GVM, tare and trailer brakes explained

8×5 Tradesman Trailer/ 1990 Kg GVM/ 1 Piece design/ Compressor Box — tap to view8×5 Tradesman Trailer/ 1990 Kg GVM/ 1 Piece design — tap to view

Tare, GVM and payload

Tare is what the trailer weighs empty. GVM — gross vehicle mass — is the most it may weigh fully loaded, including its own weight. Payload is simply GVM minus tare: the actual weight of goods you can legally put on it. People routinely assume a trailer rated at 2,000 kg carries 2,000 kg of load. It does not. Subtract the tare first, and the real number is often several hundred kilograms lower than expected.

Your vehicle is usually the limit

The trailer rating is only half the equation. Your tow vehicle has its own towing capacity, often quoted as braked and unbraked figures, plus a maximum towball download and a gross combination mass covering vehicle and trailer together. The lowest of those numbers is your real limit. Check the vehicle handbook or compliance plate against the loaded GVM you actually intend to use — not the empty weight.

The brake thresholds

As a general guide under the Australian design rules: trailers up to 750 kg do not require brakes; between 750 kg and 2,000 kg require brakes on at least one axle; and above 2,000 kg require brakes on every wheel plus a breakaway system that applies the brakes automatically if the trailer separates. These are the national thresholds, and specific requirements should be confirmed with your state road authority.

Why the thresholds matter when choosing

The brake thresholds often decide the trailer, not the capacity. A trailer just under 750 kg GVM is simpler, cheaper and towable by more vehicles. Stepping above 2,000 kg brings electric brakes on all wheels, a breakaway system and usually a brake controller fitted in the tow vehicle. Work out what you genuinely need to carry before paying for capacity that brings obligations with it.

Towball download and loading

Roughly ten percent of the loaded trailer weight should sit on the towball — too little and the trailer sways dangerously at speed, too much and it unloads the tow vehicle front axle and spoils the steering. Load heavy items over or slightly forward of the axle, keep the load low, and restrain everything properly. How you load the trailer affects stability more than almost anything else.

Single or tandem axle

Single-axle trailers are lighter, cheaper, easier to manoeuvre by hand and simpler to maintain. Tandem axles carry more weight, ride more smoothly, and are considerably more stable at highway speed with a heavy load — and they keep going if a tyre fails. For light domestic use a single axle is usually right; for heavy or regular highway towing, tandem.

Registration and compliance

Trailer registration goes through your state road authority and the requirements vary by state and by trailer. We can talk you through the paperwork for the trailer you buy. Keep the compliance documentation with your records, and check tyre ratings and load restraint before the first trip rather than after.