than the tug.

I find this most interesting considering all of the "noise" made by some members here that if the tug is not I think, 10% ? heavier than the van it is a death trap.

Mmmm I wonder who is right? I wonder who is full of lets say, "hot air"?

Hi oldbloke,

I think the biggest problem we are forced to recognise is that from that burst of *hot air* we are all towing vans weighing 3.5 tonne with a mid size ute and with 350 kg on the tow bar and that is before anyone uses a WDH.

In the real world there are so many towing vans that are a lot lighter in weight than what may be the maximum allowable figure.

iana · Guru

European BE licence:- Without prejudice to the provisions of type-approval rules for the vehicles concerned, a combination of vehicles consisting of a tractor vehicle in category B and any number of trailers or semi-trailer wheres the maximum authorised mass of the trailer(s) or semi-trailer(s) do not exceed 3,500 kilograms (7,700 lb).

Rob Driver · Guru

The interpretation changes again when we hitch up a 5th Wheeler or even a trailer with a dolly will produce different figures.
As has been mentioned it will depend on the weight of the trailer being under 3500kg.

Peter_n_Margaret · Guru

The requirements of a tow bar are that it can withstand a forward or back (longitudinal) load of 1.5 x its tow rating. That is 5.25T for a tow rating of 3.5T.
The transverse load it must withstand (up, down and sideways) is 50% of its rating. That is 1.75T for a tow rating of 3.5T.
That is the Australian Standard.
Those loads are way beyond what the back ends of many vehicles can withstand. Hence, they get reduced tow capacity ratings.
Cheers,
Peter

yobarr · Guru

To help those who seem to have little understanding of physics, and have difficulty accepting my advice that, if safety is of any concern, always the towing vehicle (car) should be heavier than the towed vehicle (van) I will post this explanation. Most experts suggest that the car should be 10% heavier than the van it is towing, while others, some with over 60 years experience in weights and dynamics,suggest that this figure should be 20% or more. Way back in 1921, Fruehauf, a now world wide heavy trailer manufacturer, worked out that always the tow vehicle must be at least as heavy as the trailer it is towing, thus minimising yaw, or the "tail wagging the dog". Simple physics at work really, but if those who cannot understand the simple physics involved feel so inclined, perhaps they could contact Fruehauf direct and point out they too are "full of lets say 'hot air' ?".Cheers

P.S Please understand that this example refers to PIG trailers, and the same rules do not in any way apply to DOG trailers where a 20 ton prime mover easily and safely tows over 180 ton of laden trailers in NW WA. The truck I drive is a relatively lightweight model, where I tow around 140 ton. Cheers

-- Edited by yobarr on Tuesday 22nd of March 2022 10:39:53 PM

yobarr · Guru

Hi oldbloke,

I think the biggest problem we are forced to recognise is that from that burst of *hot air* we are all towing vans weighing 3.5 tonne with a mid size ute and with 350 kg on the tow bar and that is before anyone uses a WDH.

In the real world there are so many towing vans that are a lot lighter in weight than what may be the maximum allowable figure.

Whilst there certainly are some people towing vans that are below the rated towing capacity of their car, my extensive travels have shown that there are a darn sight more who are towing vans that are way too heavy for the car. When challenged,they usually waffle on about "Yeah,I know we're overloaded, but I drive to the conditions mate".

86GTS · Guru

Fully loaded, my tug weighs twice as much as my caravan (1650kg).
Thats the way I like it.
No tail wagging this dog.
Towing capacities are random figures posted by manufacturers to attract/satisfy potential buyers.
Try disproving them in court if you have a prang.

Whenarewethere · Guru

A bit tail heavy for my liking!

Tiguan 132tsi (2L petrol)

1665 unladen

2260 GVM

2500 towing

100 towball download

Hitting the road · Senior Member

" Vehicles can operate under license which could throw threr argument out the door,

Ie, you see those trucks towing quad axle dog trailers, rough figures truck 22.5 tonnes, the quad dog 30 tonnes operating on a license, a piecie of paper."

...trucks are strictly limited by the manufacturers GVM and GCM and legal axle load capacities as to what they can carry or tow. Most 6x4 tippers you will see have "6 wheel" dogs behind them due to their limitation of their GVM and GCM.

On that basis a 6x4 tipper for example has the capacity to actually load 10 - 11 tonnes of product at the usual GVM of 22.5 tonnes, tare is commonly around 11 tonnes. But, then they are limited by the rear tandem axle legal carrying capacity of 16.5 tonnes and a steer axle legal loading capacity of 6.5 tonnes...giving a total legal load carrying capacity of 23 tonnes less tare of say 11 tonnes = legal payload in fact 11 tonnes. ( the rear axle loading can by increased by up to a tonne with permits)

Truck manufacturers also design a truck where it must have the capacity to move on a minimum gradient at its designated maximum GCM..I can't recall what that gradient is...maybe 3% or something similar.

On the East Coast there are strict limitations on axle capacities related to GCM's. Hence very few trucks and dogs are 6x4 or 8x4 with 8 wheel (quad) dogs behind them, mainly 6x4 with 6 wheel dogs, as the overall Tare weight increases at the expense of reduced payload. Axle loadings coupled with GCM determine legal load. WA is different in that Axle capacity determines loading, therefore 8x4's with 8 wheel (quad) dogs are more common.

Other than that, trucks have a very large part of their load over the drive axle so are far less subject to sway instigated by the trailer. A car towing a van does not have much additional weight over the drive axle when towing or loaded.

I have sold and specced up trucks over the years, and also driven many thousands of kms in heavy vehicles of all sorts and experienced few dramas.

Having also done many of those kms driving road trains pulling up to 3 loaded trailers...combined weight of up to 110 tonnes...then the Prime Mover weighs only maybe 15 tonnes full of fuel, but, there is always load on the drive so you have at least 16.5 tonnes on the 8 tyres contacting the road. A driver is pretty confident that he will have traction in most scenarios...unlike a normal motor vehicle where the contact patch is very small for the additional weights imposed.

Hence my comment that I wouldn't be comfortable at all in a dual cab ute weight 2500kg towing a trailer weighing 3500kg as there is zero additional weight (maybe 300kg) on the drive to assist stability and traction...

Peter_n_Margaret · Guru

Hitting the road wrote:
Truck manufacturers also design a truck where it must have the capacity to move on a minimum gradient at its designated maximum GCM..I can't recall what that gradient is...maybe 3% or something similar.

While loaded to GCM, a vehicle must be able to pull away from stationary on a 12% slope and continue to drive up a 20% slope.

I had a GCM increase on the OKA from 7T to 9T and that was the criteria.

Cheers,

Peter

yobarr · Guru

Peter_n_Margaret wrote:
Hitting the road wrote:
Truck manufacturers also design a truck where it must have the capacity to move on a minimum gradient at its designated maximum GCM..I can't recall what that gradient is...maybe 3% or something similar.
While loaded to GCM, a vehicle must be able to pull away from stationary on a 12% slope and continue to drive up a 20% slope.
I had a GCM increase on the OKA from 7T to 9T and that was the criteria.
Cheers,
Peter

Thanks Peter. Because I knew that you are aware of how a tow rating is issued, I was waiting for your explanation to appear. You may remember that we discussed this some time ago, and I have actually posted the process several times since, in general discussions about weights. Thanks again. Cheers

Gundog · Guru

One wonders where these so called rules, like towball weight must be 10% or greater, and towing vehicle must be heavier than the trailer are published. Because for the life of me I cannot find them anywhere, except for opinions by so called xspurts.

Here's a little a little knotty problem for you to resolve, my Ford Ranger has a towing capacity 3000kg a GCM of 5500kg, my Ford towbar is rated at 3000kg with a maximum ball weight of 250kg ( I raised the issue with Ford Australia the reason for lower ball weight is because the Automatic Transmission version of my model has a 2500kg towing capacity). I then approached a popular towbar manufacture about the specs of their towbar pointing out the issue with Ford product, they advised they supply a HD towhitch rated at 3000kg/300kg.

When I started my grey nomad adventure 7 years ago my GCM was bang on 5500kg ball weight was 240kg approximatly 9% of caravan which was 200kg heavies than the Ranger, fast forward a few years, Ranger and Jayco are about equal weight. Over the entire time wether from day one to now have I ever encounterd the tail wagging the dog or felt unsafe.

WARNING * My model Ranger requires the a WDH be used when towing in excess of 1800kg *

Could this be part of the reason I have not encounered a problem, a correctly fitted and applied weight distribution hitch.

-- Edited by Gundog on Wednesday 23rd of March 2022 11:41:03 AM

yobarr · Guru

Hitting the road wrote:
" Vehicles can operate under license which could throw threr argument out the door,
Ie, you see those trucks towing quad axle dog trailers, rough figures truck 22.5 tonnes, the quad dog 30 tonnes operating on a license, a piecie of paper."

...trucks are strictly limited by the manufacturers GVM and GCM and legal axle load capacities as to what they can carry or tow. Most 6x4 tippers you will see have "6 wheel" dogs behind them due to their limitation of their GVM and GCM.
On that basis a 6x4 tipper for example has the capacity to actually load 10 - 11 tonnes of product at the usual GVM of 22.5 tonnes, tare is commonly around 11 tonnes. But, then they are limited by the rear tandem axle legal carrying capacity of 16.5 tonnes and a steer axle legal loading capacity of 6.5 tonnes...giving a total legal load carrying capacity of 23 tonnes less tare of say 11 tonnes = legal payload in fact 11 tonnes. ( the rear axle loading can by increased by up to a tonne with permits)
Truck manufacturers also design a truck where it must have the capacity to move on a minimum gradient at its designated maximum GCM..I can't recall what that gradient is...maybe 3% or something similar.
On the East Coast there are strict limitations on axle capacities related to GCM's. Hence very few trucks and dogs are 6x4 or 8x4 with 8 wheel (quad) dogs behind them, mainly 6x4 with 6 wheel dogs, as the overall Tare weight increases at the expense of reduced payload. Axle loadings coupled with GCM determine legal load. WA is different in that Axle capacity determines loading, therefore 8x4's with 8 wheel (quad) dogs are more common.
Other than that, trucks have a very large part of their load over the drive axle so are far less subject to sway instigated by the trailer. A car towing a van does not have much additional weight over the drive axle when towing or loaded.
I have sold and specced up trucks over the years, and also driven many thousands of kms in heavy vehicles of all sorts and experienced few dramas.
Having also done many of those kms driving road trains pulling up to 3 loaded trailers...combined weight of up to 110 tonnes...then the Prime Mover weighs only maybe 15 tonnes full of fuel, but, there is always load on the drive so you have at least 16.5 tonnes on the 8 tyres contacting the road. A driver is pretty confident that he will have traction in most scenarios...unlike a normal motor vehicle where the contact patch is very small for the additional weights imposed.
Hence my comment that I wouldn't be comfortable at all in a dual cab ute 2500kg towing a trailer weighing 3500kg as there is zero additional weight (maybe 300kg) on the drive to assist stability and traction...

Great post Dean, which shows that you have a great understanding of weights and dynamics, gained from your personal experience and a greater understanding of basic physics. Let's hope that this is of some assistance to those who seem to not be able to understand why "tail wagging the dog" is minimised by having the tow vehicle (car?) heavier than the towed vehicle (van). Keep up the good work! Cheers

-- Edited by yobarr on Wednesday 23rd of March 2022 01:53:02 PM

Peter_n_Margaret · Guru

Gundog wrote:
One wonders where these so called rules, like towball weight must be 10% or greater, and towing vehicle must be heavier than the trailer are published.

They are NOT "rules". They are conventions, and mostly in Australia, not other places.

In Europe, 5% is a more typical ball weight, but they don't have heavy front and rear ends to their vans so their yaw inertia is much more sensible that is typical here.

When I tow our off road trailer (which can weigh 2T) behind the OKA, I would typically have a ball weight of about 20kg. That is 1%. It has a long draw bar and low yaw inertia and the OKA weighs about 6T.

Cheers,

Peter

-- Edited by Peter_n_Margaret on Wednesday 23rd of March 2022 01:50:03 PM