Navarra D22-2009 twin tyre racks

G'day Jackson
Can't help with the supply aspect.
The associated weight of the carrier system, whatever it may be, will be another wheel of weight at least, so in reality it will be at least three wheels added to the very back end of the chassis. Possibly even further away than the chassis.
All that weight well behind the rear axle and combined with tow weight if ever/also towing sometimes, would place a high degree of bend stress on the chassis in the region behind the cab. ie, before the upward curvature and rear spring hanger.

Many Navara's have bends in the chassis because of loading behind the rear axle. While other vehicles are also subject to the same, there seems to be more N's than others with bent chassis, whatever the cause.
May be Ok if used on road ie, smooth roads, but where sudden high forces caused by off road use, as a result of the mass of load and "rear gear", especially if the loading on the rear axle bottoms the suspension, I would be careful with the fitment.
A raised and compliant, non bottoming suspension may be the way.

Just being cautious.

Thanks for the insight

Pete

Don't ignore the advice given by Ross, it could easily save you from a lot of inconvenient and expensive chassis repairs.

The section of the chassis, plus the tub or tray, that extends back behind the rear axle is a lever. If you keep adding things to it, it will eventually force the rear end down and and lift the front wheels off the ground as the chassis pivots on the axle. If you actually did try doing that, the chassis would bend while you watched it somewhere between the front hangers for the rear spring back to the area above the axle.

In practice nobody puts that much weight onto their cars but the vast majority seem to forget that the situation changes dramatically when whatever they have behind the axle is in motion.

Your wheels would weigh at least 30 kgs each. The mounting bracket would most likely be over 20 making a very conservative total of 80 kg. Your tow ball would be around 1200 mm behind the axle.The tub or tray could go back a bit further. The wheels would be off the end of that making them at least about 1400 mm back. That is a long lever. As your rear wheels fall into a depression in the road, the chassis will fall suddenly. The forces generated by those falling wheels will increase by the square of the distance they are behind the axle. That works out to a force of 157 kgs if my maths are correct. On top of that you can add to it the forces generated by whatever else you have behind the axle.

A split second later your car wheels might come back up out of the depression quickly. The falling material in the back will have to be caught by the end of the chassis and heaved up instantly. Imagine what this is doing to the end of the chassis.

The same thing is happening when your front wheels rise and fall. The rear end of your chassis is going up and down in the opposite direction. The chassis is heaving the weight up and catching it when it comes down.

This makes it very difficult to load these type of cab/chassis utes without over-stressing the chassis. The handbook for mine for example (not a Navara) says a WDH must be used for any tow ball weight exceeding 90 kg. A WDH is not a spring but a lever that picks the rear of the chassis up and transfers weight forward to the front wheels. If I was to mount two spare wheels on the back of my car, I would have more than 90 kg hanging out past the tow ball but I could not use a WDH to move some of that weight forward because I am not towing anything. Herein lies the big problem. Owners can carefully load their utes making sure the car is not over GVM, or the axle load limit, but have so much out the back that the chassis is way outside the factory design limits. This is why countless utes of all makes have bent or cracked their chassis.

The problem can not be fixed with a heavier suspension. Aftermarket springs may make the car sit up a little higher and look better but the weight is still out the back and still generating the same forces as the chassis moves up and down.

Just a question... why two spare tyres?

Most who think they need two spares never end up using them, a good tyre monitoring system and plug kit is all we use.

You could try this mob.....

http://www.bigo4x4.com.au/