Upgrading GVM or GCM

Submitted: Sunday, Mar 06, 2011 at 20:28
ThreadID: 84837 Views:11199 Replies:7 FollowUps:10
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Hi! Does anyone know if you can up grade your GCM? I posted a thread the other day talking about GVM upgrades, but if you do that it lessens what weight you can tow. Someone came back with a reply from WA saying that his mate had his done and the engineer gave him the choice of upgrading GVM or GCM. If you can upgrade your GVM, the amount it was increased should be added to the GCM. My thoughts anyway!! If you only get the choice to upgrade one of them, which would be the better to upgrade when towing heavy kedron van around oz? Cheers. John
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Reply By: Snoopyone - Sunday, Mar 06, 2011 at 20:46

Sunday, Mar 06, 2011 at 20:46
I have posted a thread on Lcool about it but had no replies yet.

The best advice is ring the relevant authority in your state.

As you see the advice I gave has been contradicted and tomorrow I intend ringing an specialist in QLD Roads about it..

Every thread I have seen says you cant uprate GCVM.

It would put a lot of added strain on all components with the added weight in the tug.

The manufacturers GCVM is a well thought out figure addressing the limitations of the vehicle .

AnswerID: 447497

Reply By: Rockape - Sunday, Mar 06, 2011 at 20:49

Sunday, Mar 06, 2011 at 20:49
this may help.

On-Vehicle Capacity
GVM - Gross Vehicle Mass
Gross Vehicle Mass is the accepted safe, maximum allowable total mass of a fully loaded motor vehicle. It consists of the kerb mass (mass of the vehicle itself with all operating fluids) plus the payload

A vehicles’ payload is the maximum capacity of the vehicle for the transport of all non-standard items including the vehicles body (tray, tipper, van etc), the cargo itself, occupants and optional equipment and accessories (bull bars, spot lights, roof racks, tow bars etc)

Kerb Mass
A vehicles kerb mass is the mass of the vehicle in running order, unoccupied and unladen with all fluid reservoirs filled to their nominated capacity. All standard vehicle equipment is also included in the kerb mass.

Maximum Available Payload
The available payload is calculated by subtracting from the vehicles GVM, the vehicles kerb mass, the total weight of the occupants, the weight of any fitted options (bull bar, tow bar, spot lights etc) and the weight of the fitted body (tray, van, tipper). This remaining figure is the maximum allowable weight of the cargo which is to be placed upon the vehicle. Calculate your maximum allowable payload.

Axle Weights
The final point of interest in vehicle weight determination is axle weights. The axle weight is the maximum load that can be placed over each axle on the vehicle. Each vehicle will normally specify their front and rear axle weight in the product specification sheet.

In some vehicles the rear axle is not rated sufficiently to take the entire weight of the payload by itself. In these instances some weight will need to be re-distributed over the front axle, this is commonly done by using a rack arrangement. Be sure to check your individual vehicles specification sheet to ensure that your payload can be supported on the desired areas of the vehicle.

Towing Capacity
Calculating the towing capacity is relatively straight forward once you have calculated your maximum allowable payload.
Maximum towing capacity
Each vehicle will have a maximum towing capacity with braked an un-braked trailers. This is the total weight the vehicle can legally tow and it includes the physical weight of the trailer as well as the weight of the cargo placed upon it.

Things can become complicated when a vehicle, which can tow a given amount when unladen, attempts to tow a trailer with payload weight also on the body. It does not matter if the vehicle can tow a given weight in a particular situation; it cannot, at any time, exceed its nominated GCM.

GCM - Gross Combination Mass
Gross Combination Mass is the accepted safe, maximum allowable total mass of a fully loaded motor vehicle and all of its trailers.

Mate, this is just a copy and paste and simple explanation is, if your vehicle compliance plate says you can tow 2500kg, then it doesn't matter whether you upgrade your gvm or not you still can't tow more than 2500kg. What you can do is have more downforce on your drawbar (if it is rated for more) or more weight in the vehicle until you reach your gvm.

Have a good one.

AnswerID: 447500

Reply By: fisho64 - Sunday, Mar 06, 2011 at 21:57

Sunday, Mar 06, 2011 at 21:57
I spoke to the DOT WA transport guys about increasing the tow limit of my old Hilux (1500 to 1800). They told me it CANNOT be done, even if you keep the GCM the same which doesnt make sense to me. They were telling me that the vehicle manufacturers set the maximum due to the vehicles construction, brakes etc. I wanted to increase the tow by 300kg and the lessen the payload by the same but they said "cannot be done". I dont understand as the brakes will still be stopping a maximum (GCM) unchanged.
AnswerID: 447515

Reply By: Dust-Devil - Sunday, Mar 06, 2011 at 23:18

Sunday, Mar 06, 2011 at 23:18
John P

You can change/re-engineer anything you like on a vehicle if you have the MONEY, time and patience to do so.

In October 2005 I had the GVM of my 1997 75 series Troopy re-engineered from 3100kgs to 3495kgs.

The engineering certificate shows:

Original Specs 1400kgs front axle, 2000kgs rear axle - GCVM 6350kgs
Re-eng'd Specs. 1400kgs front axle, 2500kgs rear axle - GCVM 6350kgs

The maximum a 75 series Toyota GVM can be upgraded to is 3500kgs before you have to add a ridiculous amount of emission control gear, plus arduous testing programme, that makes it totally cost prohibitive to do so. The Engineer said at the time that it would be cheaper to buy two new Troopys.

With this in mind he took the upgrade to 3495kgs so that it was just under the magical 3500kg mark so that there would be no arguments.

You will notice that the GCVM did not change during the aforementioned exercise
However what did also change was the Tyre Placard which increased tyre size specs a tad.

This is just a snapshot of what was done re GVM upgrade. How it was done is another long and involved story which I'm not going into. It was done in Victoria and all States have their own idiosyncrasies as to how they do this stuff.

Engineering computations - The Engineer had a book the size of the old Encyclopaedia Britannica, which had all the engineering specs for the original vehicle build ( Brakes, springs, shackles, Shockers, wheels, tyres, axles, chassis etc etc) which were entered into a computer program along with all his vehicle test results, and bingo there you have it.

AnswerID: 447524

Reply By: JR - Monday, Mar 07, 2011 at 09:03

Monday, Mar 07, 2011 at 09:03
Im pretty sure only trucks >3T have GCM.
Light vehicles have GVM and Max Towable. Of course if you add them theres effectively the GCM but legally it doesnt exist.
Max towable is set by manufacturer and near impossible to alter except downwards.
GVM can be uprated but only with engineers approval, he may request structural upgrades, braking, swerve tests plus his fees etc (read as mega $$$)
The engineer can allow for Max tow downgrade and GVM upgrade so long as he reckons vehicle can handle it, he'd be very brave to say this if it exceeds max axle capacities. Id be suprised if any of them would permit increase in GVM whilst leaving Max tow the same without serious upgrades to vehicle.
Rules on changes are set by states though so its different each one so watch what you end up with if travelling. ie if certified OK in WA, may not be legal in NSW etc.
AnswerID: 447538

Follow Up By: Snoopyone - Monday, Mar 07, 2011 at 09:22

Monday, Mar 07, 2011 at 09:22
From Toyota 100Td Auto specs

Kerb weight 2588kg

Payload 672kg

GVM 3260kg

GCM 6680kg

Roofrack 200kg

Max towed weight 3500kg

Subject to local rules regarding towbars etc

FollowupID: 719828

Reply By: Snoopyone - Monday, Mar 07, 2011 at 12:53

Monday, Mar 07, 2011 at 12:53
Ok I have just got off the phone to a specialist in the Queensland Dept of Roads

Heres what he said

Firstly towing weights.

Its the ATM that matters and both may not exceed the rated GCVM

Secondly upgrades of GVM.

In Queensland can only be done by second level manufacturers and preferably before vehicle is first registered.
Can be done later but ??????? and only by the same people who have a Federal licence. EG Lovells or similar who are licensed to do this

Upgrade of GCVM


In contrast to the towing weights New South Wales RTA say its the GTM that matters so where are we ????????????????????????????????

I said to him about the WA post above and he said engineers may interpret regulation in correctly but as far as he knows no one anywhere can legally uprate your GCVM and they need the qualification as above for GVM.

This gets you a different plate to the blue plate for mods like removing seats etc.

HE also said dont ask on forums and get told all sorts of things.


I totally agree and have just posted this as a help although I guess it came from a totally reliable source.

AnswerID: 447560

Follow Up By: Snoopyone - Wednesday, Mar 09, 2011 at 11:15

Wednesday, Mar 09, 2011 at 11:15
I asked the question at TOYOTA AUSTRALIA and the answer I got is

Toyota do not have published GCVM figures for their vehicles

The man said that yes you can get your GVM upgraded if done by the correctly licensed operators

Like Lovells.


So according to him you can still tow the 3500kg.

However he did say that it will put an additional strain on all drive train

components and probably shorten the life of the vehicle.

He laughed and said he likes selling parts and if you want to help him fire away.

HE also said Forums are the worst place for getting advice and he is constantly amused by replies on them.

Which brings us to the differences between QLD And NSW

QLD say its the ATM that matters when taking towing weight NSW say its the GTM

I cant publish the reply from QLD but what it says is that if a vehicle has a published GCM you cannot exceed it

If it doesnt you can as said above by the Toyota person.

Which is all very helpful except there does not seem to be a national standard for this.

I also mentioned to the QLD guy about things like Pillar Pods for gauges which are apparently banned in NSW.

He said if they intrude on your vision they are in QLD as well and that includes navigators planted in the middle of windscreens at eye height

The ADR rules have settings for limitations of things that intrude on vision above the bonnet line which include aerials of a diameter of more than 75mm Spotlights above a certain height etc.

Have fun folks.

FollowupID: 720056

Reply By: The Landy - Monday, Mar 07, 2011 at 14:39

Monday, Mar 07, 2011 at 14:39
I’m genuinely interested to know why people need to increase the GVM of a vehicle. I’ve often seen this question and formed a view, perhaps incorrectly, that if you can’t carry what you need within the manufacturer’s GVM limit then you are either carrying too much gear, or have the wrong vehicle for your requirements.

Just interested, and wish you luck with getting the changes you need.

Cheers, ‘The Landy’
AnswerID: 447575

Follow Up By: Snoopyone - Monday, Mar 07, 2011 at 14:56

Monday, Mar 07, 2011 at 14:56
Usually because they load all the fruit like Steel bars and a winch, dual

wheel carriers, a long range tank and then no weight allowance left for Mum , the

kids and lunch even. Never mind the ballweight of the van.

Most popular 4b's have a serious deficiency in the amount of payload they have.

FollowupID: 719866

Follow Up By: disco driver - Monday, Mar 07, 2011 at 19:14

Monday, Mar 07, 2011 at 19:14
Most people,as you say, load their vehicle up with heap of 'just in case'gear and then try to pack enough clothes and food for a month rather than having to do a load or two of washing somewhere or buy a bit of tucker from the small towns they pass through.
There's no problem with the vehicles it's just that people ask too much of them in standard set-up.
Buy a bloody 4wd truck instead.

FollowupID: 719904

Follow Up By: CSeaJay - Monday, Mar 07, 2011 at 21:25

Monday, Mar 07, 2011 at 21:25

I disagree with Disco as it is a generalised statement. Fact is with most large 4wd's, you only have so much weight to play with , and by the time you fill up with fuel, jerries/longrange, water, extra spare, and with four people in it, you are at or close to GVM. The above are not packing enough for a month, it is often a minimum requirement for crossing a desert like Simpson (CSR even worse)
FollowupID: 719938

Follow Up By: Snoopyone - Monday, Mar 07, 2011 at 21:53

Monday, Mar 07, 2011 at 21:53
I agree with you take the 100ser which has 672kg payload

275 for ballweight brings it back to 397

You and mum say 150kg leaves 247.

You have put a steel bar on and a winch so there goes another 100kg leaves 147kg

You put a roof rack on which is over 50kg UNLOADED leaves 97kg for tools, extra fuel, any kids, a gennie, a set of drawers and a fridge and any load on the rack.

I maintain they are not designed for the usage that we expect from them and as we are a small part of the total sales in the world they will never reconfigure them to suit our conditions.

Even without the van on it may be hard to stay legal and yet we see them loaded up to the hilt with a tinnie on the top with an outboard as well and loaded up to the gunwales in the back with a 3000kg van on the back.

Get real folks.

FollowupID: 719942

Follow Up By: The Landy - Tuesday, Mar 08, 2011 at 09:31

Tuesday, Mar 08, 2011 at 09:31
Accepting that Defender’s are not everyone’s cup of tea, but one of the reasons we went the way we did was because of the load capacity of the Defender 130.

If I take the basic empty weight, which includes all modifications such as the canopy, bulbar etc (vehicle as you see it essentially), add 200 litres of fuel, and 70 litres of water, plus two adults and one child, I still have an excess load capacity of just over 500 kgs.

Cheers, The Landy.....

FollowupID: 719961

Follow Up By: farouk - Friday, Mar 11, 2011 at 23:02

Friday, Mar 11, 2011 at 23:02
Sorry guys but there is one state(S .A) where you can get both the GVM and the load capacity of the caravan increased,
Refer to this site


FollowupID: 720309

Follow Up By: Snoopyone - Saturday, Mar 12, 2011 at 08:57

Saturday, Mar 12, 2011 at 08:57
Sorry but you can get what you say done in QLD as well as I have had my first van uprated from 2500kg to 2800kg

As my vehicle was already capable of towing that It didnt need a GVM upgrade done.
I t could have been done as well if needed.

What the question originally was, was can the GCM which is the combined weight of both be increased beyond its rated limit.

Maybe possible but certainly as said by the Toyota rep not very wise.

FollowupID: 720323

Follow Up By: Ron N - Saturday, Apr 02, 2011 at 20:12

Saturday, Apr 02, 2011 at 20:12
Ha! Ha! I can recall organising to go up the CSR with a group of farmers in mid-1989. In the end I never went, because my F100 4WD rebuild wasn't finished in time. However, I remember one of the blokes with a HJ75 traytop, tared out at THREE TONNES, before he even left!!
They took everything but the kitchen sink! They must have thrown in half the farm workshop! Needless to say, they had to do some serious lightening before they left.
As it was, despite taking everything they thought they'd need, one of the 'Cruisers busted a steering knuckle just over halfway up the CSR, and they had to make a dash into Pt Hedland for a replacement!

Re the GVM/GCM increase - you can change anything, if you find a good engineer that specialises in modifications, and he can tell you what you need to upgrade - and then get him to sign off on it.
However, that can be a costly exercise, because most State authorities are very reluctant to allow alterations to manufacturers GVM's and GCM's.
Anythings possible, because you see some wondrous hotrods registered, with some amazing alterations.
However, the trend by State authorities is that they will almost certainly not authorise any modifications done by an owner - it has to be done by a shop/business with a proven track record in vehicle modifications. These are the only people doing modifications, that the State rego authorities will deal with.
FollowupID: 722574

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