Perth 4WD and Adventure Show

Understanding Trailer and Vehicle Mass for Safe Towing

Ronny Dahl has been getting his new vehicle ready for towing. Ronny has done his fair share of towing in his time, but usually only a trailer or camper trailer.  With his kids getting older, Ronny is getting into caravanning, and is learning there’s a difference between towing a caravan and a camper trailer – and a lot more to remember. Here’s some tips Ronny has learned from Phil at George Day Caravans and Motorhomes in Perth.

Learning the acronyms!


Most 4wdrivers have heard of GVM but might not be able to explain exactly what it means. GVM – Gross Vehicle Mass – means the maximum your vehicle can weigh when fully loaded as specified by the manufacturer. Your vehicle’s GVM figure will be shown of a weight placard which is found inside the vehicle, usually near the driver’s door. It will also be listed in the owner’s manual. The vehicle’s GVM is the weight of the vehicle, plus all accessories (bull bars, roof racks, winches etc) plus whatever is inside the vehicle – people, luggage etc. If you’re using the vehicle for towing, the GVM will also include the tow ball download.


ATM (Aggregate Trailer Mass) is the is the maximum towing weight of the trailer or caravan as specified by the manufacturer. This total weight includes the weight of your trailer or caravan, plus anything that is inside it. The weight of a van or trailer will usually be displayed on somewhere on it and will also be in the owner’s manual The ATM also includes the tow bar download, which is the proportion of the weight that is applied to the towbar. As a general rule, this will is about 10% of the trailer weight.


GCM – gross combined mass – is the maximum weight allowed for your vehicle and trailer combined, as specified by the tow vehicle’s manufacturer. The vehicle’s GVM and the trailer’s ATM will determine the GCM. It’s so important to know your CGM as this will determine whether it is safe for the vehicle to be towing the particular trailer. If you have determined the GCM and found that the vehicle should not be towing the trailer at the current weights, you would then risk voiding your insurance if you still choose to go ahead with the towing. Not to mention it is unsafe for you and other drivers.

How to weigh

The easiest way to measure these important weights is by using your nearest public weighbridge which you can find by a google search (try  Public weighbridges may be a traditional single deck with an operator on-site to assist you, or they might feature multiple decks and self-serve 24/7 kiosks with automated credit card payment.

Top Towing Tip!

Choose your caravan or camper trailer before you choose your vehicle. The last thing you want is to invest in a new 4WD only to find out it won’t be able to tow the caravan you have your heart set on. And make sure the tow bar you choose is designed specifically to suit your vehicle and your towing capacity requirements – tow bars are not something to skimp on!

Thanks to Phil Thornton from George Day Caravans and Motorhomes for these valuable towing tips. For more Tips and Tricks on 4WDriving, Caravanning, Camping, Fishing and Boating, visit

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