Understanding Ratings & Masses When Towing

Understanding Ratings & Masses When Towing

Did you know that working out and understanding Ratings and Masses for caravans remains the Number 1 problem within the RV Industry?

It is a problem common to many caravanners as they set out on their trip, whether full time on the road or just for a short break, fully understanding the rating of your caravan is imperative.  Making sure your caravan is not overloaded is one thing, but matching your van to the right towing vehicle and fully understanding what your vehicle is capable of towing is just as important.

Chances are when you purchased your van, several terms were thrown around.  Things like GTM, Tare Mass, Ball Loading, and ATM, (Which by the way is not where you can find an Automatic Teller Machine)

And whilst many throw these terms around like we should all know them the fact is that it can get confusing.  So this article goes a little way to explain further, in particular, what is considered to be a Rating and what is defined as a Mass.

Caravan Ratings & Masses

The GTM & ATM are Ratings… allocated by the Manufacturer

The Tare Mass and Ball-Loading are Actual Masses… that must be measured

The Tare Mass is the actual measured mass of the vehicle as it leaves the Supplier.
The vehicle is fitted with everything that was stated on the Purchase Contract.
The vehicle is empty. The gas cylinder(s) and the water tank(s) must be empty.
See the diagram below showing the caravan hitched and unhitched and explaining the difference between a GTM & ATM rating.

Drawing 1 shows measuring the “Axle-Loading” MUST NOT exceed the GTM Rating
Drawing 2 shows measuring the “All-Up Mass”  MUST NOT exceed the ATM Rating

The diagram below shows how to work out the Legal Load -carrying capacity

Legal Load-Carrying Capacity = AMT Rating – Tare Mass

The diagram below shows how to work out the Ball Loading capacity

The Ball-Loading is – the difference between the two readings (i.e. Hitched weight – Unhitched weight)

ATM: Aggregate Trailer Mass (Rating)

GTM: Gross Trailer Mass (Rating)

The GTM Rating must not exceed the lowest of the “Axle-Group” Rating

The “Axle-Group” comprises the:

Wheels & Tyres
Suspension Structure
Axles & Wheel-Bearings


GVM: Gross Vehicle Mass (Rating)

GCM: Gross Combination Mass (Rating)

RAC: Rear Axle Capacity (Rating)

Maximum Permitted Towing Capacity: (Rating)

Maximum Permitted Coupling Down-load Capacity: (Rating)

Tow-Bar: Maximum Permitted Towing & Down-load Limits: (Ratings)


Information in this article was reproduced with the permission of The Caravan Council of Australia.  You are welcome to download a pdf version of the original article here.

For more helpful insights into Compliance, Safety, and Quality in regards to the RV Industry, feel free to check out the CCA website @  www.caravancouncil.com.au





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