Your car and tow bar has a maximum tow ball weight. Whichever is the lesser, is the maximum amount of load you can place on your tow bar when hooking up a trailer (caravan, camper or box).
But, what does that weight really mean when you look at the bigger picture of loads on the tow vehicle (sometimes called the ‘tug’).
Luckily, we can turn to Archimedes (born in 287 BC) and his teachings in regard to levers.
Imagine if you had a shovel of dirt with the handle horizontal, and the top end of the shovel was fixed in place. If you wanted to lift that dirt, its load would be ‘increased’ depending on where you held the shovel – but it will always be heavier than the weight of the dirt itself. This is known as a ‘third-class’ lever.
In the same way, the front of your car can be considered as being fixed, the rear axle of the car as the point where you hold the shovel and the load on the tow ball as the dirt.
The affect of this lever on the load at the axle is a proportion of the car’s wheelbase (the distance from the Front Axle to Rear Axle) and the overhang of the tow bar behind the rear axle (the distance from Rear Axle to Tow Ball).
To continue the analogy with the shovel, if you move your hand towards the dirt it will become easier to lift; and if you try to lift nearer the fixed end of the handle it will be much more difficult.
We can see then too, that:
The trick to using my quick axle load calculator is to know:
Even if you don’t know these actual loads, you can still have a fiddle with some hypotheticals to see how your car loads are affected by these ‘levers’.
As you will soon see, 350kg on the ball can be significantly more when you look at its affect on the rear axle. This may be an amount greater than what you have left to play with in a loaded car.
The calculator also gives you a multiplier for your car that you can use as a quick ready-reckoner in your head.
You can even use this calculator as a tool when doing your research before you buy a new car or trailer.
Please let me know how you go. I’ll be interested in your feedback.
Disclaimer – You need to do your own research and enquiries that this calculator works for you and your circumstances before making any decisions. You should always check your loads by visiting a weighbridge or having them professionally weighed.