RVers commonly wonder, “Can a motorhome tow a caravan?”. Although this is not a common sight in Australia, its legality depends not on the type of trailer to be towed, but primarily on the overall towing capacity of the motorhome-caravan combination. See the example below for further details.
Components in a motorhome-caravan tow combination
To give you a better understanding of what is to be discussed later on, you must be familiar with the major components. You can find an illustration of these items below.
What does “overall towing capacity” mean?
Going back to our primary answer above, our main concern here is to determine the overall towing capacity. This is because the overall towing capacity is the appropriate benchmark that determines whether or not your towing setup is allowed.
In straight terms, the overall capacity is the value that is the least of five figures, namely
- Motorhome GTM (Gross Towing Mass) – the maximum weight of the (hitched) trailer allowed by the manufacturer
- Tow ball and Tow coupling capacity – Maximum allowable rating for 50mm ball/coupling is 3500kg
- Caravan (or trailer) GTM (Gross Trailer Mass)
- Drawbar capacity – This is always higher than the Caravan GTM rating
- Tow bar rating
Most light vehicle manufactures will specify the maximum tow ball download weight. This amount is usually around 10% of the towbar maximum rating. However, this is set by the manufacturer and can not be exceeded even if the above items suggests a higher rating is capable.
What factors must be considered when towing a caravan?
Towing capacity takes into account many considerations when determining the tow rating. Vehicle gradability, braking performance, major component ratings, vehicle handling characteristics to name just a few. Just as a person is not recommended to carry things that are heavier than him/her, the same goes for vehicles. However, in the case of determining the combinations’ towing limits, there are five main factors to be considered.
1. Towing capacity of the motorhome
This value is set by the motorhome/vehicle manufacturer. This towing capacity is the maximum weight that the motorhome is allowed to tow. The problem sometimes is that it is not directly labelled as “towing capacity”. Rather, you would find terms such as GVM, GTM and/or GCM.
- GVM (Gross Vehicle Mass) is the maximum total weight your motorhome is allowed to carry.
GVM = tare mass + payload
- GTM (Gross Trailer Mass) is the maximum allowable weight of the entire trailer when hitched.
GTM = trailer tare mass + trailer payload
- GCM (Gross Combination Mass) is the maximum weight that the motorhome-coupling-caravan combination can not exceed.
GCM = GVM + GTM
- Payload is the maximum allowable weight for all the vehicle’s passengers, luggage and all accessories. Some accessory examples are your camping gear, bike, towbar assembly, tow ball, and drawbar assembly.
To know more about the definitions of the weight terminologies described above, check out this blog.
More often than not, your manufacturer provides either a GVM-GTM or a GVM-GCM combination. The point is, aim to get the GTM using the formulas above.
2. Tow ball and tow coupling capacity
It is an Australian Standards and ADR requirement for labelling of the tow ball and tow coupling is provided. This is usually in the form of embossed characters in the coupling body or stamped on the ball. Keep your tow ball and tow coupling capacities noted for comparison later.
3. Towing capacity of the trailer or caravan
Similar to motorhomes, this value is set by the trailer manufacturer and is known as the GTM. It is different from ATM (Aggregate Mass Trailer) in that the latter refers to the trailer’s maximum allowable weight when unhitched.
All caravans are trailers but not all trailers are caravans.
4. Drawbar capacity
As part of the caravan manufacturers’ requirements, they must ensure that the drawbar that is fitted to the caravan is suitable for the rating of the trailer. The drawbars must have a safety factor built into the design of the structure and is rated higher than the ATM.
5. Towbar rating
Being the component that connects between, the tow vehicle and the tow ball and coupling this sometimes is lower than the rated tow ball and coupling. Therefore, its capacity must be considered as well. Look for this value in its label which is usually in the form of a rating plate or sticker on the towbar.
Whew! That was quite a long list. So, what now? After having obtained the four values above, (we can exclude the drawbar rating), compare them and get the least value. That is now your maximum overall tow capacity which you should follow. As promised, I have an example for you to base on.
Calculation example for a motorhome towing a caravan
Your motorhome VIN plate displays the following data:
- GVM = 3500 kg
- GCM = 6000 kg
You have found your tow ball to have a maximum tow capacity of 3500 kg. The caravan that you want to tow is rated at 3000kg. Your caravan VIN plate shows:
- GTM = 3000 kg
- Tare mass = 1800kg
You noticed that your towbar label displays a maximum tow capacity of 2500kg. And finally, your tow coupling label shows a maximum tow capacity of 3000kg. What now is your overall maximum tow capacity?
- Motorhome GTM = GCM – GVM = 6000 – 3500 = 2500 kg
- Tow ball capacity = 3500 kg
- Caravan GTM = 3000 kg
- Towbar capacity = 2500 kg
- Tow coupling capacity = 3000 kg
Comparing the five values above, the least value is 2500 kg which is your overall maximum tow capacity. Now here’s a follow-up question: Since your caravan, GTM is higher than the overall maximum tow capacity, does that mean that you’re not allowed to use your caravan anymore?
The short answer is no. You may still use your caravan BUT you have to lessen the amount of luggage and accessories that you are to put in your caravan (i.e. payload). If you’re wondering, “by how much?”, here’s the solution:
GTM = tare mass + payload
Payload = GTM – tare mass
If we were to consider only the caravan’s GTM, the payload would be:
3000 – 1800 = 1200 kg
However, since we determined our “final” limit to be 2500kg, the new payload would now be
2500 – 1800 = 700kg
That means, instead of 1200kg, you have to limit your caravan luggage and accessories to 700 kg.
Where can I find the GVM, GTM, GCM, etc.?
These values should be available in your Operator’s manual (in both motorhome and caravan) and your VIN plate. Also, you can find some of these values in the label of your towbar, drawbar and tow coupling.
Australian Design Rule (ADR) 61/03 states that, effective 10 December 2019, all trailers (i.e. caravans) must include in their VIN plates both the GTM and ATM (Aggregate Trailer Mass). Hence, consult your manufacturer if any of these details are missing.
Calculating and determining towing capacities may be confusing at first. But as you understand the concept combined with a little bit of practice, you will get the gist of it. So to conclude, a motorhome is allowed to tow a caravan provided that it is within the overall maximum tow capacity of your motorhome-caravan combination and the dimensional requirements.