THE MAGAZINE HAS GOT IT WRONG

[chrissmith61]

With all the talk about towing capacity of modern day cars and utes and being overweight I was looking forward to reading the article on towing 3.5 tonne in the new Caravan and Motorhome on Tour magazine.

I came to the "Glossary of Terms" on the left column on Page 83.
Firstly there is no mention of (GTM) Gross Trailer Mass.
Then the explanation of Gross Combined Mass(GCM). It says that GVM + ATM = ATM. THis is blatantly wrong.

GVM + GTM = GCM.

No wonder there is so many arguments on these Forums and around the campfire if the "Experts" get it wrong.

I have been compiling my own page about weights on my blog for a little while now. While it is not all my own work, I have been compiling a lot of revelant information for interested people to browse through.
https://chrisanddiannesultimaadventure. ... explained/

I would love to here what the magazine hierarchy have to say before I post it on some other forums.

[TramcarTrev]

Who is the author of the article? If it's a paid expert then Candy can claim that it's not their problem.
However all this does is discredit the editor who's job it is to ensure accuracy of any material in the mag.
Personally I think I'd be taking a careful look at my team to ensure they had the qualifications to do the job. I've seen articles showing how to something that have been totally incorrect yet no one on the editorial team has the expertise to correct.

[Old Techo]

With all the talk about towing capacity of modern day cars and utes and being overweight I was looking forward to reading the article on towing 3.5 tonne in the new Caravan and Motorhome on Tour magazine.

What Mag number please Chris?

I get hand-me-downs and the latest is #239

[chrissmith61]

Issue 240 Old Techo, I only got mine today in the mail and it was the first article I read

[Motherhen]

So many times I read articles published that make errors and confuse newbies. For that reason I put the basic terms in plain English (girl speak) on my website. While in the case it is probably a typo, magazine articles are edited by editors, not technical experts in the field. This often means technical stuff does not make sense or is plain wrong. Sometime is it just perpetuating a myth such as mixing maximum allowable measurements and actually loaded measurement, and expecting to get a meaningful measurement.

[Old Techo]

I came to the "Glossary of Terms" on the left column on Page 83.
Firstly there is no mention of (GTM) Gross Trailer Mass.
Then the explanation of Gross Combined Mass(GCM). It says that GVM + ATM = ATM. THis is blatantly wrong.

GVM + GTM = GCM.

No wonder there is so many arguments on these Forums and around the campfire if the "Experts" get it wrong.

G'day Chris and thanks for the Mag number. I got my hands on one today.

Now I understand campfire arguments. I've never before bothered to considered this matter. My head has been spinning for an hour or so

I think both you and the Mag can be right depending upon your perspective. By the way, you have a typo when you quoted the Mag as GVM + ATM = ATM.

If I sent you to a weighbridge to get a single mass value for an entire rig that would be measuring the actual GCM. If you claimed that the GCM comprised the sum of the GVM and the GTM then you would be right if when I moved payload within the van, thus reducing the ball-weight, that you adjusted both the GVM value and the GTM value as both will change as I relocate mass rearwards within the van. The tug GVM drops and the van GTM increases whereas the ATM is unchanged.

Does the difficulty not arise when the GVM in reality is a legally fixed value, quite independent of actual load. It is a maker's sort-of theoretical spec. It may say the GVM is 3000 kg and this will be whether empty or full of payload. It is merely a number not to be exceeded. Thus with a fixed GVM of 3000 kg (irrespective of actual loaded state) it would be correct to state that when a trailer is connected to the tug it is the trailer ATM that should be added to the equation.

The 2 perspectives I am trying to explain are (1) what the law states i.e. these are maker-set theoretical limits (viewpoint from the maker's engineer) and (2) what one measures in practice (viewpoint of a curious owner at the weighbridge). The maker may say GVM is 3000 kg and the ATM is 2000 kg but when you get to the weighbridge you individually measure your separated tug and van and get an in-practice tug figure of 2700 kg (GVM) and a van figure of 1800 kg ( ATM) and then you may rightly claim your GCM as measured will be GVM + ATM. Is this perhaps the Mag perspective?

[chrissmith61]

I came to the "Glossary of Terms" on the left column on Page 83.
Firstly there is no mention of (GTM) Gross Trailer Mass.
Then the explanation of Gross Combined Mass(GCM). It says that GVM + ATM = GCM. This is has been corrected.

GVM + GTM = GCM.

No wonder there is so many arguments on these Forums and around the campfire if the "Experts" get it wrong.

G'day Chris and thanks for the Mag number. I got my hands on one today.

Now I understand campfire arguments. I've never before bothered to considered this matter. My head has been spinning for an hour or so

I think both you and the Mag can be right depending upon your perspective. By the way, you have a typo when you quoted the Mag as GVM + ATM = ATM.

If I sent you to a weighbridge to get a single mass value for an entire rig that would be measuring the actual GCM. If you claimed that the GCM comprised the sum of the GVM and the GTM then you would be right if when I moved payload within the van, thus reducing the ball-weight, that you adjusted both the GVM value and the GTM value as both will change as I relocate mass rearwards within the van. The tug GVM drops and the van GTM increases whereas the ATM is unchanged.

Does the difficulty not arise when the GVM in reality is a legally fixed value, quite independent of actual load. It is a maker's sort-of theoretical spec. It may say the GVM is 3000 kg and this will be whether empty or full of payload. It is merely a number not to be exceeded. Thus with a fixed GVM of 3000 kg (irrespective of actual loaded state) it would be correct to state that when a trailer is connected to the tug it is the trailer ATM that should be added to the equation.

The 2 perspectives I am trying to explain are (1) what the law states i.e. these are maker-set theoretical limits (viewpoint from the maker's engineer) and (2) what one measures in practice (viewpoint of a curious owner at the weighbridge). The maker may say GVM is 3000 kg and the ATM is 2000 kg but when you get to the weighbridge you individually measure your separated tug and van and get an in-practice tug figure of 2700 kg (GVM) and a van figure of 1800 kg ( ATM) and then you may rightly claim your GCM as measured will be GVM + ATM. Is this perhaps the Mag perspective?

Hi Old Techo, I found my mistake, that is how easy 2 letters can mess up a whole story and give the wrong message. I can't go back and edit it out.

The magazine has quoted "GVM + ATM = GCM" at the bottom of column one on page 83.

The correct formula should be "GVM + GTM = GCM"

You said above

If I sent you to a weighbridge to get a single mass value for an entire rig that would be measuring the actual GCM
You would be measuring the actual weight. This must be under the GCM

You then added

If you claimed that the GCM comprised the sum of the GVM and the GTM then you would be right if when I moved payload within the van, thus reducing the ball-weight, that you adjusted both the GVM value and the GTM value as both will change as I relocate mass rearwards within the van. The tug GVM drops and the van GTM increases whereas the ATM is unchanged.
The GVM and GTM don't change, the weights may change over each axle group. You must remain under the rated GVM and GTM values

You also said

Does the difficulty not arise when the GVM in reality is a legally fixed value, quite independent of actual load. It is a maker's sort-of theoretical spec. It may say the GVM is 3000 kg
The GVM is a specifcation and the legal maximum limit. It is not to be exceeded.
Your weight can be less.

At the end of the day

The weight on the tow vehicle axles when hooked up ready to go and the weight on the caravan axles must be less than the GCM rating of the tow vehicle

[TramcarTrev]

At the end of the day the average man in the street has no idea about all the acronyms re vehicle weights.

Tactically all they need to know is that they do not exceed the maximum load for their vehicle, This is the maximum your vehicle can weigh when fully loaded as specified by the manufacturer. You will usually find this GVM figure on the vehicle's weight placard (generally found in the driver's door opening) or in the owner's manual. So Gross Vehicle Mass/Weight is the weight plus driver, passengers, luggage, pet dog, esky, tool kit and whatever else you're taking with you. And if you're towing something, Gross Vehicle Mass/Weight also includes the Tow Ball Download.

Tow Bar Download (TBD) is the amount of weight on your tow bar is crucial to safe and efficient towing and needs to be mentioned here. Any quality tow bar will have a placard or similar showing the maximum tow bar capacity (kg) and maximum tow bar download (kg). Make sure the tow bar you choose is designed specifically to suit your vehicle and your towing capacity requirements.

Typically the TBD should also be around 10-15 percent of the Gross Trailer Mass (GTM), which for peace of mind can also be calculated using the GTM and TBD figures as shown here: TBD divided by GTM x 100 = % of GTM.

They also need to know the Aggregate Trailer Mass (ATM) or Weight (ATW)
This is the Gross Trailer Mass (GTM) plus the Tow Bar Download . In other words, the ATM is the maximum towing weight of the trailer/caravan as specified by the manufacturer.

Thats about as simple as it gets....

[Old Techo]

Thanks Chris, but you are limiting the conversation to my perspective (1).

The Oxford Dictionary describes gross the following way....

(of weight) including contents, wrappings, or other variable items; overall:
‘a projected gross take-off weight of 500,000 pounds’

In my perspective (2) what I measure on the weighbridge is my actual mass and it is proper to call it gross vehicle mass as defined by Oxford. So this is the 'other' and practical perspective.

Rather than having to explain that I weighed my vehicle at 2700 kg when it was full of fuel, luggage, tools, spares, people and the dog, ready for the road - it is simpler and correct to say it had a gross mass of 2700 kg. The important bit is that my measured GVM does not exceed the maker's stipulated GVM.

All I am suggesting is there exists a valid use of the term (in conversation) that is different to a maker's spec and perhaps this contributes to campfire arguments

[chrissmith61]

Old Techo said
"The important bit is that my measured GVM does not exceed the maker's stipulated GVM."

This would include any ballweight when hooked up ready go.
Then to stay under your GCM you would add your total vechile mass and the measured mass on your caravan wheels, your GTM