If you take the family, food, clothes, drinks, camping gear, surf boards, the dog and kids’ bikes with you on holidays (and who doesn’t) the total weight of all this stuff is one thing.
But, it’s where you carry these things in the car, on the car or the trailer, or even in the camper or caravan that can make a big difference.
These items don’t just add up to make a new weight. Where they’re carried affects ball loads and axle loads – and of course safe handling of the total rig.
The impact on ball loads and axle loads can be seen as quite simply levers over a pivot (or fulcrum).
Levers can be considered as the body of the car, trailer or caravan / camper.
While the pivots are, in very basic terms, the axles of the car, trailer or caravan / camper.
Again, in simple terms, the wheelbase of the car has a role to play in all this, as does the overhang of the tow hitch (ball) behind the car’s rear axle if you’re towing.
Free Load Calculators for You to Use
When I had my camper trailer weighed, I went in full of confidence in the knowing that I had had my Mazda BT50 upgraded with a 3.5t Gross Vehicle Mass (GVM) and a 7t Gross Combination Mass (GCM).
But, I was to be surprised by the load of the trailer on the ball – and the resultant load on the rear axle of the car.
Like many travellers in this situation, my initial thoughts were what can I leave at home and where should I move the stuff I’m carrying to make the required difference to the loads.
Normally, this would mean having a ‘stab in the dark’ and hoping I’d got it right and I was good to go on my next trip. Then again, I could always go back to the scales and see what difference my load shedding and movements had made.
This is when I got to thinking that there must be a quick way to test these load shedding and relocation strategies – at the desktop. This way, people like you can do a whole lot of what-if scenarios at work, or on the train to see how much of a difference these things may make.
The other use for the these desktop calculators is where people contemplate adding say six bicycles on the caravan drawbar (A-frame) or on the rear of the van / camper. As I say above, the multiplier of these loads with the lever affect can be much more that the load itself.
Now, after nearly 12 months in the planning, I’m happy to share with you some free calculators that I hope you find helpful and informative.
These calculators are:
- Load Table 1 – Ball to Car Rear Axle Load
- Load Table 2 – Multiplier for Ball to Car Rear Axle Load
- Load Table 3 – Moving Items in the Trailer to Change the Ball and Trailer Axle Load
- Load Table 4 – Moving Items in the Car to Change Car Axle Loads
These can be found at https://campandtravel.com.au/calc3.html. 
It is important that you note and agree to the ‘Disclaimer’ below.
Some Help Before You Start
In a series or blogs and videos I posted on this webpage, I have stepped through the experience of having my car and camper weighed, and subsequently exploring how loads affect the tow vehicle and trailer depending on where they were carried.
As such, I recommend that you have a look at these first, or after, you set out to understand the results of these calculators.
- https://campandtravel.com.au/what-is-tow-ball-weight/
- https://campandtravel.com.au/towing-anything-outabout-with-dayv/
- https://campandtravel.com.au/ball-weight-calculator/
How to Use the Calculators
Load Table 1 – Ball to Car Rear Axle Load
Description: This calculator looks at the car’s wheelbase, the distance from the rear axle of the car to the ball on the hitch and the actual or proposed load on the ball from the trailer.
Result: The result of the calculation is the impact that this ball load will have on the car’s rear axle. By using it you will see that a 250kg load on the ball will be more than 250kg on the axle due to the lever effect of the hitch’s overhang behind the axle. How much will depend on the overhang and the wheelbase.
Use: If you are looking to buy a new trailer, you ought look at the car’s axle load capacities as well as the tow ball limits – remembering that the car’s axle already has a load on it. Similarly, if you are moving loads on the trailer you should be aware of their impact on the ball load and the car’s axles. You could also use this calculator when comparing possible tow vehicles.
Load Table 2 – Multiplier for Ball to Car Rear Axle Load
Description: This calculator looks at the same measurements as Table 1. By knowing the car’s wheelbase and the hitch overhang, you can determine a multiplier for your car.
Result: The result will be a number greater than 1 and can be thought of as a percentage increase.
Use: By knowing your car’s multiplier, you’ll be able to use it as a ready reckoner or for quick comparisons. For example, I know that my car’s multiplier is 1.47 – so if I have a ball load of 100kg, that would be an additional load on 147kg on the car’s rear axle.
Load Table 3 – Moving Items in the Trailer to Change the Ball and Trailer Axle Load
Description: This calculator asks for the load of the item you are adding or removing (show as negative). Then, by knowing how far the trailer axle is from the ball and where the item is to be added or removed, the impact of the change on the ball load and the trailer axle can be calculated.
This calculator also allows you to use your car’s multiplier (determined from Table 2 above) to see what may be the impact of these changes on your car’s rear axle.
Result: There are two results. The first is the impact on the trailer ball load and the second is the impact on the trailer axle.
By applying your car’s multiplier (determined from Table 2 above) the impact of these changes will be displayed for the car’s rear axle.
Use: By simply adding or removing an item, the loads and dynamics of the trailer will change – as will their impact on the car. If you are removing something to place it somewhere else on the trailer, you will need to do one calculation to remove the item and another to add it. Similarly, if you are adding / removing multiple items, you will need to do each individually and keep a seperate tally outside the calculator. By adding your car’s multiplier to the calculator, you will be able to see the resultant impact on the car’s rear axle.
Load Table 4 – Moving Items in the Car to Change Car Axle Loads
Description: Just as Table 3 provided some insight into how removing or adding items somewhere in the trailer can make a difference, Table 4 allows you to see the impact of removing or adding items in, and on, the car itself.
Result: The impact on both the car’s rear and front axles are displayed.
Use: This calculator can be used when considering where to place loads in and on the car. For example, adding a winch on the front bull bar will add weight to the front axle, while moving say a spare tyre mounted on the roof rack from the rear to the middle of the car will reduce the load on the rear axle and place more load on the front axle.
Much of this is very iterative and needs to be repeated as you explore the what-ifs for your situation. By this, I mean if you reduce the load on the car’s rear axle by moving loads in the car you may be able to revisit the loads from the ball of any trailer – and if you change your ball loads you may need to revisit how you pack the car.
Check Your Numbers and Know Your Actuals
As I found out when I was told that my loads were ‘sailing close to the wind’, you can be left bamboozled and feeling alone – and worse still thinking that you’ll get away with any limits being exceeded.
Just remember that, if you have an accident or mechanical failure, your holiday can quickly turn to custard and those around you could be severely impacted. Not to mention the attention your car and trailer will draw from the police, insurance companies and lawyers.
You owe it to yourself and your family to explore the numbers and to keep safe.
Play with the calculator and see what you can come up with. But, you do need to get weights and loads from driving over a weigh bridge or from those who can tell you your actual weights.
Disclaimer
The results shown in these calculators are purely mathematically derived and do not take into account the many variances that can occur in the real world of cars, trailers, travel speeds and road conditions. As such, these calculators should be used only to determine what-if scenarios in the broadest sense and should always be followed up with actual weights taken at recognised weigh bridges. You are responsible for the loads you carry and for understanding the capacities and capabilities of your vehicle and trailer – and yourself. If in any doubt ask an expert in the relevant field.
