Caravan and Tow Vehicle Towing Capacity

When it comes to towing a caravan, there is definitely more than meets the eye involved in the process. To an outsider it looks simple enough, but any seasoned caravanner knows that it can get very complicated.

Working out your towing capacity is not just a matter of practicality – it is also required under law that you keep safe on the roads. Here’s how you can work it all out and understand the measurements involved, so you can tow safely and stay on the right side of the law.

Know your lingo

Let’s start with a few of the key terms and words you will need to know when looking into towing. It can sound like nonsense to start with, so this will help you to get a grasp of the meaning behind mystical weighing instructions!

  • Tare mass: this is the mass of your vehicle or caravan with nothing in it. For your tow vehicle, this is how much it weighs at the manufacturer specification and will include fuel and coolant. For your caravan, it also goes by manufacturer specification. In both cases, you do not include any payload.
  • ATM: short for aggregate trailer mass, this is calculated by adding the tare mass of your caravan to your maximum payload. This rating is set by the manufacturer and it is against the law to exceed it.
  • GVM: gross vehicle mass is the limit of weight that your car can support, including your car, your passengers, and your tow ball mass. Again, this is a rating set by the manufacturer that you cannot exceed by law.
  • GTM: gross trailer mass is the same as above for your caravan. It does not include the portion of the weight which will be supported by the tow bar or the jockey wheel.
  • Payload: this is any mass which you add to your vehicle or caravan. Think about passengers, luggage, bull bars or other features put on as aftermarket additions, and tow ball mass.
  • Maximum payload: unsurprisingly, this means the maximum weight that you can add into the vehicle or caravan on top of the tare mass. With your caravan, you don’t need to include passengers who will be using the caravan after you park up, but only what will be inside when you are on the road. It does include water and gas and anything you have put into the caravan for transport.
  • TBM: tow ball mass is the mass which is exerted on the tow ball once your caravan is ready to go. When you hitch up, the TBM is included in your two vehicles’ payload, which is why you need to calculate it carefully.
  • GCM: combine the maximum gross mass of your trailer and your vehicle and you will get your gross combined mass.
  • TBD: tow bar download is the amount of pressure that the tow bar can handle. Usually, it should be between 10 to 15% of your GTM.

Do your sums

To recap, here are the sums you are going to need to know:

  • ATM = caravan tare mass + caravan max payload
  • GVM = vehicle tare mass + maximum payload
  • ·Maximum payload = ATM – tare mass – tow ball mass
  • GTM = ATM – tow ball mass
  • GCM = GTM + GVM
  • TBD / GTM x 100 = % of GTM

Know your vehicle

Some of the equations have been done for you. Your tare, ATM, TBM, and GTM will be stamped on the VIN (vehicle identification number) plate of your vehicle. This will make it a bit easier for you to get started. A lot of the other numbers can be found in your owner’s manual and documentation for both your vehicle and your caravan.

You can also use a public weighbridge to figure out the exact weight of your vehicle when you are all packed up, to check your caravan weight, and to find out the weight of both together.

Calculating the numbers is really important because overloading either your caravan or your car could prove to be dangerous on the roads. You can’t simply go by your vehicle’s recommended legal towing capacity because when you increase your GVM, you will have less room in your GCM for the caravan.

Another thing to consider is that weight should be distributed as evenly as possible between the front and rear axles of your vehicle. This is to help distribute the pressure across the car, rather than putting it all down through one set of wheels. If you have a heavy caravan to tow, you might not want to load up the back of the car with heavy items as well. You may even have to think of it in terms of having your heaviest passenger sit in the front seat.

Know the consequences

Technically, there may be occasions when you are able to load your caravan up heavier than the recommended tow limits and still make it to your destination. Should you?

The legal answer is no. The logical answer is also no, because you will be putting yourself in danger. Even if you do not believe there is much of a risk, you should still be aware of the potential legal consequences.

In a worst-case scenario, you may end up crashing because of your overloaded caravan and tow vehicle. If you do, there is a good chance you will involve another vehicle in the accident, especially on busy roads. Should another person die as a result of the crash, and it is shown that you knew your caravan was overweight, you could be brought up on charges of dangerous driving occasioning death.

If you are caught during a random check or a non-fatal accident, there are still legal consequences to bear. You may be asked to pay a fine and you may also find that your insurance claim is refused. Further legal action could also result.

The capacity of your towing vehicle may take some work to figure out, but it could save your life or someone else’s if you make those checks. Never tow a caravan which exceeds your GCM, or you could face serious legal consequences.



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