DO I NEED A COF AND LT400 CERTIFICATE FOR MY TOWBAR ?

Suppose you want to have a towbar fitted to your heavy vehicle, passenger vehicle or motorhome in New Zealand, and your vehicle is on a Certificate of Fitness (CoF). In that case, you will likely need an LT400 certificate. We’ll walk you through what’s required, step by step.

What’s a Certificate of Fitness (CoF) — and Do You Actually Need One?

If you drive a motorhome, truck, or commercial vehicle or passenger service vehicle, you will be required to have a COF. It stands for Certificate of Fitness, and it’s basically a regular safety check to make sure your vehicle is roadworthy — especially when it’s doing the long haul.

So who needs a CoF?

• If your vehicle is over 3,500 kg GVM (gross vehicle mass), it’s a must.

• If you’re running a shuttle, bus, taxi, or rental, even lighter ones, it’s likely required too.

There are two types of CoF:

1. CoF A – for light vehicles under 3,500 kg GVM, like taxis, small rental cars or Ubers.

2. CoF B – for the bigger vehicles: trucks, motorhomes, large vans — anything over 3,500 kg GVM.

If you’re unsure which applies to you, we can help you determine the correct option.

Towbar Requirements for CoF A vs CoF B

CoF A vehicles need towbars with a low volume cert plate that indicates:

• Make and model

• Towing capacity

• Towbar code

• Build number

• Vertical Load

CoF B vehicles require an LT400 certificate, issued on-site by an independent, NZTA-approved heavy vehicle certifier, once the installation meets the standards.

What Is an LT400 Certificate?

LT400 Certificate Sample

If your vehicle falls under the CoF B category (that’s anything over 3,500 kg GVM), you’ll need something called an LT400 certificate. This isn't just a form, it’s proof that your towbar has been designed, installed, and signed off by a qualified heavy vehicle certifier to meet strict New Zealand standards (NZS 5446).

Once issued, a copy of the certificate gets uploaded into the NZTA system, and you’ll also receive a compliance plate. This rating plate must be attached to your vehicle near or on the towbar.

The LT400 is, however, designed to be used separately, so make sure to keep it (like in the glovebox). It may be requested by the testing station when you go for your COF.

GVM, Why Combined Mass Is a Big Deal

When it comes to towing with a motorhome or camper, weight matters — a lot more than many people realise.

Let’s break it down:

• GVM (Gross Vehicle Mass) is the maximum your vehicle can weigh when its fully loaded, this includes passengers, gear, water tanks, and so on.

• GCM (Gross Combined Mass) is the total allowable weight of your vehicle and whatever you’re towing.

Many owners mistakenly assume that if their motorhome can legally tow 2,000kg, they can hook up a trailer without issue. But if your GVM is 4,000kg and your GCM is only 5,200kg, your trailer must not exceed 1,200kg — not the assumed 2,000kg.

The certifying engineer will determine the maximum towing capacity, which will include factors such as the strength of the chassis, design of the towbar and determination of the vertical load.

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TIP: Always check the GCM before buying or towing with a camper.

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How your Tow Rating is Determined

Although we provide you with an initial consultation and quotation, below are the technical and legal factors that the certifying engineer will use to determine the final tow rating:

1. Vehicle GVM & GCM Ratings

• GVM (Gross Vehicle Mass): Max legal weight of the vehicle fully loaded.

• GCM (Gross Combined Mass): Max combined weight of the vehicle and whatever it's towing.

2. Chassis Type & Construction

• Is it a ladder chassis, monocoque (unibody), or extended?

• Chassis extensions may lower capacity.

• Does the chassis go all the way to the rear? If not, additional reinforcement may be required.

Engineers may request photos or physical inspection of rear chassis rails, mounts, and crossmembers.

3. Mounting Points & Load Distribution

• Are the towbar mounting points strong enough?

• Are they correctly braced or reinforced to spread the load?

• Are factory points used, or has a custom bracket been welded/fabricated?

4. Material Strength & Towbar Design

• Grade and thickness of steel used in the towbar.

• Welding quality and fabrication method.

• Bolt types, torque specs, gusseting, and cross-member support.

Engineers may require FEA (finite element analysis) or load calculations for custom setups.

5. Vertical (Tongue) Load Rating

• Also known as downforce or static load.

• This is typically 10% of the braked towing capacity, but varies depending on design.

• Important for things like bike racks or A-frame towing (e.g. Suzuki Jimny on a camper).

6. Clearance & Obstruction

• Engineers will assess whether tanks, pipes, spare wheels, steps, etc., obstruct towbar mounting or create weak points.

“Obstructions like septic or water tanks often reduce viable mounting areas or limit reinforcement.”

7. Compliance with Standards

Engineers will ensure the design and installation comply with:

• NZS 5446 – trailers and towing hardware

• NZTA Heavy Vehicle VIRM – construction standards

• AS/NZS 4968 series – drawbars and couplings

• Manufacturer recommendations (where available)

8. Vehicle Use Case

• Is the vehicle used privately or commercially?

• Will it be towing regularly or occasionally?

• Is it fitted with brake controllers or electronic stability systems?

9. Inspection & Testing

• The engineer may require a physical inspection or a weighbridge certificate.

• In some cases, destructive or non-destructive testing may be used (for non-OEM towbar installs).

10. Labelling and Documentation

• Certifier ensures the final installed towbar has:

  • Make/model of vehicle

  • Towing capacity

  • Build number

  • Towbar code or ID

• This is often laser-etched or permanently labelled on the towbar itself.

Keeping Your LT400 Certificate Safe

Once your towbar has been certified and your LT400 certificate is issued, it’s not just a formality — it’s a legal document you’ll need to present:

• ✅ A copy is loaded into the Waka Kotahi (NZTA) system by the certifier

• ✅ A physical copy should always be kept in your glovebox

• ✅ It’s required to be shown at your CoF B inspection or if requested by an enforcement officer

You will receive a compliance plate, which is either:

• Affixed to your vehicle near the towbar, or

• Handed to you to store securely if affixing isn’t possible

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TIP: If you're buying a second-hand vehicle that is on a CoF and has a towbar fitted, check that it comes with a valid LT400 for the towbar — and confirm it's in the NZTA system.

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How Loadmaster Can Help

How our process works:

1. Consultation and Inspection - We discuss your towing requirements and inspect your vehicle

2. Towbar Design & Engineering — We account for GVM, GCM, chassis design, and potential obstructions (e.g. water tanks or septic).

3. Fabrication & Fitting - After designing the towbar, we will fabricate it to the standard (NZS 5446) at our facility in Christchurch.

4. On-Site LT400 Certification — We partner with NZTA-approved certifiers to certify your towbar installation, who will issue an LT400 certificate. (We keep a copy on file just in case)

5. Compliance Plate & Certificate — You’ll receive your compliance certification and plate or have it attached immediately — giving you full traceable certification. The certifying engineer will load this to the NZTA, and you will be fully compliant :)

Final Word

Whether your tow vehicle is a camper, bus, or truck, having the right certification protects you, your vehicle, and ensures you're compliant with NZ law. With Loadmaster, you're supported at every step, from design, through to certification.

Need help? get a quote visit our Quote Page or have a question we would love to help, pop into see us or enquiry though on our Contact Us page or phone 03 3415623.

We are located at 3 Racecourse Road, Sockburn, Christchurch.