Watch Your Weight: Mass-Related Towing Terms You Should Know

trailer partsTowing involves a lot of physics; unfortunately, not everyone loves a dose of math. Numbers can get confusing and it’s just not the kind of thing you would want to think about when you’re going on an RV trip with the family. Every caravan enthusiast, however, knows that you have to understand certain weight-related terms to tow things right.

Fortunately, you don’t have to sweat all the numbers. A1 Trailer Parts explains these terms for a better and safer towing experience.


ATM stands for aggregate trailer mass, which means the overall recommended maximum load of the manufacturer. ATM is the term for the entire weight capacity of the vehicle, including everything that it has to tow such as luggage, water, etc. When computing this, you have to include the mass resting on the van’s wheels and the mass that’s on the towbar. Whatever you’re carrying, the total weight shouldn’t exceed this figure.


Gross trailer mass is almost similar to ATM, although this one always has a smaller figure. While the ATM includes everything, the GTM excludes the weight that rests on the towbar once it’s linked to a tow vehicle. The GTM focuses more on the weight that’s on the rig’s tyres and also indicates the maximum load the manufacturer recommends.


Also known as the “empty” weight, this is the van’s mass fitted with all OEM equipment minus your personal luggage. In other words, this is the actual weight of the van the moment it left the production line.

Load-carrying capacity

Load-carrying capacity is sort of the legal term in towing. This pertains to the total permitted weight you are allowed to carry in the van – food, luggage, water, and similar items. You can get the load-carrying capacity by subtracting the tare from the ATM. Accessories that you don’t include in the tare would reduce your load-carrying capacity for personal effects.

Ball weight

Also known as ball load, this pertains to the force applied on the tow vehicle’s towbar. This figure has to be somewhere between 8-15% of the ATM all the time.

When you understand these terms, you will have a safer and more convenient time caravanning. Use the numbers to your advantage and enjoy your next adventure minus all the weight-related trouble.

About the Author

As a New York-based psychologist. Thelma Scott has conducted several seminars tackling adult autism.