GCM- GROSS COMBINED MASS

GCM applies to those of us who tow caravans, trailers, boats etc. GVM is the maximum your fully laden vehicle and trailer can weigh as a whole.

eg: Your vehicle weighs 3000kg loaded + Caravan 3500kg = 6500kg, the GCM of your vehicle is 6500kg, this means you are within your maximum limits.

The GCM of your vehicle is specified by the Manufacturer and does not change when having a GVM Upgrade.

Areas of concern eg: Your vehicle weighs more than the specified GVM and you have a GVM upgrade installed, the GVM Upgrade allows your vehicle to weigh 3500kg, your GCM is 6500kg (as specified by the Manufacturer and doesn't change with a GVM Upgrade) you add your caravan- 3500kg + 3500kg = 7000kg

You have exceeded your GCM and your vehicle is illegal.

If you have a GVM Upgrade installed and max it out at the new numbers, hitch up a caravan, you will most likely be over your GCM, so if you are considering a GVM Upgrade and tow any vehicle, you need to keep a close eye on your GCM.