Why a GVM upgrade isn’t all it seems.
A lot of CHECK WEIGHT clients ask us about GVM upgrades and think that can be the answer to the weight problems (tow vehicle and caravan) And sometimes it is.
But not all GVM upgrades are equal – here is why.
Explanation of Acronyms :
GVM Gross Vehicle Mass
GAWR Gross Axle Weight Rating
GAW Actual Gross Axle Weight
For a full list go to
Here’s FIVE Things to check when looking at a GVM upgrade.
GVM upgrade that only gives you your original axle weight limits
We have weighed a lot of tow vehicles who have had GVM upgrades which only give you a total GVM of the GAWR from the manufacturer.
A Landcruiser 200 has a GVM of 3350 kg
A rear axle GAWR of 1950
Front axle GAWR of 1700
So a 3650 GVM upgrade is the total of the GAWR.
However the problem is if you have a caravan and a lot of weight in the back of the Landcruiser. All that weight is on the back axle. And so you may be under your GVM – but over your rear axle weight.
A Landcruiser we weighed which had a 3650 GVM Upgrade
The vehicle (hitched to caravan) weighed 3730
Front axle weighed 1520 GAWR 1700
Rear axle weighed 2210 GAWR 1950
So as weighed (vehicle over GVM by 80 kgs ) but well over GAWR on the rear axle.
(Note : Owner could have reduced load by 80 kg easily which would have also reduced rear GAW by 80 kg.)
GVM upgrade that upgrades your axle weights – but doesn’t give you the weight on the rear axle that you require
Other examples we have seen (using again a Landcruisers as an example) is an upgrade to 3800 kg
Where the upgrade is 1800 kg on the front axle, and 2000 on the rear axle.
The rear axle has been upgraded by only 50 kg – the front by 50 kg – but the GVM by 450 kg. But when you load the majority of the weight is on the rear axle.
It’s impossible to load the vehicle to have 2000 on the rear and 1800 on the front – it’s just not physically possible.
So you think you can load the vehicle to 3800 kg but you actually can’t.
Real vehicle weighed
1560 Front GAW
2010 Rear GAW (on Limit)
Rear at Maximum – but still 230 kg under GVM
This is why we recommend weighing your vehicle hitched to the caravan and fully loaded BEFORE getting a GVM upgrade.
A GVM upgrade that doesn’t actually help because you exceed your GCM
The vehicle a DMAX with a 3450 GVM Upgrade (from 2950)
Front axle GAWR 1450 Actual GAW 1030
Rear axle GAWR 2000 Actual GAW 2070
Actual GVM 3100 kg but rear axle over GAWR
Note – and adjustment in loading resulted in rear axle being under.
Also you can see that loading the rear axle to the limit – decreasing the load on the front axle – in this case its potentially dangerous as a low front axle weight will affect your steering and front wheel braking – especially in wet conditions.
Now the GCM is still 5950 for this DMAX so the more you load the vehicle – the lighter the caravan that you can tow. So in this case the maximum GTM of the caravan can be 2850 (tow ball weight included in GVM when vehicle weighed).
So the upgraded vehicle means you can’t tow a 3.5 t caravan fully loaded !
In your owner’s manual you will see GAWR – the maximum – but unfortunately there are NO front axle minimums !
It would be nice to see (I won’t hold my breath) because its the low front axle weight which gives you steering and braking issues.
Can the vehicle actually cope with the extra weight
A GVM upgrade is so you can carry extra weight, so can the vehicle actually cope with the extra weight?
The performance, reliability and fuel economy will be compromised if your pulling too much weight. The Vehicle has been designed to cope with the GVM set by the manufacturer – and of course there is a tolerance – so when upgrading the maximum weight of the vehicle be aware that this could impact on fuel economy, stress on the drive train and potentially the reliability and long term life of the vehicle.
# 5 Who is covering the warranty if something goes wrong ?
If you get a GVM upgrade post registration – but the vehicle is under warranty – will the original manufacturers warranty still cover a failure ? We aren’t talking the suspension bits. Maybe your gearbox packs it in – The vehicle manufacture / dealer says you are not covered as you have modified the vehicle and you are carrying / towing to much weight.
The Engineer who did the upgrade says – gear box – nothing to do with us.
Could be a problem. Who is going to pay ?
And remember to tell your Insurance Company that you have modified the vehicle – as the modification could void your Insurance if it’s not noted on the policy.
(I am not saying this will happen – its been raised on various forums as a possible problem !)
The above are not necessarily the engineers and companies offering GVM Upgrades fault.
If you take your vehicle in empty and not hitched to a caravan – then the engineer is estimating your needs.
That’s why some engineers love the reports we produce showing the vehicle fully loaded – hitched to the caravan – with wheel and axle weights.
Get a few quotes and get a GVM upgrade from and engineer who looks at your needs and just doesn’t give you an “off the shelf” one size fits all upgrade !