A Gross Combination Mass (GCM, also maximum authorised mass, MAM) is the maximum allowable total mass of a fully loaded motor vehicle together with all of its trailers. It is the sum of the maximum Gross Vehicle Mass (GVM) and the Gross Trailer Masses of all of the trailers is allowed to be.
The GCM is a function of the torque output of the engine, the capacity and ratios of the transmission, the capacity of the driving axles and tyres, and the ability of the chassis to withstand that powertrain torque.