GVM, GCM, Tare, ATM, TBD, Kerb Weight, the list goes on. There is so many different abbreviations in the towing community that it’s hard to keep track, so we’ve explained them as simply as possible to help everybody get on the same page.
Tare Mass or Weight
This is the weight of an empty standard vehicle. A vehicle weighed for Tare only has 10 litres of fuel in the tank (10 litres was chosen as an industry standard). This is the base weight of your car with nothing in it.
Kerb Mass or Weight
The same as tare, but with a full tank of fuel and without any accessories fitted (bull bars, tow bars, roof racks etc). Think of it as your standard vehicle parked at the kerb and ready for you to get in and drive away. We use kerb mass to calculate other variables.
GVM (Gross Vehicle Mass)
This is the maximum your vehicle can weigh when fully loaded as specified by the manufacturer. You will usually find this GVM figure on the vehicle’s weight placard (generally found in the driver’s door opening) or in the owner’s manual. You can upgrade the GVM on most vehicles by adding upgraded suspension, just like we do with the RAM 2500. We add new heavy duty coils, shocks and optional 40mm lift and rear airbag suspension to push the stock GVM of 4.5 tonnes to 5.3 tonnes. This upgrade does not increase your gross combined mass (GCM), which leads us to our next towing term.
Gross Combined Mass (GCM)
This is the maximum weight allowed for your vehicle and trailer combined. Simply explained: your vehicle can only tow whatever your stated GCM – GVM is. So you take your GCM (for example lets use 5000kg), subtract your vehicles GVM (lets use 3000kg) and you’re left with your maximum towing capacity, 2000kg.
This is simply the maximum load your vehicle can carry as specified by the manufacturer. Just deduct your vehicle’s Kerb Mass from its Gross Vehicle Mass (GVM) and what’s left is what your vehicle can carry. This includes passengers. If you vehicles payload is only 1 tonne, then 5 hefty guys will easy fill half of this and you will only have approx. 500kg left to load into the vehicle.
Tow Bar Download (TBD)
The amount of weight on your tow bar is crucial to safe and efficient towing and needs to be mentioned here. Any quality tow bar will have a placard or similar showing the maximum tow bar capacity (kg) and maximum tow bar download (kg). Make sure the tow bar you choose is designed specifically to suit your vehicle and your towing capacity requirements. To add TBD to your GVM, subtract approximately 10% of your gross trailer mass. For example if you have a GVM of 3000kg and your GTM (see below) is 2500kg, you instantly need to consider your TBD is applying approx 250kg worth of weight that impacts your GVM.
Gross Trailer Mass (GTM)
GTM is the weight of the fully loaded trailer imposed on the trailer’s axle when it is coupled to the tow vehicle. Easily put it’s how much your trailer weighs when loaded.
Aggregate Trailer Mass (ATM) or Weight (ATW)
This is the Gross Trailer Mass (GTM) plus the Tow Bar Download (see above). In other words, the ATM is the maximum towing weight of the trailer/caravan as specified by the manufacturer.