Written byGross combination mass (GCM) is the maximum a vehicle and everything it is towing can legally weigh together, as set by the vehicle's manufacturer.
Also known as: GCM, gross combined mass, gross combination mass, GCM rating
Key points
- GCM is usually less than GVM plus the trailer's maximum, so a ute's advertised towing capacity rarely survives a full tray and cabin.
- Tow ball weight counts against the tow vehicle's GVM as well as the GCM, which is what catches most caravan owners out.
- Exceeding GCM is an offence and gives your insurer grounds to decline a claim, so the numbers matter before you buy the van.
- Before the caravan goes on a secured loan alongside the ute's car loan, a weighbridge visit shows whether the pair can legally travel together.
How GCM works
A manufacturer rates each vehicle for the most it can weigh on its own (GVM) and the most the whole rig can weigh with a trailer attached (GCM). Both are on the compliance plate or in the handbook. On the road, the loaded vehicle plus the loaded trailer are measured together, and that total has to sit under the GCM at the same time as the vehicle sits under its GVM and the trailer under its own rating.
The trap is that the three numbers rarely add up neatly. Many popular utes have a GCM that is less than their GVM plus their braked towing capacity, so the advertised towing figure only holds when the vehicle itself is lightly loaded. Every kilogram of gear in the tray comes off what the trailer can weigh.
GCM and caravan buying
The sensible order is to weigh the tow vehicle as it will actually travel, with people, fuel, canopy and gear, then subtract that from the GCM to see how heavy the loaded van can be. The van's aggregate trailer mass, its own maximum when loaded, has to fit inside that gap, and its tow ball weight has to fit inside the ute's remaining GVM. A weight distribution hitch spreads load but changes none of the ratings.
Dealers quote towing capacity; they rarely quote what is left once the family is on board. A public weighbridge visit with the asset you already own, before signing for the one you want, costs a few dollars and answers the question the brochure does not.
GCM, insurance and finance
An overloaded combination is illegal in every state, and if it is involved in a crash the insurer can decline the claim for both the vehicle and the van. Where either is financed, the lender's security is sitting in a vehicle that is not covered, which is a problem for the borrower long before it is one for the lender.
GCM upgrades exist, usually alongside a GVM upgrade, but they are engineered and certified case by case and not every state accepts them for every vehicle. The total cost of ownership of towing at the limit also climbs: fuel, tyres, brakes and transmission all wear faster, and a combination that is comfortably inside its GCM is cheaper to run as well as legal.
Example
A couple in Wagga Wagga finance a family caravan and plan to tow it with their existing dual-cab. Before the first trip they drive both to a weighbridge with the tanks full and the tray packed. The ute on its own is under its GVM, and the van is under its rating, but together they are over the GCM, with the tow ball weight also pushing the ute close to its limit. They shed the second spare, move the water to the van's tanks for travel days only, and reweigh. The combination now sits under GCM with margin to spare, and an insurer would have no grounds to refuse a claim.
Not to be confused with
- Gross vehicle mass (GVM)
- gross vehicle mass caps the vehicle on its own, while GCM caps the vehicle and trailer together
Frequently asked questions
What is the difference between GVM and GCM?
GVM is the maximum the vehicle alone may weigh when loaded. GCM is the maximum the vehicle and its trailer may weigh together. A loaded ute has to be under its GVM, the trailer under its rating, and the two combined under the GCM, all at the same time. GCM is usually less than the sum of the other two.
How do I find my car's GCM?
On the compliance plate, in the owner's handbook or on the manufacturer's specification sheet for your exact model and variant, since it can differ between engines and body styles. If the vehicle has had a GVM or GCM upgrade, the new figure is on the additional plate the engineer fitted. Registration papers usually show GVM but not GCM.
Can I upgrade my vehicle's GCM?
Sometimes. GCM upgrades are engineered and certified individually, often together with a GVM upgrade, and state rules on whether they are recognised, and for which vehicles, are not uniform. Some manufacturers refuse to warrant them. Two things are worth confirming before paying for one: that your state's registration authority accepts it, and that your insurer will cover the upgraded vehicle.
Does towing capacity equal GCM?
No. Towing capacity is the heaviest trailer the vehicle is rated to pull. GCM is the ceiling for the vehicle and trailer combined. If the loaded vehicle plus a trailer at full towing capacity would exceed the GCM, the real limit is lower than the advertised towing figure, and it drops further as the vehicle is loaded.
What happens if I tow over the GCM?
You are driving an overloaded combination, which attracts fines and, in a crash, gives the insurer grounds to refuse the claim on both the vehicle and the trailer. Handling, braking and stability all suffer, which is why the ratings exist. Roadside weight checks are common on caravan routes, and the onus is on the driver to know the numbers.
Related terms
Gross vehicle mass (GVM)
Gross vehicle mass (GVM) is the maximum a vehicle can legally weigh when fully loaded, including fuel, passengers, accessories and cargo, as set by the manufacturer.
Read definitionCar loan
A car loan is a credit contract used to buy a vehicle: the lender provides the funds and you repay them over time with interest.
Read definitionComprehensive car insurance
Comprehensive car insurance is the broadest level of motor cover, paying for damage to your own car as well as damage you cause to other people's property.
Read definitionTotal cost of ownership (TCO)
Total cost of ownership (TCO) is the full cost of buying, financing, running and disposing of an asset over a set period, not just its purchase price.
Read definitionAsset
An asset is anything a business or person owns or controls that is expected to produce future economic benefit, such as cash, equipment, vehicles, property or receivables.
Read definitionInsurance
Insurance is a contract where you pay a premium and an insurer covers specified losses, such as damage to a financed asset or a lender's loss on default.
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Sources
This article is general information only and is not financial advice.