The key to understanding this is to realise that the towball mass doesn ' t magically disappear from the trailer ' s weight when it is connected to the tow vehicle . It is still there ; however , rather than resting on the jockey wheel of the trailer , it now rests on the rear of the tow vehicle . There is no need to add it again .
Therefore , to avoid any confusion , we will look at GVM and GCM separately and assess the remaining cargo capacity with the heaviest-allowed trailer ( 3500kg ) trailer attached to the vehicle , assuming the maximum towball weight is 350kg ( 10 per cent of the trailer ’ s weight ).
The formulas look like this :
• Against GVM , remaining cargo capacity is GVM less the Kerb Weight of the tow vehicle , less the maximum towball weight of 350kg .
• Against GCM , cargo capacity is GCM less the kerb weight of the tow vehicle , less the maximum towing capacity of 3500kg .
You might think these two figures should be the same . Unfortunately , that is seldom the case .
The chart on page 23 shows the calculations for dual-cab utes on the Australian market that boast a maximum 3500kg towing capacity . We have included the discontinued Holden Colorado as it is still a popular tow vehicle . We have also chosen to show the topspec models of each vehicle , so these will be the heaviest of each model in their respective line-up .
The highlighted figures are the lowest of the two remaining payload calculations for each vehicle and the one you must take into consideration .
As you can see , the available payload varies greatly between most vehicles . Most are limited by their remaining capacity against GCM , while just three are limited by their remaining capacity against GVM . We ’ ll come back to this point later .
To put these figures into perspective , you need to look at how much weight you may actually want to put into or onto your tow vehicle to see which of these has the capacity to carry that weight . See table on page 24 .
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