Curb Weight

Going into the Australian Bush requires the intrepid traveller to carry substantial supplies of water and fuel, as well as the normal requirements for living off-grid for extended periods. This is quite different to the norm in international overlanding where fuel and water is usually available in small towns, and is due to the very (incredibly) low population density of the Australian Bush. The population density of the Australia’s Northern Territory is 0.16 people/km2, about 1/100th of the density of Argentina with 17 people/km2, or 1/25th of Botswana with 4 people/km2, for example. So the purpose of my lists is to estimate the weight required to travel with some comfort across long desolate desert tracks, before the required fuel and water supplies are added.

Load Calculation

Whilst my lists remain incomplete they are a useful tool to establish the the total equipment and supplies budget, and then contemplate the best method to carry everything. My current calculation shows that the normal total mass estimate is around of 575kg, including fuel and water. A rough breakdown of the categories is below.

  • Recovery Equipment – 50kg
  • Vehicle Spares / Consumables – 20kg
  • Tools – 30kg
  • Camping Equipment / Tents / Tarps – 90kg
  • Battery & Electrical – 50kg
  • Refrigerator / Slide – 45kg
  • Cooking Utensils – 20kg
  • Computers / IT / Camera – 20kg
  • Clothes / Blankets / Linen – 30kg
  • Food – 30kg
  • Unclassified / Toys – 20kg

Adding to the items above, is necessary to carry water sufficient for 20 days. And fuel to bridge the longer distances between services.

  • Water 100l – 100kg
  • Fuel (incl. Jerry Can) 40l – 50kg

The weight budget must also allow for carrying 60l to 100l of exceptional fuel load to traverse long tracks in the desert where it would be foolish to commence the journey with only 100l (including the vehicle tank of 60l). For some extreme tracks, the recommendation is to start with a minimum total of 200l, allowing for reserves and safety margin.

Now that might look like I’ve budgeted to carry a lot of stuff, but the idea is not to load up to 100% capacity before departure. But rather the calculation is intended to to allow room for growth as over time, as stuff tends to accumulate, and trophies and memorabilia will take up their share of space too. Nobody likes to climb into a vehicle and have their stuff fall out on the road because everything is packed to the roof.

So, I’m going to estimate that a total payload budget of 600kg will be sufficient. How can that payload be effectively carried across sand and rock over thousands of kilometers?

Carrying the Payload

As a starting point, the Jeep Wrangler JL Rubicon 2 door is the chosen vehicle for going bush.

Jeep Wrangler JL Rubicon 2 Door – 2022 – Marketing Image

From the 2020 Wrangler Specification, the Rubicon can carry a maximum payload of 1322lbs, or 600kg, in the 4 door version. The 2 door version has similar mechanical specifications but weighs about 100kg less, but I will assume that it can’t carry a greater payload than the larger 4 door version. Maximum braked towing capacity for the 2 door version is 1497kg. Let’s have a look at some of the options for carrying 600kg with a 2 door Rubicon.

In the above images I’ve considered some alternative solutions for carrying 600kg payload (in green), and the maximum usable axle load (in red) for the vehicle. My alternatives include:

  1. Bare Vehicle – everything inside the vehicle
  2. Roof Rack – 450kg in vehicle, 150kg on roof (and outside)
  3. Roof Top Tent – 500kg in vehicle, 100kg of RTT (and outside)
  4. Box Trailer – 200kg in vehicle, 400kg in trailer
  5. Pod Trailer – 200kg in vehicle, 400kg in trailer
  6. Teardrop Camper – 200kg in vehicle, 400kg in camper

Bare Vehicle

The Wrangler 2 door is a very small vehicle and, although it is probably the most capable 4WD available “off the showroom floor”, loading it up to the maximum payload will make a very uncomfortable origami that would need to be unfolded at each camp and then intricately repacked each morning. Additionally, as the maximum rear axle payload is about 1000lbs, or 450kg, the available payload would be limited to less than the maximum vehicle payload, as there would be no way to share the weight to the front axle.

In my opinion only way to carry 600kg on a Rubicon is to distribute the weight onto both axles by using a Roof Rack.

Roof Rack

By adding a roof rack, and possibly also side racks for fuel and a rear rack for tools and fuel, it is possible to distribute the weight onto both axles, and also increase the load volume of the Rubicon sufficiently to reasonably store the maximum vehicle payload.

The cost for roof rack system consists of a base rack of around A$1,000, guard rails at around A$500, and then vehicle specific mounting kits from around A$400. Accessories to mount shovels, high lift jacks, jerry cans, or gas bottles can be added for around A$200 per item.

Adding a roof rack will increase the loading on the front axle and especially the rear axle up to the maximum design rating of 3100lbs, or 1400kg, and will increase the tire load affecting both sand driving ability and the tire wear characteristics. Axles, wheels, and tires will be running at maximum load constantly. Adding a lift-kit to balance out the spring compression will not resolve this loading issue, and it is likely that the vehicle may end up being over-weight from a legal (insurance) perspective.

Using a roof rack will also significantly impact the dynamics of the vehicle. Adding up to 100kg onto the roof and 50kg to the outside of the vehicle will increase the overall pitch and roll as the track pushes the vehicle around. It will be very uncomfortable, and may actually become unsafe as the maximum approach and departure angles are reached.

On road, which will be the majority of the kilometres travelled, fuel economy can suffer by 10% and up to 25% according to some reports. Where tens of thousands of kilometres are at stake, and fuel is both in limited supply and expensive, it is best not to use a roof rack if there are better alternatives.

Roof Top Tent

The roof top tent suffers from the same dynamics and fuel economy issues as the roof rack, and it is also of very limited application being purely a place to sleep. If a roof top tent is fitted then the top of the vehicle can no longer be used for storing equipment.

A roof top tent costs around A$,5000, but considerably more can be spent if desired.

With the issues associated with roof top tents being the same as with roof racks and offering no other advantages, it is better to seek alternatives.

Box Trailer

Many people have realised the benefits of an additional load carrying axle when travelling around Australia. The typical steel box trailer in the standard 6’x4′ or 7’x5′ single axle configurations lives in most suburban back yards, and has been making the journey to the summer camping holiday since forever. It has become more common recently to add off-road suspension and hitch components to make the box trailer capable of serious expeditions.

The typical suburban box trailer costs around A$1,500, but the vehicle must have a trailer hitch which can cost up to A$2,000 to install, depending on the vehicle. An off-road trailer with uprated suspension and chassis typically starts around A$5,000, but specialist camper trailers can be substantially more. Some fully fitted off-road box trailers cost upwards of A$60,000.

The design and registration of box trailers typically focusses on a gross vehicle mass (GVM) of 750kg and their Tare is typically 250kg, in the best case, leaving a payload capability of 500kg. If our total load can be distributed between vehicle and trailer then we can load the trailer with 400kg, leaving a margin of 20% remaining, and reduce the vehicle load to 200kg.

The load in a trailer is carried with a low centre of mass, so that the dynamics of the tow vehicle are not affected, and having the additional loaded trailer axle reduces the wear on the vehicle axles, wheels and tires.

However, towing a box trailer does not come for free. There is an increase in fuel consumption to be expected from towing. Depending on the size of the load carried and the amount of wind drag created by the trailer, the increase in fuel consumption may be up to 10%. This is significant, but it is much less than if a similar load were on a roof rack. And, as we now have a greater free load capacity it is possible to carry up to 100l of extra fuel as needed.

An important advantage to using a trailer is that it can be disconnected from the vehicle and left behind at a camp site, or trail head, when its contents are not needed. Through this method most of the payload associated with living does not need to accompany the vehicle on a difficult 4WD trail. This minimises the chances of breakage or damage to the payload.

The box trailer has several disadvantages. Firstly, the load is carried open and unsecured, and secondly, the payload is subject to dust and sand from both the vehicle rear wheels and the environment generally. Whilst Australia is generally safe, for piece of mind, it is best to keep valuables and equipment hidden out of sight when the trailer is left behind. So box trailer loads are usually covered by a tarpaulin or load cover. This adds to the soft security of the load, and helps to prevent dust and sand ingress, but it is time consuming to wrap and tie down the load each morning.

There are many advantages to using a simple box trailer to carry the payload, but it would be more ideal if the box trailer load could be covered by a solid lockable lid to secure the load and mitigate dust and dirt ingress.

Pod Trailer

Recently advances in plastics technology have enabled the creation of large roto-molded polyethylene structures, and companies have started to produce off-road “pod” trailers using polyethylene tubs and lids jointed like a clam shell and sealed with a gasket to produce an effective dust seal.

Typically these pod trailers incorporate all of the advantages of the box trailer, adding in the tare weight saving of a dust resistant plastic tub and sealed lid, and the aerodynamic efficiency of a smooth load top.

Many pod trailers can carry a payload of 750kg to 810kg, with their GVM being 1250kg with trailer brakes. An extreme off-road pod trailer can cost from A$13,000, and customisation and options can be added to increase the suitability for long distance expeditions.

With an appropriate off-road independent suspension, hitch, and trailer brakes, a pod trailer can follow behind a vehicle on all but the most difficult 4WD tracks. And where necessary the secure lockable pod can be left behind at a camp site or trail head.

Teardrop Camper

Moving up from the box trailer or pod trailer solution, it is possible to consider a teardrop or square drop camper. The key advantage of the camper is that the question of sleeping arrangements is answered by a permanently made bed. At the end of a day, or when weather is bad there is a lot to be said for a ready-made bed.

A teardrop camper is usually a significant Tare approaching 900kg, and they can usually carry at least 400kg and up to 800kg in payload. They can easily accommodate the 400kg we need to carry. However the camper GVM will certainly be approaching 1,900kg when fully loaded. This is about 1 Tonne more than a box or pod trailer.

Teardrop campers range in price from A$50,000 and up to around A$100,000, making them potentially more expensive than the tow vehicle.

Besides the large GVM of the teardrop camper, there is a cost to transport the volume for a bed and “sleeping space” around the country. The cost comes in increased the form of increased drag and increased fuel consumption from the larger box, and in reduced space to store camping equipment, unless the potentially dirty equipment is transported on top of the clean made bed.

Conclusion and Decision

Following on from the discussion above, I have decided to go with the pod trailer solution. Although using a trailer will close off some of the more extreme trails and options, such as parts of the CSR, the flexibility to leave the pod and equipment safely behind at the campsite, and have the small tow vehicle remain relatively unmodified (no heavy duty springs, or body lifts, etc), together with the other points discussed above, make the pod trailer the best value for money.

The pod trailer has some further advantages that I’ll discuss in a post on Sleeping Arrangements, and also further in Redundant System Design.

2 thoughts on “Curb Weight

  1. Pingback: Sleeping Arrangements | Gone Bush

  2. Pingback: Test Camping | Gone Bush

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