GVM upgrades can be extremely useful, and are really the only way to make an overweight 4WD comply. However, there are some downsides to them, and if you intend on running at maximum GVM and towing the maximum towing capacity, you might be in for a rude shock.
If you are new to learning about weights, we have a super easy to understand post that explains everything together, in detail here – Towing Capacity.
What is a GVM upgrade?
In order to answer this well, lets start right at the beginning. Every single vehicle that rolls off the assembly line is given a GVM, or a Gross Vehicle Mass. This is the maximum amount that it is allowed to weigh at any given time, and is the total weight being applied to your 4 tyres.
This means its the weight of the vehicle, anyone in the vehicle, any accessories you install, gear you take and the forgotten piece of the puzzle; any weight that your trailer passes onto the vehicle in the form of tow ball weight.
On top of this, you have axle capacities, which are the maximum weight that you can apply to the front, and the rear axles of your 4WD. This is done so your vehicle stays balanced; you can’t expect to add the entire payload of the vehicle behind the rear wheels, as it will exceed the rear axle capacity (and often well before you hit GVM).
A GVM upgrade is the signing off of a 4WD to allow it to have a higher GVM. This can be done to an extent without any physical modifications, but in most cases it involves adding a new set of suspension. This is generally springs, shock absorbers and then a modification plate that is stuck to the vehicle to state its new load carrying capacity.
In some cases, a GVM upgrade will also upgrade the axle capacities, which means you can then legally carry additional weight on each axle (and is necessary to get to the much higher GVM).
When do you need a GVM upgrade?
If you take your vehicle to a weighbridge and find that it weighs more than the GVM, you either need to shed weight, or get a GVM upgrade. It’s important at this stage to think longer term though; if you are way over weight sometimes even the biggest GVM upgrade isn’t going to solve your problem.
It’s also the time to think about what you might tow later on, as I’ve seen plenty of people get a GVM upgrade, and then a new caravan and have to sell their vehicle as its not suitable.
Does a GVM upgrade reduce your towing capacity?
Yes, it does in some cases, and here’s why. Along with your GVM, you also have a GCM (Gross Combination Mass), which is the total weight of your vehicle and trailer moving down the road.
When you add your GVM and maximum towing capacity, ideally you should be at, or under the maximum GCM. Unfortunately this is often not the case, which is where some of the marketing spiel catches people out, and it really frustrates me to see people getting burnt.
To make it even worse if you increase the GVM from the factory without touching the GCM, it hits even harder.
To make it easier to understand, lets do a practical example.
Our 2016 Dmax has the below
- Factory GVM – 2950kg
- Factory maximum towing capacity – 3500kg
- Factory GCM – 5950kg.
Already, you should see a problem. The GVM and towing capacity exceed the maximum GCM.
2950kg plus 3500kg is 6450kg, which is 500kg over weight. In reality then, at full GVM, we can only tow 3000kg. What do you think happens if I get a GVM upgrade (like we did), which takes the GVM to 3220kg?
5950kg minus the new GVM of 3220kg is a maximum towing capacity of 2730kg (when the vehicle is fully loaded), which is a big drop. If we had gone for a Pedders GVM upgrade of 3450kg, it would reduce the maximum towing capacity down to just 2500kg.
In short, a GVM upgrade will reduce your towing capacity at full weight, and hopefully the above example makes this clear. Please know that if your actual vehicle weight is lower, your towing capacity remains higher.
For example, if you had a 3450kg GVM upgrade, and your vehicle only came in at 3200kg, your towing capacity would be 5950kg minus 3200, making it 2750kg. If you lost another 200kg from the vehicle, your towing capacity would go up to 2950kg. It’s entirely relevant to actual weights.
Can you get GVM and GCM upgrades?
The only way around this then, is to get a GVM and GCM upgrade. If we could take our GCM to 7000kg with a Lovells GCM upgrade then you can still tow 3500kg.
However, you can’t get GCM upgrades in some states, especially if the vehicle is already registered.
Don’t push the limits
I’ll probably upset a few people here, but I’d rather be honest and blunt than mislead you. If you need a significant GVM and GCM upgrade, you have the wrong vehicle for the job.
Yes, you can tow a 3300kg with a Dmax that weighs 3400kg with the right kit, but everything on the vehicle is going to be working its guts out, and is far more likely to break.
Every vehicle has some leeway for additional stress, but some of these kits explain why so many people are snapping differentials, or bending Ute chassis.
If you want to tow something heavy, a normal 4WD at the end of its limits with a GVM/GCM upgrade is not the right vehicle for the job. There are some exceptions, like a 200 Series or Y62 Patrol that will take the extra punishment, but you’ll still wear them out quicker.
Do you have a GVM upgrade? Did you know it can hurt your towing capacity?