Understanding ATM, GTM and Tare Weight — What Every Caravan Buyer Needs to Know

If you've been looking at caravans for more than five minutes, you've already seen terms like ATM, GTM, and Tare weight. They look technical, but they're actually straightforward — and getting them right could be the difference between a safe trip and a dangerous one.

Why These Numbers Matter

Towing a caravan isn't like towing a trailer full of soil. A caravan is a large, heavy, aerodynamic object that puts real mechanical demands on your tow vehicle. Exceed your legal limits and you risk damage to your car, a fine from the police, and — most importantly — a loss of control on the road.

The good news: once you understand what these three numbers mean, you can quickly work out whether any given caravan is a match for your car.

Tare Weight: What the Van Weighs Empty

Tare weight is the weight of the caravan as it leaves the factory — with no water in the tanks, no clothes, no food, no gas, no camping gear. Think of it as the "empty" weight.

Why does it matter? Because it's the starting point for everything else. A van with a tare weight of 1,800 kg will always be at least 1,800 kg, no matter what. Probably 2-5% more if you add some extras .

When you load up for a trip — filling the water tanks, packing your wardrobe, adding bikes, tools, food for a fortnight — you could easily add another 300–400 kg. That's why tare is just the beginning of the weight conversation, not the end of it.

Typical tare weights:

• Lightweight pop-top: 900–1,200 kg

• Standard caravan: 1,400–1,900 kg

• Large family van: 1,800–2,500 kg

• Off-road caravan: 2,200–3,000 kg

ATM: The Maximum Your Van Can Legally Weigh

ATM stands for Aggregate Trailer Mass. It is the maximum legal weight of the caravan when fully loaded — including water, gas, food, clothes, and everything else you plan to take.

The ATM is set by the manufacturer and is stamped on a compliance plate attached to the caravan (usually near the drawbar). It is a legal limit, not a suggestion. You must not exceed it.

Here's the important connection: your tow vehicle must have a towing capacity that is equal to or greater than the caravan's ATM.

So if your caravan has an ATM of 2,500 kg, your car must be rated to tow at least 2,500 kg. If your car is only rated to 2,000 kg, that caravan is not legally towable with your vehicle — regardless of how it feels on the road or its tare weight.

Where to find your car's towing capacity:

• Owner's manual (look for "maximum braked towing capacity")

• Manufacturer's website (search your make, model, and year)

• The vehicle's compliance plate

GTM: A More Technical Number for the Same Purpose

GTM stands for Gross Trailer Mass. It is similar to ATM but slightly more technical — it is the maximum load that can be placed on the caravan's wheels when it is being towed (i.e. the loaded weight minus the load on the towball).

In most practical situations you'll use ATM rather than GTM when shopping for a caravan. GTM becomes relevant when you're checking your car's towball download capacity — but for everyday buying decisions, ATM is the number to focus on.

The simple rule: ATM > GTM always. If you ever see a listing where GTM equals or exceeds ATM, that's a data entry error — query it with the seller.

Towball Download: The One Extra Number to Know

While you've got the compliance plate in view, check one more figure: towball download (sometimes called "ball weight" or "nose weight").

This is the downward force the front of the caravan exerts on the towball of your car. It matters because:

1. Your car has a maximum towball download limit (typically 200–350 kg for most 4wd vehicles)

2. Too much nose weight can compress your car's rear suspension and affect steering

3. Too little nose weight can make the caravan unstable and prone to sway

A general rule of thumb is that ball weight should be 7–15% of the loaded caravan weight. If your loaded van weighs 2,000 kg, you want approximately 140–240 kg on the towball.

What Happens if You're Over the Limits?

This is where it gets serious. In Australia, towing above your vehicle's rated capacity:

• Voids your insurance. If you're in an accident and investigators find you were over your rated limits, your insurer can refuse to pay — for damage to your car, the caravan, other vehicles, and third-party injury claims.

• Is a traffic offence. Police can weigh your rig at any time. Fines vary by state but can be substantial, and you may be required to unload the van on the spot.

• Is genuinely dangerous. An overloaded combination is harder to brake, more prone to sway, and more likely to jackknife in an emergency.

How to Check Your Actual Loaded Weight

If you're serious about caravan safety, visit a public weighbridge before your first trip — most service stations and transport depots have them, and they charge a few dollars. Weigh the complete rig loaded as you'd actually travel.

Many experienced caravanners do this annually. It's the only way to know for certain what you're actually towing.

Decoding a Caravan Listing

On VANTURE, you'll see ATM and Tare weight listed in the specs panel of most listings. Here's how to read them quickly:

Example listing:

• Tare weight: 1,650 kg

• ATM: 2,200 kg

• Available payload: 550 kg (ATM minus Tare)

That 550 kg is your budget for water (1 litre = 1 kg), food, clothes, accessories, and passengers' belongings (average 70kg per person). For most couples doing a two-week trip, that's comfortable. For a family of five, it gets tight fast.

Before you enquire on a listing, check whether the ATM is within your vehicle's towing capacity. It takes 30 seconds and could save you a very expensive mistake.

Browse caravans with full weight specs on VANTURE →

Quick Reference: Weight Terms at a Glance

Term What it means and What to check it against:
Tare weight Empty van, factory spec Starting point for payload calculation
ATM Maximum legal loaded weight Must not exceed your car's towing capacity
GTM Max load on van wheels when towing Relevant for towball download calculations
Towball download ball weight on your car's towball Must not exceed your car's towball limit
Payload ATM minus Tare How much you can actually pack

If you're unsure whether a particular caravan suits your vehicle, talk to a licensed caravan dealer or your motoring club before you buy. Getting the weights right isn't just a legal box to tick — it's what keeps you and everyone else on the road safe.