On two axles, the Max Gross Weight is 18 tonnes.
On three axles, the M.G.W. is 26 tonnes.
On four axles, the M.G.W. is 34 tonnes.
Many wagons with whatever number of axles can be plated for a lower M.G.W. depending on all sorts of different reasons. The owner might need the volume to haul light bulky loads (for eg), so buy a downplated 18 tonner which could have a body larger than is possible on a 10 tonner chassis. I could also, in this example, be talking out of my rear 
, but you get the idea I hope 
.