Towing terminology explained

**HK1837** · 07-05-2014, 07:10 PM

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.

**Taily** · 07-05-2014, 07:40 PM

All of that and nothing from the towbar manufacturers about how much load you can carry on the tow vehicle at the same time (GCM)? No wonder Joe Public is are confused when they think they can chuck a tonne on the back of a ute and another tonne in a trailer behind - "Coz I can tow up to 1600kg"...

**Big Rob** · 08-05-2014, 02:12 AM

Yeah, it is extremely confusing. I was of the opinion that the weight of the loaded trailer couldn't exceed the weight of the towing vehicle.

eg, A Holden van towing a car trailer could only tow a car that weighed a lot less than the van. I have seen vans towing other vans, which doesn't seem right, and down my way every tourist has a boat and there's some BIG ones that are being towed by all sorts of cars that seem inadequate. I don't know how they make it back up the boat ramp (or the trip here from Canberra).

**HK1837** · 08-05-2014, 07:39 AM

It now goes by what the manufacturer states. What I don't get is a Falcon ute (1815kg Kerb) and a my Hilux (just under 2000kg) can both tow 2300kg. Yet a Ranger xtra cab 4x2 (1700kg) can tow 3500kg.

**Dick61** · 08-05-2014, 01:00 PM

Why on earth did you start this post Byron? I read all the info in the first installment and now my brain hurts!

**HK1837** · 08-05-2014, 01:56 PM

I see it that if me (a degree and trade trained technical person who is a nut for technical stuff) was confused and wrong about maximum towing limits for vehicles, that others here are probably also not aware of the possible pitfalls. So if I can try to help educate a few people here I might save them from future grief!

**ambientgoat** · 08-05-2014, 02:08 PM

All I got was, since I have a ranger I should go and buy lots of wrecks and trailer them home. The girl is going to be thrilled!

**playwme** · 08-05-2014, 02:17 PM

Tis good info Byron. Not that relevant to me most of the time as my tow vehicle weighs close to 4 tonne empty, but it could make the difference for someone else.

**HK1837** · 08-05-2014, 05:36 PM

I talked to someone at work today who has a 2500kg plated caravan, and thought he was fine towing behind a 2014 Hilux (2500kg towing capacity). He wasn't aware he was exceeding the manufacturer's limit by about 250kg as the van on it's own not coupled to the tow vehicle is about 2750kg.

**Big Rob** · 09-05-2014, 02:59 AM

Yeah, this is confusing to say the least.

Many drivers are towing way too heavy loads thinking they are OK. Most of the time they are, but in a desperate situation they may be in trouble.

And how do the cops work it out?

And how would insurance companies deal with it in the case of an accident?