How to read weight figures and examples
- Ratings are maximum limits, not measurements of your loaded setup. Confirm the exact variant and approved ratings.
- Measure loaded coupling weight. A percentage or the difference between ATM and GTM ratings does not establish today's coupling weight.
- An added load changes both axle reactions according to its position. A change is not a total axle load; use measured starting axle weights and add each load once.
- Combination mass is unhitched loaded vehicle plus total loaded trailer, or the sum of all coupled axle readings. Count coupling mass once.
- Examples and AI suggestions are planning aids, not verified measurements or compliance clearance. Unknown figures require measurement; active weight-distribution hitches and gooseneck arrangements need their own assessment.
Introduction
Just as vehicles have GVM, GCM and payload, caravans and trailers have their own weight terminology. The three figures that matter are:
These figures are shown on the trailer's compliance plate and registration documents. Understanding them is essential before matching a caravan or trailer to a tow vehicle.
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What Is Tare Weight
Tare weight is the empty weight of the caravan or trailer — with standard equipment, no occupants, no gear, no water tanks filled. It is the lightest the trailer can be.
**Where to find it:** Compliance plate on the trailer, or the manufacturer's specification sheet.
**Why it matters:** Tare weight is the baseline for calculating payload. A caravan with a tare of 1,950kg and an ATM of 2,200kg has a payload of 250kg — that is the gear, water tanks, gas bottles and occupants the trailer can carry before reaching ATM.
Illustrative Example
A Jayco Expanda caravan with tare weight of 1,950kg and ATM of 2,200kg:
For many caravans, the payload is modest. Filling water tanks alone can consume 60kg — nearly a quarter of the payload. This is why many owners travel with water tanks partially full rather than brimming.
> **Safety caveat:** Tare weight assumes standard equipment and no additions. If you add gear, water tanks or accessories to the trailer after purchase, the loaded weight will be higher. Weigh the trailer at a certified weighbridge to confirm its actual loaded weight.
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What Is ATM (Aggregate Trailer Mass)
ATM is the maximum legal loaded weight of the caravan or trailer — the weight the trailer is allowed to be at at its most loaded condition. It is shown on the compliance plate and registration documents.
The formula is:
ATM = Tare weight + Payload
ATM governs:
1. **Tow ball mass** — obtain the actual loaded coupling measurement. Do not calculate it from an ATM percentage.
2. **GCM** — compare the actual combined mass, counting coupling load once, with the GCM rating. Rated ATM is not an actual axle measurement.
3. **Tow rating** — the vehicle's tow rating must be at least as high as the trailer's ATM.
Illustrative Example
A vehicle with tow rating of 3,500kg and GCM of 6,900kg. A caravan with ATM of 2,200kg:
The caravan is within the tow rating and GCM. But if the same vehicle towing a caravan with ATM of 3,600kg:
> **Safety caveat:** ATM is a legal maximum. Your actual loaded trailer weight may be lower than ATM. For GCM calculations, use the actual loaded weight if you know it — but for actual towing checks, confirm the intended loaded trailer mass, the applicable vehicle and equipment ratings, manufacturer conditions and jurisdiction requirements. Comparing rated ATM with tow rating is a maximum-load scenario.
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What Is GTM (Gross Trailer Mass)
GTM is the permitted maximum mass supported by the trailer tyres when coupled. It is a trailer rating, not a load imposed on the tow vehicle rear axle.
Measure the actual trailer axle-group mass and compare it with GTM and the applicable trailer axle, tyre and suspension ratings. Measure the tow vehicle front and rear axle masses separately and compare each with its own rating.
Actual loaded trailer total mass equals actual coupling load plus actual trailer axle mass for the same loading condition without weight-distribution-hitch redistribution. Do not calculate actual coupling load by subtracting two maximum ratings.
Fictional example
A trailer total mass of 2,800 kg and a measured coupling load of 280 kg give a 2,520 kg trailer axle-group mass. Compare 2,520 kg with the trailer ratings. Vehicle rear axle load still requires its own measurement or a model with measured baseline and geometry.
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How These Three Figures Interact
The three trailer weight figures operate together:
1. **Tow rating check:** Compare actual loaded trailer mass with the applicable vehicle and equipment limits; rated ATM is a maximum-load comparison.
2. **GCM check:** Compare actual coupled vehicle axle masses plus actual trailer axle masses with GCM, counting coupling load once.
3. **Axle load check:** Compare each actual vehicle axle mass with its own rating, and actual trailer axle mass with the trailer GTM and axle ratings.
4. **Payload check:** Include actual loaded coupling download once in the vehicle mass tally.
The binding constraint is often the axle load check — many vehicle and trailer combinations pass the tow rating and GCM checks but fail the axle load check.
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Where to Find Trailer Weight Figures
If you cannot find any of these, the caravan may not be registered or may not have a compliance plate. Measurement with appropriate scales can establish actual mass, but cannot establish permitted ratings or registration status. Obtain the manufacturer's records and advice from the relevant authority or qualified certifier before relying on the trailer's limits.
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Sources and Review Method
The trailer weight terminology in this guide follows:
ClearPath uses manufacturer-published trailer specifications where available. Vehicle owners should always verify weight figures against their own compliance plate and registration documents.
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What Next
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