How To Calculate Your Towing Capacity

If your buying your next car with the intention to tow, it is vital that you are fully aware of it's capacity to tow, and what influences the actual weight.

When choosing a car to tow with you, you need to consider and include all weights, including not only the weight of the car when fully loaded, but all the accessories fitted. We often think about the weight of the bull bar or the canopy, but what about the weight of the floor mats, car seat covers and other small add on's? Each of these individually might only be 4 or 5 kilos, but when all added up together, could be 20 kilos or even more. Also, if you've changed from the factory alloys and road tyres to steel rims and off road tyres, these will easily add another 20 kilos to the weight of the car. Don’t forget to include a full tank of fuel, passengers, luggage, and once a trailer is connected, the towball weight of the trailer is also then measured as part of the vehicles weight.

As you can see, there is more then meets the tow ball: here is handy guide on how to calculate your towing capacity.

CALCULATION

Towing capacities are calculated by a number of maximum weight limits. The three most important numbers for you are Gross Vehicle Mass (GVM), Gross Trailer Mass (GTM), and Gross Combined Mass (GCM). In short, the GCM must be less than the sum of the GVM and the GTM combined. But in the case of towing, one plus one does not always equal two...

Let's take one of the most popular towing vehicles, the Toyota HiLux. It has a maximum GCM of 5650kg, but its GVM is 3000kg and its claimed GTM 3200kg, which adds up to 6200kg - 550kg more its GCM. That's because in its GVM, the manufacturer is considering a full payload of 955kg (the maximum for the HiLux). Since you're 550kg over, you actually only have 405kg left before you reach the maximum towing capacity - approximately the weight of all your camping gear combined. But then you won't have a kilo left for any added accessories or even a carton of beer.

If you're buying a tow vehicle, look at its GCM. Deduct its GVM. Now deduct the weight of any accessories and everything you're carrying and you've got your GTM. In case of the HiLux: 5650kg minus 3000kg = 2650kg. If you don't have anything bolted on your vehicle, and aren't carrying anything else, that's the maximum weight of your trailer, caravan or camper trailer.

FINE PRINT

Don't think that just by adding up the numbers everything will be all right. There are more rules you should know before hitting the road. Does the weight of what you're towing exceed 750kg? Then it needs its own electric brakes. On a car licence, you can only drive a vehicle with a GVM of up to 4500kg, and if you buy a trailer that's too heavy for your car, the person or dealer selling it is essentially breaking the law in selling it to you.

Also take into consideration that what you're towing cannot be heavier than the maximum rate capacity of your tow bar and coupling. You also cannot carry passengers in your caravan when towing, in case you were wondering.

TRAILER

Make sure that any trailer you are going to tow is going to weigh less than the maximum tow rating of the vehicle variant you are driving.

In the case of some vehicles, the tow rating of the actual vehicle can change based on the specs of the vehicle; if it is a petrol or diesel, 2WD or 4WD, Auto or Manual for example. Once you know the rating of the vehicle,  make sure the tow rating of the tow bar fitted to the vehicle is also suitable as the lesser of the two, vehicle or tow bar, will be the limit. Also ensure that once the trailer is loaded that the actual measured tow ball weight does not exceed the tow ball limit of the vehicle or the tow bar.

Another important weight to think about is the forementioned GCM, this is the maximum weight of the vehicle and trailer combined, once they are connected together and can not be exceeded. The GCM is not always the GVM plus the tow rating added together.  In most cases, the GCM is less than these two figures added together.

CONCLUSION

You need to do the numbers to make sure you comply with all weight limits and are towing in a safe and responsible manner. If you have an accident and need to make an insurance claim, the first thing the insurers do is to check your weights. If your deemed overweight, your claim could be rejected. A manufacturers maximum towing weight might not be conclusive because they cannot take into account all the accessories you've added to the vehicle or what you are towing. Think 100kg for a canopy, 80kg for a bull bar, 40kg for roof racks and under body protection - each - and about 30kg for your winch.

So don't count on any number blindly and do your homework.