Hi Geoff,
The maximum ball weight for Australian D3's and D4 models is 350kg, not 150 kg. Mind you that is reliant on you not loading the D4 up to its max carrying weight though just like it would be with any vehicle.
That is unless LR have just decided to make sure no grey nomad will ever buy a new Disco ever again.
Still having said that if I was going to buy a new D4 I would now be asking for written clarification on the max ball weight and what is stated on their website to be on the safe side re insurance etc.
cheers,
Terry

