GVM, BTC, GCM and Axle Loads.
Why these are so important.
You’ve more then likely heard these terms before but what do they actually mean and how do they affect your vehicle?
GVM
GVM stands for Gross Vehicle Mass, this is what your vehicle’s maximum weight is allowed to be loaded to and is also heavily affected by axle load capacity. On the standard 79 Series Landcruiser your complete vehicle can only weigh a maximum of 3300kgs and if you use our calculator below you will see how easy it is to load your vehicle up to maximum GVM quickly.
Now when it comes to purchasing a GVM upgrade not all kits are the same, there are 4 key areas a GVM upgrade needs to address.
- SUSPENSION: Can the springs carry the extra load and are they rated correctly for the application? The same for the shocks not only can they control the extra load, but is the dampening up to the job? When all that extra weight is being thrown from side to side or up and down is your suspension up to the task?
- BRAKING: Are the factory brakes up to the job with the extra weight? Can they stop your vehicle in the required distance with all the extra weight?
- DRIVELINE: Will the vehicle’s driveline be capable and reliable with the extra load? What’s the point of being able to carry all that weight but your driveline isn’t up to the job such as the clutch, gearbox, engine, differential.
- AXLE LOADS: Can the stated axle loads of your GVM allow practical loading of your vehicle? GVM doesn’t actually mean anything if you have small axle load capacity as this is the limiting factor of what can be loaded in your vehicle
So when it comes to choosing a GVM upgrade for your vehicle does it tick those four boxes? If not you have to ask yourself is it a true and usable GVM upgrade or are you just wasting your money?
BTC
BTC stands for brake tow capacity, now this one is heavily affected by the GCM on your vehicle and determines how much the vehicle can actually tow legally.
To give you a example of this if your vehicle has a GVM of 4000kg and a BTC of 3500kg but the GCM of the vehicle is only stated at 6800 this means when you load your vehicle to 4000Kg you can now only tow around 2800Kgs.
Without a GCM increase the total amount you can tow is reduced by the amount exceeds the OEM GVM.
Axle Loads
Why are axle loads important?
Stated axle loads are very important because these determine on where the weight can actually be loaded on a vehicle.
As an exaggerated example if you vehicle has a GVM of 4000kg and the rear axle load is only stated at 2300kgs this means you would only be able to load the rear of your vehicle up to 2300kgs and the rest of the weight will have to go on your front axles of 1700kg.
Now this is near impossible and impractical to do unless you have a tray mounted to your bonnet, so you can see how your axle loads play a big roll with your GVM.
The higher you go with the GVM you need the correct rear axle load capacity to be able to practically load your vehicle. So then how do you get axle loads and where do they come from?
True Axle loads are stated from the 1st stage manufacturer of the differential housing for example Toyota’s rating on their rear differential housing is 2300kg and Jmacx’s rating on their housings are stated at 2700kg’s-3000kg’s these two manufactures have stated their axle load ratings and should not be re-rated by anyone else.
These products have been manufactured to achieve a rating and have safety margins built in to them it is not appropriate for other companies to simply re-rate them, safety margins are there for a reason for example extreme condition such as corrugation, harsh terrain and long term fatigue.
Some OEM manufactures axle rating have a small ability to rerate but anymore than 10% would reduce your safety margin. Noting that some vehicle’s axles have no ability to be rerated.
GCM
GCM stands for Gross Combined Mass. This effects what your vehicle can be loaded to and tow at the same time and now this can be heavily effected by what GVM your vehicle has.
An easy way to explain this one is if you add the GVM of 3300kg to the BTC of 3500kg this equals a stated GCM of 6800kg meaning your vehicle can weigh 3300kg and tow 3500kg at the same time.
Now for a example of when it changes, if you have a vehicle with a GVM upgrade of 3900kg and you add it to the BTC of 3500kgs but the stated GCM is only 6800 it wont equal up and thus you need to control how your vehicle can be loaded with this combination and you could still only load your vehicle to a maximum of 3300kg when towing 3500kg.
Note that not all companies offer a GCM increase but only offer GVM increase maintain OEM GCM.
Use the GVM weight calculator below to find out what your vehicle weighs.
Disclaimer: all weights used in the calculator are an estimate only. For a more accurate weight of your vehicle and to find out your individual axle loads please visit your local weigh station to get a reading.
GVM Upgrades
Designed for load carrying touring/work and service vehicles when you need both stability & safety.
