There’s been a bit of a hoo-ha around GCM and GVM in the world of 4WD and towing lately, including the recent announcement of the decision by the South Australian Government to reverse their ban on the installation of after market towing upgrades by certified Second Stage Manufacturers.
But what do GCM and GVM actually mean? What about towing capacity and GTM? What can I do about it and what are the consequences if I don’t do anything?
Note: The following is designed to be a guide only. Please contact the experts at TJM and they will talk you through your particular situation.
GVM (Gross Vehicle Mass)
The Gross Vehicle Mass (GVM) is the maximum your vehicle can weigh and is specified by your car’s manufacturer – you’ll usually find this in the plaque in the driver’s door-well, or in your owner’s manual. The weight indicated includes everything in and on your vehicle … you, your passengers, bullbar, tools, fridge, luggage, fishing gear, kitchen sink … as well as your tow ball weight.
Tip: know what your kerb weight is! Your kerb weight is what your vehicle weighs when it’s empty and in its ‘brand new’ state with no additions. If your vehicle weighs in at 2000kg and your GVM is 3200kg, then you know you’ve got 1200kg of load up your sleeve when you start adding accessories and fittings, but remember the more you add here, the less you can tow (read on to find out why).
This number is the maximum weight that your vehicle is recommended to tow and is specified by the manufacturers according to their engineering approvals. To complicate things, this capacity is dependant on the rating of your towbar; if your vehicle is rated to tow 3500kg but your towbar is only rated 2500kg, then you should go by the lower number.
GCM (Gross Combination Mass)
The Gross Combination Mass (GCM) is the maximum that everything can weigh. Once upon a time your GCM was simply calculated by adding your vehicle’s GVM to its towing capacity. Not anymore! Manufacturers are now specifying what your GCM is and it’s what the authorities are using to determine if you’re over the limit or not! This critical number can also be found in the driver’s side door-well.
GTM (Gross Trailer Mass)
The maximum your trailer can weigh fully laden with any gear, water, gas bottles, annexe etc. This will be specified by your trailer manufacturer.
An (almost) real-life scenario
John and Judy are about to take to the road with their two children. They’ve bought an SUV and are going to kit it out with a bunch of items to make their trip more comfortable and enjoyable and their vehicle more efficient and safe.
Their setup has the following details:
Kerb Weight: 2111kg
Towing Capacity (towbar rating): 3500kg
*Note that the vehicle manufacturer has specified a GCM that is 700kg less than the sum of the GVM and Towing Capacity!
John has decided to add a bullbar, winch, a long-range fuel tank, sidesteps and drawers to his vehicle so now his kerb weight has increased significantly. Now add tools, luggage, kayak, roof rack, fridge, 2 adults, 2 children, booster seats and bikes and he’s seriously nudging – perhaps exceeding – his GVM.
As they’re hitting the road long-term, their van is fully packed and is pretty close to their GTM of 3000kg. Therefore his current GCM is well in excess to 6200kg … more than what his vehicle specifies and he’s in danger of fines, or worse, an accident!
What’s the solution?
There’s no need to trade in your vehicle for a Monster Truck. GVM and now GCM can now be upgraded through TJM South Australia
You can get a GVM upgrade using a certified compliant Lovells Upgrade kit fitted to most SUV’s. These will give you 300-500kg (depending on your vehicle make and model) of extra vehicle mass so that you can safely add some extra bits and pieces to your packing or rig.
Further to this, the recent backflip by the SA Government means that “GCM revision and towing upgrades can [also] be done on pre-registered vehicles by Second Stage Manufacturers with applicable evidence packages” (Media Release 16 September, 2019 – Lovells Springs). TJM is an authorised installer of Lovells GCM upgrades and compliance testing and certification is provided by an authorised State Engineering Signatory.
In their recent Media Release announcing their win to have the ban on GCM upgrades overturned, Lovells General Manager Mike Davison said: “Without an increase in legal towing capacities, many people towing caravans or trailers have been unknowingly breaking the law and voiding their insurance”. Not a good scenario for thousands of 4WD-ers across the state.
Do I need to upgrade?
The answer to this question will vary greatly depending on your vehicle (make, model and year), how many additions or modifications you’ve made (or are about to have made) and what you’re going to tow.
We recommend you visit your local TJM store and speak to one of our experts who can go through your specific scenario and make a recommendation that’s right for you.
Do you have questions or comments about GVM and GCM? Leave them below and we’ll do our best to answer them.
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