We all know that when owning a car, we all want to add a personalised touch. For some it’s simply adding seat covers, some fluffy dice and an air freshener, for others it’s a little more involved, be it adding aftermarket wheels and a body kit, to souping up the performance of the engine. When carrying it modifications however, it’s important to understand the rules and regulations that govern what you can and can’t do to your car. By making sure your vehicle complies with your local rules and regulations, it will save your time, hip pocket and in some cases, a court hearing, from defect notices.

It is important to know that these are only summaries on the legalities, and in most only applies specifically to cars. There are differences in laws between cars (or car derivatives), off-road passenger vehicles, or commercial vehicles.


Aftermarket Wheels
Maximum wheel size – Rolling diameter cannot increase more than 15+mm/-26mm.

It’s no secret that most car manufacturers look for functionality and low cost when they put wheels on cars. They’re designed to go round and round, and not add style, so the most common modification performed is adding aftermarket wheels. With such a huge variety of wheels available, it’s important that the rim and tyre choice you make is the correct one.

Now to make sure you make the legal choice of rim and tyre combination, you need to know the stock combination. If your car still has standard wheels fitted, you can simply look at the tyre and find the size written on. If not, your car should have a tyre placard fitted, this is usually on the inside of the driver’s door, or inside the glove box. You’re looking for a number combination of ###/##/##, for example, 195/60/R14.

To continue further, you need an understanding of what the numbers and letter mean. As a brief summary;

• 14 denotes the rim diameter measured using the imperial system (i.e. 14”).
• 195 is the section width. It indicates the width of the tyre at it’s widest point in millimetres (mm)
• 60 is the aspect ratio. It indicates the profile (or tyre wall height) as a percentage of the width, so 60% of 195 equals a tyre wall height of 117mm.
• R stands for radial construction. It’s not of much importance as most tyres are constructed this way.
• V is the speed rating of the tyre. Different types of tyres have different speed ratings (maximum speed they can safely support).

The final figure you need to know is the overall rolling diameter. This can be calculated using the following;
RD = 2 x (60% of 195) + 14” x 25.4mm
RD = 234 + 355.6
RD = 589.6mm

For more specific information you can visit http://www.carbibles.com/tyre_bible.html

So now we know what everything means, we can look at the legalities.
To start with, contrary to common belief, there is NO such thing as the 2” rule (i.e. Cannot have rims more than 2” over stock size).

Changes in rolling diameter actually have an adverse affect on your speedometer. Increase the RD, and your speedo reads higher than you’re actually travelling. Decrease the RD, and your speedo reads lower than you’re actually travelling. This means you can be speeding without knowing it, and you’ll have to wear the fine if you get caught.

A decent tyre calculator (http://www.alloywheels.com/tyrecalc.asp) can help you figure out the best tyre size. A tyre shop should also have a book that gives options for tyre sizes and can assist you in making the right choice.

It is also important to note several other restrictions regarding wheels. Firstly, each axle must be fitted with the same tyre and wheel size, including rolling diameter, width and offset. Secondly, you cannot increase wheel width by more than 1.3 times the manufacturer’s widest optional tyre. Thirdly, tyres must have a minimum tread depth of 1.5mm on any part of the tyre that touches the ground, although it’s recommended to replace tyres prior to reaching this depth.  For tyres, they must meet or exceed the load rating listed on the tyre placard, as should the speed rating.

Note that it is ILLEGAL to replace light truck tyres fitted by the manufacturer with a passenger tyre (unless the tyre placard states otherwise). Passenger tyres do not have the correct load rating capacities to meet the loads the vehicle can carry as stated by the manufacturer. This includes most 2WD utilities/utes.


Lowering
Legal Minimum Height – 100mm

Following new wheels, many people move onto lowering their vehicle height. It is important to know that a vehicle must be at least 100mm of the ground, measured from the lowest point on the vehicle (usually the exhaust or a body kit). It’s important to know that this figure should be measured when the vehicle is fully loaded. That means with passengers, luggage and a full tank of fuel. Therefore it’s not recommended to attempt to get your vehicle height as close to 100mm as possible, because as soon as you load up your friends, you’re likely to drop below that limit. Further, you cannot remove or reduce more than one third (1/3) of the working travel of the suspension from its original height.


Exhausts
Maximum dB limit – 90db (or 96dB pre-1982)

Changing the exhaust on a vehicle is also popular. However there are technicalities that can make legality an issue. Generally, the decibel level of an exhaust cannot be more than 90db measured 5m from the exhaust at a 45 degree angle on deceleration from a particular RPM. For vehicles manufactured before 1982, the maximum decibel level is 96db. This is where the technicalities start; altering the exhaust is classed as modifying a silencing device from manufacturer specifications. It is possible to be defected simply for this, even if you are under the limit. However, a sound level test is all that’s required to certify that your altered exhaust still complies with the specifications by proving it still reads under the limit. Aside from noise levels, exhausts must also comply with emissions standards. If a car is manufactured after February 1986, it must have a catalytic converter fitted. This also applies to vehicles with an engine manufactured after this date. Failure to have a cat fitted can result in a hefty fine from the EPA.


Pod Filters
Properly secured and attached to the car body.

Another common modification is the removal of stock air box from a car’s air intake and replacing it with a pod filter. There’s lots of misconception regarding the legalities of pod filters. It is legal to replace an air box and panel filter provided the filter is properly attached. This means a proper stainless steel clamp (not zip ties) and a metal piece connecting the filter to the body of the car. It should be noted that in NSW, it’s a requirement for pod filters to be completely enclosed in a box as well as properly secured. However it’s recommended to enclose or shield the filter from the engine bay anyway to prevent the intake sucking in hot engine air.


Steering Wheels
Not smaller than 330mm

It’s no secret that after several years, factory steering wheels can get quite worn and dated, and replacing them with new sportier versions is common. However, once again, certain limitations apply. A steering wheel cannot be reduced by more than 25mm from the factory steering wheel size but must not be less than 350mm*. If a steering wheel is fitted with an airbag, it cannot be replaced or removed with an aftermarket steering wheel. Finally, every car must have a working horn, so having a horn button is also a requirement.


Lighting

Adding extra lights or neon’s can bring more attention to your car, but it’s not always wanted. The fitting of under body lights (neon’s or LEDs) or other lights is legal, provided they meet several criteria. For under body lights, they cannot be distracting to other driver’s, this means you cannot see the source of the light. Flashing lights (excluding indicators) are illegal except for emergency vehicles or special vehicles in hazardous situations (usually amber lights on construction vehicles or tow trucks etc).

Colours are also limited. Blue lights cannot be fitted to any vehicle at any time, unless it an emergency vehicle – this includes under body lights, LED washers or parkers. White lights can only be visible from the front of the vehicle; red lights can only be visible from the rear of the vehicle. Purple cannot be used due to their use by the Department of Transport. Yellow (or amber) should only be used as clearance markers.


Complex Modifications

There are some modifications that require specific approval by engineers or ‘Approved Persons’ and the fitting of a modification plate (or blue plate in Queensland). These can include the fitting of aftermarket seats, particular engine conversions, turbocharging or supercharging, brake conversions, major suspension changes, the list goes on.

A full list of the different modification codes and can be viewed here - http://www.roadsmart.com.au/docs/NCOPApprovalCodes.pdf

The National Code of Practice for Light Vehicle Construction and Modification has been put in place to create uniform standards through Australia and has been tentatively adopted by each State and Territory. Each NCOP document has information highlighting specifications and requirements for modification approval. However, before considering making any complex modifications, it is important to consult an engineer or Approved Person first to confirm the requirements and specific legalities of each State, as due to the voluntary adoption, there are still minor differences between jurisdictions. For full specifications, visit http://www.infrastructure.gov.au/roads/safety/bulletin/vsb_ncop.aspx


Disclaimer

This document should only be used as a guide and cannot be used as a legal document in a court of law. It should not be treated as any form of legal advice.
Prior to modifications, check local regulations to confirm requirements.