Upgrading GVM or GCM

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 .

John,
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

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.

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.

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
and
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.

DD

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.

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

Deifintely NOT, NEVER, FORGET IT.

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.

RING YOUR OWN STATE AUTHORITY

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

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’