Is ATM and GVM the same? (the weight of a caravan explained)

In this guide, we explain whether ATM and GVM are the same and other important terms related to the weight of a caravan you should know. We also describe what happens if you exceed the towing capacity and how to correctly load a caravan to be safe on the road.

Is ATM and GVM the same?

No, ATM and GVM do not stand for the same terms when speaking of caravan weight. 

ATM (Aggregate Trailer Mass) is the total weight for which the vehicle is authorized, including its Tare, and therefore that the vehicle must not exceed. For example, if your caravan has a tare of 1,250 kg, and a GVM of 1,300, you can ONLY add 50 kg to the factory weight. 

Beware that in that 50 Kg are the air conditioning, the spare wheel, the antenna, the television, the kitchenware, the gas cylinder, the food, the clothes! Don’t you think you’ll get over it? Well, it is something that happens and more than you can imagine.

GVM (Gross Vehicle Mass) is the maximum laden mass of a caravan/motorhome while driving on the road. The GVM is usually specified by the Manufacturer. 

The weight of the caravan explained

The weight of the car plays a very important role: The heavier it is, the better it can handle the caravan. Or put another way: The more the difference in weight between the tug and the trailer in favour of the former, the better. 

These differences are especially important during braking, hills and slopes, or strong winds. The tugboat must dominate the trailer, never the other way around. 

Let’s see if I can make myself understood. We must be clear about some concepts before buying a caravan, at least the most important ones. Sometimes they can confuse us, as it happened to me at the beginning. All of them are very important and we must know them if we aspire to buy a caravan and travel with it.

Tare – Tare is the “unloaded” weight of the vehicle, that is, the minimum weight of the vehicle, ready to drive with its authorized fixed equipment: fuel, lubricant, brake fluid, spare parts, tools and other mandatory accessories. Without driver, passengers or cargo.

MiRO (Mass in Running Order) – is the same as Weight in Running Order. It is the Tare plus the weight of a standard driver of 75 kg. Our personal belongings and/or extras from the caravan that we add later do not enter the MiRO calculation.

MAM (Maximum Allowable Mass) – Maximum Allowable Mass. It is also called Maximum Authorized Weight. It is common for manufacturers to adjust it a lot. In other words, it is very common for the MMO (Mass in Marching Order) of the caravan to be just a little lower than its MAM. For example, the MMM of the caravan is 1200 kg and its MAM of 1300.

That means that we would only have 100 kg of Payload, that is, what we would have left to add extras and load our things (a little further down we expand this concept). The MAM is the maximum that the vehicle can weigh with its additional equipment, extras, luggage, etc. Exceeding the MAM is grounds for a traffic penalty.

MTM (Maximum Towable Mass) – The Maximum Towable Mass concept is the same as the so-called Maximum Towable Weight. That is the maximum weight that a vehicle can tow.

MJM (Maximum Joint Mass) – MJM = Maximum tug + trailer weight. It is the maximum that our car + caravan set can weigh.

Useful load – This is a very important piece of information when buying a caravan. Before acquiring our caravan we must take into account that the Payload is sufficiently large for the extra equipment that, if necessary, we want to add as soon as we buy it or later.

For example air conditioning, moving (with its battery), awning, tv stand, spare wheel, etc. And of course, the Payload also includes “our things” (clothes, dishes, table, chairs, TV, toys, bedding, microwave, bicycle, food, drinks, etc etc).

We can load whatever we want, as long as the weight of the caravan does not exceed its Maximum Authorized Mass (MAM).

The payload explained – The Dethleffs C’go 495 QSK caravan has a GVW of 1,300 kg and a MiRO of 1,130 kg, therefore a payload of 170 kg (remember that MAM (1,300 kg) – MiRO (1,130 kg) = Payload (170 kg) That means that no matter how few extras we put on it and little luggage we take with us, we will easily go over 1,300 kg.

Among those extras we can find the moving with its battery – an almost essential accessory in medium-large caravans that weighs around 80 kg depending on the models and brands – or the air conditioning, also almost essential in summer in different places, which weighs another 30 kg. A complete advance can weigh more than 30 kg, the spare wheel about 20 kg …

And we need to add what we take with us on a trip: clothes, bicycles, table, chairs, plates, pans, sheets, cleaning products, food …

In short, we adjust the weight very well or we will have no choice but to increase the MAM of the caravan, which is possible in most models, as long as we do not exceed the MiRO of the vehicle. That is why it is important to consider before buying a caravan that the one we choose has a very good payload, or that we have the possibility of increasing it without exceeding the MJM of our car.

Other questions you may be interested in

How much torque do you need to tow a caravan?

How much weight can a caravan chassis take?

How quickly do caravans depreciate?

What happens if you exceed the GVM?

If you only overload your car a lot in specific situations, such as on vacations or exceptionally or occasionally, you do not have to worry about its mechanics especially. It is important to check the car before a trip and not skip the recommended revisions to avoid breakdowns and improve its durability. 

Another thing to keep in mind is to consider the option of taking out travel insurance which includes delays, luggage and assistance to people.

When a car suffers in its systems and parts, it is when you often use it to carry a lot of weight. Some parts are especially vulnerable to this type of situation. If you regularly use your car at the MAM limit, then pay special attention to the state of:

• Tires
• Suspension
• Break system
• Engine
• CO2 emissions increase.

Dangers of exceeding towing capacity

When you carry your car heavily loaded and at the limit of its allowed load – you should never exceed it -, keep in mind that there are big changes that you must take into account and that affect both the way you drive and the mechanics of your vehicle.

• Increased stopping distance. – It is necessary that when you travel with more weight in your car, you increase the safety distance with the car in front of you, redouble your attention and slow down. Your braking system will not work the same as when you usually drive, it will take longer and you will go faster before you stop.

• Decreased stability and balance – The weight makes your car less agile and less balanced, especially if you carry a lot of weight in the trunk, in the rear, if you have a roof rack, a trailer or any other accessory to carry more cargo.

• Increased consumption –  Always keep in mind that if you go with your car at full weight, you are going to spend more gasoline or diesel -also the autonomy in the case of an electric car decreases- so it is worth making an effort to implement the classic tips to reduce the consumption: smooth, careful driving and limited speed. 

In the same way, think about the cost of fuel when you are preparing suitcases and try to minimize so that the weight of the load is as tight as possible.

Plan carefully your trip. If you are going to travel with weight, it is better not to improvise on the way to go. Take advantage of new technologies to choose the most suitable route for a loaded car: avoid mountain passes, large slopes … in general, opt for highways or motorways to increase your safety and improve consumption, when you drive with a car with maximum weight.

How to correctly load a caravan?

If the vehicle does not have much space to carry things and it is necessary to load the caravan, it will always be done in the centre and on the axle. Placing the load in the front will result in an imbalance resulting in the vehicle sinking through the rear suspension. This will cause the front axle to lift and lose steering.

In the same way, as is known, tow balls do not allow a lot of weight vertically. In a normal car, the weight that the tow ball can support is not much more than 70 kilograms. In the case of caravans, if you want to know the vertical weight they support to travel safely, you just have to look at the plate of the tow ball. However, reaching the weight limit is not good.

If what we do is to load the part behind the caravan a lot, the danger increases, since the part behind the vehicle will end uplifting and it will be totally unstable.

For all these reasons, the front chest should not support a lot of weight, although currently, caravans have a large chest, even with the possibility of placing two large butane or propane cylinders in it. However, it is recommended to carry them in the trunk.

It is important not to have a lot of weight on the drawbar because not only will the tow ball be overloaded, but also the stabilizers will not be able to support a lot of weight because they are not designed for it.

Lighter objects such as kitchen towels or towels can be carried in the mezzanine cabinets. However, it is better not to overload this part too much, since weighting such a high position ends up raising the point of gravity and it is easier to overturn.

In the event of an imbalance, what to do is stop and re-house the load in the best possible way.

Final thoughts

In this article, we explain the difference between the ATM and GVM when speaking about the weight of a motorhome. We described what happens if you exceed the towing capacity and how to correctly load a caravan to be safe on the road.

To summarize, ATM (Aggregate Trailer Mass) is the total weight for which the vehicle is authorized, including its Tare, and therefore that the vehicle must not exceed. And GVM (Gross Vehicle Mass) is the maximum laden mass of a caravan/motorhome while driving on the road.

If you have any questions or comments on the content, please let us know.

FAQ  on Is ATM and GVM the same?

References

Towingandtrailers.com

Caravanchronicles.com

Practicalcaravan.com