Ball Weight, GTM & ATM Explained – Understanding Your Offroad Grit Specs

To reach peaceful destination you need the piece of mind that your setup correctly to tow!

When you're investing in a tough, reliable off-road caravan like the Offroad Grit, understanding key towing terms is essential—not just for compliance, but for safety, performance, and peace of mind. Terms like Ball Weight, GTM, and ATM can sound technical, but they’re the backbone of safe towing and have a direct impact on how your caravan handles on and off the road.

In this post, we’ll break these down in plain language and explain how they apply specifically to your Offroad Grit van.

ATM (Aggregate Trailer Mass)

What it is: The ATM is the maximum total weight of your caravan when fully loaded, and not hitched to your vehicle. This includes everything—water in tanks, gas bottles, gear, food, and any aftermarket additions.

Why it matters: The ATM is your legal limit. You can’t load your caravan beyond this number, and it helps determine what vehicles are suitable for towing your van.

Offroad Grit example: If your Offroad Grit has an ATM of 4,500 kg, that’s the absolute maximum weight the van can be when loaded and unhitched.

Ball Weight (Tow Ball Load)

What it is: This is the portion of your caravan’s weight that’s transferred to the tow vehicle’s tow ball when hitched up. It’s typically measured when the van is fully loaded.

Industry standard: Most vans aim for a ball weight of 10–15% of the ATM. For a 4,500 kg ATM, that’s around 450 kg—which is what Offroad Grit vans are engineered around.

Why it matters:

• Too little ball weight = instability and sway

• Too much ball weight = overloaded towbar and poor handling

At Offroad Grit, we set our ball weight based on engineering best practice to ensure a stable, safe towing experience.

🚙 GTM (Gross Trailer Mass)

What it is:

GTM is the total weight of your loaded caravan when it’s hitched to your tow vehicle—in other words, the ATM minus the ball weight.

Using our example:

• ATM = 4,500 kg

• Ball weight = 450 kg

• GTM = 4,050 kg

Why it matters:

The GTM tells you how much weight is actually on the caravan’s wheels. It must be within the rating of the axle, suspension, and tyres.

Compliance Plate includes all information such as Ball weight, GTM, ATM

Why We Don’t Adjust GTM or Ball Weight

We’re often asked if the GTM can be increased or the ball weight reduced—but the answer is no. Here’s why:

• Increasing GTM would decrease the ball weight, which can lead to sway and poor towing stability.

• Reducing ball weight below engineered specs compromises safety and handling, especially on rough or uneven terrain.

These values are carefully calculated and tested to meet safety standards and deliver dependable off-road performance.

Tips for Keeping Ball Weight in Check

• Store heavier items forward of the axle, not at the rear.

• Travel with water tanks full or empty, depending on their position.

• Use a ball weight scale to measure accurately before hitting the road.

  

  Ball Weight Scale

  
  

Final Thoughts

Understanding your caravan’s towing specs is essential for a safe and enjoyable trip. At Offroad Grit, we've taken the guesswork out of it—our builds are designed with optimum weight balance and road performance in mind.

If you have any questions about your specific setup or need help understanding your compliance plate, feel free to get in touch with our team. We're here to help you hit the road with confidence.