Caravan Towing Weights Explained: ATM, Tare & GVM

Understanding weight limits and specifications when towing a caravan is vital for safety, legal compliance, and optimal road performance. Three key terms are used regarding caravan weights: Tare weight, ATM (Aggregate Trailer Mass), and GVM (Gross Vehicle Mass). These terms play a crucial role in ensuring that your vehicle and caravan are correctly matched for safe towing. Here is a guide to understanding and managing caravan weights.

Why are caravan weights important?

Ensuring the weight of your caravan, tow vehicle, and their combination is essential for: 

• Safety: Overloading either vehicle can compromise braking, handling, and overall stability, resulting in dangerous driving. 
• Legal compliance: Exceeding the GVM or ATM can lead to fines and legal issues. 
• Warranty: Overloading your vehicle can void your warranty.

Caravan weights summarised

In summary, the Tare weight helps determine how much load can be safely added, the Aggregate Trailer Mass (ATM) prevents the caravan being overloaded, and the GVM (Gross Vehicle Mass) ensures the towing vehicle can handle the load's weight, preventing unsafe towing conditions. But it's worth knowing what each is in more detail and why it matters.

The Tare weight of a caravan

The Tare weight of a caravan refers to the weight of the caravan when it is empty—without any contents like water, gas bottles, personal belongings, or passengers. However, it does include built-in fittings, fixtures, and appliances. 

• Why it's important: The Tare weight is critical for understanding how much weight your caravan will add to the total weight of your towing setup. It's a base weight from which the maximum allowable weight (the ATM for caravans and the GVM for tow vehicles) is calculated. Understanding the Tare weight will also help you choose a towing vehicle capable of safely towing your caravan if you’re new to caravanning. 
• Where to find it: The Tare weight is usually found on the vehicle plate or in the manufacturer's handbook.

What is the kerb weight?

You may also hear the term kerb weight. This is essentially the same as the Tare weight, but there can be subtle differences depending on regional terminology or the specific context.

Aggregate trailer mass (ATM)

What is ATM weight on a caravan? The ATM is the total weight of the caravan when it's fully loaded, including water, gas bottles, cargo, and personal belongings. Essentially, it's the maximum permissible weight of the caravan (the 'payload') when it's ready to hit the road, including the caravan's own weight (Tare weight) as well as anything else carried in the caravan. 

• Why it's important: This weight is critical because exceeding the ATM can lead to instability, dangerous handling, and can be illegal, as it may violate the towing regulations set by government and local authorities. Exceeding the ATM could also mean you are not covered by insurance in the event of an accident. 
• Where to find it: The maximum permissible ATM for your caravan can be found on the compliance plate, which is usually located near the VIN number, the caravan's door, or in the caravan's manual.

How to determine caravan weight

If you are unsure about your caravan's weight when it's fully loaded, you can take it to a public weighbridge to get an accurate reading of its current weight. This will allow you to calculate how much load you can still add safely. There are also a number of apps that can help, including LoadMate. Check out our caravan apps blog for more info.

Caravan GVM (Gross Vehicle Mass)

The GVM is relevant to the towing vehicle, but it’s not the same as the towing vehicle's actual weight. It refers to the maximum weight the towing vehicle (not the caravan) can safely carry, including the vehicle itself, fuel, passengers, cargo and the weight exerted by the caravan on the tow ball (the Tow Ball Mass TBM—more on that below). 

• How to calculate it: Find the Manufacturer's GVM Rating—this is not something you calculate; it is set by the manufacturer. It is usually listed on the vehicle's compliance plate or in the owner's manual. 
• Why it's important: If you exceed your GVM, your tow vehicle may struggle to perform correctly, especially in terms of braking, handling, and acceleration. This can lead to safety hazards, including poor vehicle control or even mechanical failure. Exceeding the GVM can also lead to fines, issues with vehicle insurance, and even voiding your warranty.

Other weight-related terms

Other terms you may come across when it comes to caravan weights include: 

• Caravan tow ball weight: Also known as Tow Ball Mass (TBM), this refers to the vertical load that a caravan exerts on the tow bar of the tow vehicle. It's essentially the weight of the caravan pressing down on the tow ball. 
• Gross Trailer Mass (GTM): This is the weight of the caravan when it's fully loaded and ready to travel. It includes the weight of the caravan itself (its Tare weight) plus the weight of all the contents inside, including food, water, equipment, furniture, and any other items you've packed for the trip. 
• Gross Combination Mass (GCM): This is the total combined weight of the towing vehicle and the caravan or trailer when they are fully loaded. It's the maximum allowable weight of both the vehicle and the caravan, including everything inside both. This is the figure you’re aiming for!

How to safely tow your caravan

Understanding basic terms like Tare, ATM, GVM, TBM and GCM is vital for ensuring you stay within legal weight limits and maintain safety on the road. Lots of abbreviations we know, but they're worth knowing! 

Another tip is to always check that your caravan is loaded correctly and that the weight is distributed evenly to avoid instability. Ensure the tow ball is securely attached, the brakes and lights on the caravan are functioning, and the safety chains are correctly connected. 

Regularly check tyre pressures, including both the towing vehicle and caravan. Drive with caution, allowing extra braking distance, and avoid sudden lane changes or sharp turns. Always stay within the legal speed limits, and remember that reversing with a caravan requires practice, as the combination behaves differently from a solo vehicle. Safe towing also means maintaining a clear view of your mirrors and properly balancing the caravan for optimal control.