Towing terminology explained

[HK1837]

This should be simple and easy to follow, but it ain't!

I'll try, learned some today.

Trailer terms:

ATM
GTM
GCM.

ATM is Aggregate Trailer Mass. Basically the trailer maximum weight (trailer plus load) when sitting on a weigbridge on its tyres and jockey wheel.

GTM. Gross Trailer Mass. As above except trailer attached to the towing vehicle, and only the trailer's tyres sitting on a weighbridge. Will be less than the ATM by the weight on the towball of the towing vehicle.

GCM - Gross Combined Mass. Weight of both tow vehicle and trailer on a weighbridge.

Now, most State based authorities (RTA/RMS in NSW) say that you don't need brakes up to 750kg GTM, then brakes on one axle up to 2000kg GTM. Over 2000kg GTM you have brakes on all axles and an automatic breakaway system. Over 2500kg ATM you need twin chains.

Now almost all manufacturer's specify unbraked trailer towing up to 750kg, which one would assume is 750kg GTM as that is the rule in most/all States. Therefore the maximum towing capacity (eg my Hilux is 2250kg and a Falcon ute is 2300kg) would also make sense to be GTM. BUT it ain't, it looks like the 750kg unbraked is ATM and also the maximum is also ATM. So your unbraked trailer is now something like 690kg GTM plus 60kg on the towball. And the Falcon is about 2100kg GTM maximum plus 200kg on the towball.

So this makes it very important that you be careful when towing. Both my trailers show GTM and TARE on the compliance plate, not ATM. It would appear manufacturer's are not following registry authority or trailer manufacturer convention when specifying limits. Problem will come with a van for example stating 2300kg GTM, and you think this is OK behind your Falcon ute with correct 2300kg towing equipment. The van is really 2530kg as it puts 230kg on the towball, but the Ford is only allowed to tow 2300kg ATM.