What car modifications are illegal in Australia?

If you like to personalise your car with accessories or modifications, the laws are more complex than they used to be. There are a few hoops to jump through to make sure your car is legal to drive on the road if you plan to modify it. Reading this guide could save you the hassle of a defect notice, an expensive fine, a denied insurance claim – or even a crash.

One reason that car mods have more strict regulations around them and are more complex is that modern vehicle safety features are far better and more nuanced themselves.

Regulators don’t want owners mucking around with their cars to the point that these safety features don’t work as they should. An example of this is electronic stability control (ESC); if a modified suspension is fitted, it could affect the operation of the ESC.

The other main concern held by the lawmakers to do with car modification regs is any subsequent increase in emissions – both noise and greenhouse gas emissions.

So, we’re laying out the broad sweep of what modifications can and cannot be done. But, as ever, seek clarification from an automotive engineer and/or your local registration authority before doing any such changes to your car.

Laws and their interpretation change over time, and there is also a mountain of mods we simply don’t have the space to cover off here.

The federal government is responsible for setting out the parameters for road vehicle compliance in Australia under the Australian Design Rules (ADRs). But the rules have changed since ADRs were introduced in 1970.

For example, a car built to suit the ADRs valid in 1975 doesn’t necessarily have to comply with all the extra ADR requirements of a car built in 2025.

There are also other, often less stringent compliance requirements in place for low-volume or personal use imports, but we are assuming you want to modify a car already here and registered.

Modifications ultimately come under state or territory regulations. The regulations require modified vehicles to be fit for use on roads and road-related areas by maintaining compliance with all applicable vehicle standards, including the relevant ADRs and to not increase the risk of injury to the vehicle’s occupants and other road users.

To make sure that there was consistency for technical standards across all jurisdictions, the National Code of Practice (NCOP) for Light Vehicle Construction and Modification (also known as Vehicle Standards Bulletin 14) was created in the early 2000s (and has been regularly updated since).

VSB 14 gives a national outline for light vehicle modifications, covering the minimum design, construction, installation and performance requirements, among other things. This is basically the document that anyone wanting to modify a road vehicle weighing less than 4.5 tonnes should look at first.

While VSB 14 covers off most modifications you can and can’t do in Australia’s states and territories, when it comes down to the finer administrative points of vehicle registration, obtaining exemptions, obtaining modification approvals, vehicle inspections, preparation and submission of reports and the payment of appropriate fees and charges, it is all up to the individual state or territory.

There are basic things that you can change on a car without having to seek approval, such as suspension, wheels, tyres and seats – but only up to a point.

While you might not need approval for a certain ‘mod’, any such change must not end up causing other safety-related problems.

For example, if you fit new wider wheels and tyres that meet all the measurement requirements laid out in VSB 14, but the wheels or tyres end up scraping on the body or suspension, then you could still end up with a defect notice.

Lowering suspension is allowed, so long as it is by no more than one third of the original suspension travel, the front and rear are both equally lowered and that minimum ground clearance requirements are met. An off-road vehicle can be raised by up to 50mm according to the document NCOP11 Section LS Suspension and Steering V2.1.

However, 4WD lifts are just one example where each jurisdiction makes its own rules. For separate-chassis 4x4s, you can do a suspension lift of up to 50mm and a tyre diameter increase of up to 25mm – so a total of 75mm – without certification in NSW. In the Northern Territory, it’s 100mm. In most other jurisdictions, it’s 50mm without an engineer’s certificate.

Sports shocks and sway bars for any vehicle is also okay, while retrofitting a factory power steering system (typically for older vehicles where power steering was a factory option) is also permitted.

All vehicles sold in Australia since 1972 have a tyre placard fitted, nominating tyre specifications for that vehicle. If your vehicle tyre size has become obsolete, you can buy replacements of another size without needing certification provided that the load rating is not less than for the original tyres, and that tyre speed rating is a minimum of ‘S’ (180km/h) where the original tyres had a higher rating.

Off-road tyres are a separate area. If you own a 4x4 – typically the ADR NC category, so we’re talking Toyota LandCruiser and the like, not soft-roaders such as the Toyota RAV4 – you can have tyres with a minimum speed rating of N (140km/h).

For any non-standard light-vehicle tyre replacement, they must be no more than 26mm smaller or 15mm larger in overall diameter than the original equipment tyres. For off-road passenger or goods vehicles, the tyres must not be more than 50 per cent wider than the originals.

Wheels can be replaced, so long as they don’t increase overall track width by more than 25mm for cars and 50mm for 4x4s (vehicles classified as MC, NA and NB under the ADRs).

An interesting requirement that might trip up some is when using wheels and tyres fitted to a manufacturer’s sports model on another variant. Under paragraph 4.2.7, VSB 14 says you must also change the suspension components, such as springs, shocks and sway bars.

A steering wheel can be replaced, but it must be marked as complying with ADR 10 (after 1970) or ADR 69 (after June 1995). For an ADR 69 vehicle, this concerns driver head protection in a frontal crash, which usually resulted in an airbag steering wheel being fitted at the factory.

So, if you want to put another steering wheel on, it must be either an identical airbag steering wheel or a factory option for that particular car. No replacement steering wheel should be less that 330mm in diameter and removable steering wheels are not allowed.

You can also replace seats in the vehicle, but only with those optional for the same make and model, and that are basically bolt-in (no modifications to the seat or seat base).

So, for example, if your car is a base model with manually adjustable cloth seats, you could fit the optional factory sports seats offered by the manufacturer to the Australian market.

Items like seat belts and other safety features can’t be downgraded because of the swap. If your vehicle had side airbags in the seats, the replacement seats must also have them and be compatible with the car’s existing airbag deployment system.

Aftermarket window tinting is also okay to do without getting certification, but you really need to check with your state or territory. Window tinting requirements are under the Australian Vehicle Standards Rules (AVSR), which apply to all vehicles no matter when they were built.

Law does state in VSB 14 that there has to be a minimum 70 per cent luminous transmittance for windows in front of the front seats (windscreen and front side windows) and minimum 35 per cent for those behind the front seats (except for Northern Territory only, where it is 15 per cent minimum at the rear).

Tinted strip is allowed on the windscreen, so long as it covers no more than 10 per cent of the windscreen upper area and does not enter the area of glass where the windscreen wipers sweep.

VSB 14 also says you need to have a mirror on both sides of the vehicle if you are applying tinted film, which might trip up owners of older cars which had just a driver’s side mirror fitted.

It is also illegal to have reflective window tint film (that is more than 10 per cent reflective), and bubbled or distorted window film that impairs visibility.

There are plenty of more extensive mods you can have done, but they will need a licensed certifier to inspect your modifications and then issue a compliance certificate, provided they are satisfied the modifications comply.

Depending on what you’re modifying, this certification can cost about $600 – or much more. It’s a good idea to keep a copy of any such approval in your car in case you are pulled over.

If you want to lift a 4x4 ute or off-road wagon between 50mm and 150mm (depending on the jurisdiction) you’ll need certification under LS codes. If you want to fit seats out of another production vehicle that had approved seats in it, you’ll need certification under the LK codes.

Under the sub-section titled ‘National Guidelines for the Installation of Electric Drives in Motor Vehicles’, VSB 14 also covers what may become in time a common conversion – an internal-combustion powertrain substituted with an EV one.

There are many requirements for ‘electro-modding’, such as safety markings for high voltage, safety for power disconnection, windscreen demisting capability and much more. The upshot of all this is it doesn’t assume even the simplest modification is straight-forward and street-legal.

Although the ability for enthusiasts to legally modify our vehicles is still alive and well, the legal restrictions make changing vehicles from their standard specs more complex than ever.

Some other more significant mods can be done, but they will need a certified engineer to approve and sign off on the modification.

Even what seems a minor modification to your car can end up being illegal and cost you a defect notice fine or even insurance claim denial.

Make sure you read the relevant parts of Vehicle Standards Bulletin 14 before attempting any mods.

The final word on modifications comes from your state or territory registering authority such as RMS or VicRoads – check with them before doing any changes.

You can change some items without certification such as window tinting, suspension, tyres, wheels and seats – but only up to a point.

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