Anything is possible… provided you’re prepared to pay for it. It would certainly be technically possible to convert a Sprinter van to dual rear wheels, but you’d need to source a rear axle that both mounted the dual wheels as well as being compatible with the van’s existing suspension and braking systems. Perhaps there’s a version of the Sprinter (perhaps sold overseas) that would be a donor for such a thing, but you might need to look further afield to find the bits and pieces necessary for the conversion.

But even if you can physically make it all work, there’d be a significant cost in getting the modified vehicle re-engineered (and tested) to ensure that it was still safe to drive on public roads. Until then, the van would not legally be roadworthy. You might also find that your insurance company would take a fairly conservative view of such a conversion, too.

I think you’d need to budget several thousand dollars for such a project. Assuming the conversion was to increase the van’s payload, you might find that simply buying a different vehicle with the payload you require might be the simpler, cheaper route. Also, a Sprinter converted to dual wheels might be more difficult to unload when it’s time to trade up to a new vehicle.

This is an increasingly common problem for people who carry big loads and especially for those who tow heavy trailers. In some cases, as you've discovered, it's very easy to get perilously close to the GVM limit by loading up the vehicle with whatever you're carrying. And that's the catch; the vehicle's GVM includes everything on board including passengers, fuel and whatever accessories you've added to the car, not to mention the actual payload.

Earlier this year, Queensland changed its rules regarding GVM upgrades, but you would need to speak to a specialist workshop that deals with this type of work and is familiar with the QLD regulations which may vary from other states and territories. Companies such as Pedders are qualified to carry-out GVM upgrades on some vehicles and have the engineering experience to offer a package that is certified before it's fitted to your vehicle. Whether the Sprinter's body construction has any bearing on the availability of such a kit is another thing you'd need to check with a specialist.

The problem with exceeding your car's GVM is that it makes its potentially unsafe to drive for both you and other road users. You'll also find yourself in line for a fine and your insurance company is likely to disown you in the case of a crash in an over-loaded vehicle.

Normally it should be about halfway on the scale, but it could go higher than that and not be a problem as long as it doesn’t get close to the top mark.