How to Read a Trailer Spec Sheet

Every Australian trailer listing looks the same: a wall of twenty-odd bullet points. Hot dipped galvanised. Fully welded. 7-leaf eye-to-eye springs. Mechanical override disc brakes. 14″ Sunraysia rims. Two trailers a thousand dollars apart will have nearly identical lists, and nothing tells you which differences you'll feel in five years.

This guide decodes the list. For each spec: what it means, when it genuinely matters, and when it's there to fill a line.

Independent guide. We don't sell trailers and aren't affiliated with any manufacturer. Specifications vary between builders, so always confirm against the actual trailer and its compliance plate.

The specs that decide how long it lasts

Hot dipped galvanised vs painted

Hot dip galvanising means the finished steel is dunked in molten zinc, so the coating bonds to every surface: inside box sections, inside welds, into corners. Painted steel only protects what the brush reached.

When it matters: a lot, and especially near the coast or with boats. A painted trailer that lives outside in Queensland will show rust at the welds and chassis rails within a few years. Galvanised trailers look duller and slightly rough, which is normal and not a defect.

Watch for the wording. "Galvanised steel" can mean pre-galvanised sheet that was cut and welded afterwards, leaving raw steel at every cut and weld. "Hot dipped galvanised" (dipped after fabrication) is the one that protects the whole thing.

Fully welded vs bolted

A fully welded body and chassis has no bolts working loose and no gaps for water to sit in. Bolted construction is cheaper and easier to repair panel-by-panel, but the joints move over corrugations and eventually rattle and wear.

When it matters: moderately. For a trailer that mostly does dump runs, bolted is fine. For heavy or frequent loads on rough roads, welded holds together better.

Checker plate thickness

Usually quoted as 2.0 mm or 2.5 mm checker plate for floor, sides and gates. That half-millimetre is roughly a 25% increase in material, and it's the difference between a floor that dents under a dropped engine block and one that doesn't.

When it matters: if you load anything hard, sharp or heavy. For garden waste it's irrelevant.

The specs under the trailer

Leaf springs, or "7-leaf eye-to-eye"

Leaf springs are stacks of curved steel strips. Eye-to-eye means both ends have rolled eyes bolted to shackles (the common, well-supported arrangement), as opposed to slipper springs which sit loose at one end.

More leaves means a higher load rating and a firmer ride. But more is not automatically better: a heavily-sprung trailer running empty bounces hard, which is worse for the load and the trailer. What you want is a spring rated to match the trailer's ATM, not the biggest number available.

When it matters: as a rating check, not a bragging number. Compare the axle and spring rating against the ATM, not against the other trailer's leaf count.

Axle type

A solid round axle is a single bar through the hubs. Square axles are also common. What actually matters is the axle's load rating (e.g. 1,400 kg) and that it's at least the trailer's GTM.

Where you should pay attention is braked vs unbraked axles: retrofitting brakes to an unbraked axle is expensive, so if you might ever load past 750 kg, buy the braked axle up front.

Rims and tyres, or "14″ Sunraysia"

Sunraysia is a rim style (the multi-hole pattern), not a quality standard. The real questions are:

• Load rating of the tyres. "Light truck" (LT) tyres carry far more than passenger tyres and are what you want on a working trailer.
• Stud pattern, if you want the spare to match your car's. A genuinely useful convenience that no spec sheet flags.
• Rim diameter. Larger rims roll cooler and wear bearings less at highway speed.

When it matters: the tyre rating matters, the rim's name doesn't.

The specs that are about the law

Brake type

This is where a spec sheet directly meets the regulations:

Mechanical override brakes (also called surge brakes) work by the trailer pushing against the coupling as you slow. They're simple, need no wiring, and are common on trailers up to 2,000 kg, including boat trailers, since there's nothing electrical to submerge.

Electric brakes are controlled from a brake controller in the tow vehicle. Above 2,000 kg you need a breakaway system, and electric brakes are the practical way to get one.

So "mechanical override disc brakes" is a perfectly good spec on a 1,400 kg trailer, and a dead end if you're planning to grow into a 2,500 kg one. Our brake requirements guide covers the thresholds properly.

Disc vs drum: discs shed heat and water better (again, good for boats); drums are cheaper and better sealed against dust. Both are legal.

Coupling rating

The coupling is stamped with a rating in kg (commonly 2,000 kg) and a ball size (50 mm is the Australian standard). The coupling rating must be at least the trailer's ATM. Note that the coupling on the trailer is the socket, the ball is on your car.

Safety chains and shackles

Rated chain and load-rated shackles are legally required, and the rating must suit the ATM. Trailers over 2,500 kg ATM need two chains. This is one spec worth checking is actually rated rather than a hardware-store shackle.

Plug type, or "flat 7-pin"

The connector between car and trailer. Flat 7-pin is the most common Australian standard; round 7-pin and 12-pin also exist. It's not a quality issue, but a mismatch with your car means buying an adapter, so check before you buy.

ADR compliance and the compliance plate

ADR (Australian Design Rules) compliance is not optional, because a trailer must comply to be registered. Its presence on a spec sheet is reassurance, not a differentiator. What you actually want is the compliance plate on the trailer showing VIN, ATM, GTM and tare. Those numbers, not the brochure, are what the law goes by.

Manufacturer or industry accreditations beyond ADR are quality signals, not legal requirements.

The specs that are really convenience

None of these affect durability or legality, but they change daily use:

• Extended draw bar: a longer A-frame is more stable to tow and much easier to reverse. Genuinely useful.
• Jockey wheel: often listed as "free". Assume every trailer has one; it's a $60 part.
• Tie-down rails: more anchor points make restraining a load easier and safer. Worth having.
• Full-length side steps: handy for reaching over the sides, and they protect the panels.
• Removable / fold-down gates: front and rear gates that drop make loading long items far easier.
• Tilt function: good for loading mowers and bikes; adds cost and moving parts you may never use.
• LED lights: brighter, tougher and last longer than incandescent. Standard on most new trailers now.

How to compare two trailers in five minutes

1. Compliance plate first. ATM, GTM and tare. Payload = ATM − tare. If the payload doesn't cover your load, nothing else matters.
2. Check it against your car. Towing capacity, tow ball limit and GCM. See what size trailer you need.
3. Galvanising: hot dipped after fabrication, or just pre-galvanised sheet?
4. Brakes: does the type suit the ATM you'll actually load to, now and later?
5. Ratings, not adjectives: axle rating, tyre rating, coupling rating, chain rating, all at or above the ATM.
6. Everything else is comfort and preference. Price the extras separately; a cage is typically $260–$360 and a canvas cover $490–$590, so a "cheaper" trailer with the extras added can end up dearer.

Quick FAQ

What does "fully welded" mean on a trailer? The body and chassis are welded rather than bolted together, so no joints work loose and no gaps hold water, but harder to repair panel-by-panel.

Is hot dipped galvanised worth it? In Queensland, yes, especially coastal, and essential for boat trailers. It protects inside sections and welds where paint never reaches.

Are more leaf springs better? No. More leaves means a higher load rating and a firmer, bouncier ride when empty. Match the spring rating to the trailer's ATM instead of chasing the count.

What are override brakes? Mechanical brakes applied by the trailer pushing against the coupling as you slow. No wiring, common up to 2,000 kg ATM and popular on boat trailers. Above 2,000 kg you need all-wheel brakes plus a breakaway system.

Does ADR compliant mean it's a good trailer? No. It means it's legal enough to register. Every registrable trailer must comply. Judge quality on galvanising, construction and component ratings.

Check the numbers, not the adjectives. Put the plate figures into the Compliance Auditor to see the ATM, braking and tow ball requirements for your load, or use the Size Recommender to work out the size and rating you should be shopping for, with no sign‑up.

Independent reference only. Specifications vary between manufacturers; confirm against the actual trailer and its compliance plate, and verify with TMR or a certified RPEQ engineer before purchasing, building or registering a trailer.