4WD MODIFICATIONS - GENERAL MODS
These calculation tables are designed to make it easy to assess the effects of payload and towball weight when towing. Caravan and trailer weight distribution can also be calculated.
There are three main reasons for ensuring your solo vehicle or vehicle and trailer complies with the makers’ axle weight limits: safety, legal and insurance issues.
The safety implications of operating overloaded vehicles are obvious: more likelihood of braking, handling and tyre failure issues.
If you’re weighed at a roadside inspection station and found to be overloaded, you’re in trouble. State and territory authorities have zero tolerance for any axle that’s overloaded, even if the vehicle or vehicle and trailer are within GVM and GCM limits: one overloaded axle is sufficient case for a hefty fine and a vehicle ‘grounding’.
In the case of vehicles towing heavy caravans that overloaded axle is always the rear drive axle.
Insurance companies have become much more vigilant about vehicle weights and may weigh a damaged towing vehicle and trailer before agreeing to process a claim. Many claims have been rejected on the grounds of illegal loading.
If you’re still reading that means you’re interested in towing safely and legally.
Before you progress to our distribution calculation tables can we suggest you read the following topics that are in our Towing section: Australia’s towing laws need to change; ADRs and VSBs not enough to guarantee safe trailers and caravans; Tow Ball weight and trailer stability; Don’t believe 4WD makers’ towing ratings; Electronic stability control; Towing correctly and Safe and legal towing.
Yes, it’s a big read, but this is a life or death topic!
Calculating vehicle and trailer weight distribution
Until now, it’s been very difficult to ensure your vehicle and or trailer are legal, but our OTA calculation program allows quick guidance in this critical area.
The starting point is with actual weighbridge weights for your vehicle and trailer, and the unladen towball weight. The vehicle and the trailer need to be separated and weighed, with the trailer axles only – not the jockey wheel – on the weighbridge. Towball weight its best measured with a scale – around $80 at automotive outlets.
It’s best to start with a completely empty setup, but with a full fuel tank.
Then you need to find the maximum axle weights permitted by the vehicle maker(s) and/or tyre load ratings, and the maximum towball load allowed.
Next is to make sure you have correct dimensions for front and rear overhangs, and the wheelbase. Ditto for the trailer.
Using the ‘hamburger’ menu, you then enter the relevant weights and dimensions.
‘Playtime’ involves putting the weights of your vehicle and trailer payloads into the locations set out in the tables. When you move a weight to another location, the effect on axle weights is calculated automatically.
Our default vehicle is a 200 Series LandCruiser GXL, but you simply replace the sample values with those for your vehicle. If it’s a short-cab ute, not a wagon, the ‘back seat’ location is the forward end of the cargo tray.
Likewise, the trailer shown is a single-axle van, but, if you have a multi-axle van, put the axle weights for it into the table. Likewise if it’s a camper trailer: just enter the dimensions and weights.
We’ve split the payload areas into ‘zones’, but if you don’t have that many loading areas, just ignore the ones that don’t apply.
When measuring the trailer dimensions from the towball receiver to the load zone, measure to the mid-point of that zone. For example, if the loading area is a storage box on the chassis, measure from the towball receiver to the middle of the box.
In the case of ‘people payload’, measure from the front of the vehicle to the hip points of the front and rear seat rows and estimate the weight of passengers in those rows.
If the load area in a particular zone is large enough to embrace what might be two zones, just pick the mid-point dimension between the two zones.
When you’ve entered all the relevant weight and dimension data the axle and towball weight boxes automatically update with calculated totals. If the boxed figures remain ‘green’ that’s good, but if a box turns red the weight in that box exceeds the legal or manufacturer’s rating.
The calculator can’t include the weight transfer effect of using weight distribution bars, because their size and degree of tension are variables. However, the calculator shows coupled-up rear axle weight, allowing you to see if you need to transfer some of it.
Note that weight distribution bars don’t ‘remove’ ball weight, but transfer some of it to the tow vehicle’s front axle and the trailer axle(s). The calculator shows how much reserve weight capacity you have at the front axle and at the trailer axle(s).
Important point: if you wish to retain the figures you’ve input you’ll need to take a screen shot or print the page that’s on screen. Once you’ve clicked off the OTA webpage your input dimensions and weights will revert to the default ones.
Also, please read the following disclaimer:
Outback Travel Australia offers this calculator as a guide only and does not guarantee, and accepts no legal liability, for the accuracy, reliability, currency or completeness of this material.
You should seek appropriate, independent professional advice before making any decisions based on material found on the www.outbacktravelaustralia.com.au website.