Larger tyres, suspension lifts and bull bars are common modifications on Australian 4WDs, but they may also affect how the vehicle’s autonomous emergency braking system operates.
In January 2026, the Australian Automotive Aftermarket Association (AAAA) introduced an ADAS Vehicle Modifications Code of Conduct. The voluntary Code establishes a national test process for verifying that automatic emergency braking (AEB) continues to perform correctly after modifications involving tyres, suspension, vehicle mass, braking systems or frontal protection.
It is an important development for 4WD owners, tyre retailers and workshops working on vehicles equipped with advanced driver assistance systems, which is most of the new 4WD models sold in Australia.
Can Larger Tyres Affect AEB?
AEB combines information from cameras, radar and other sensors to calculate the distance and closing speed between a vehicle and an obstacle. If the driver does not respond to a collision warning, the system can automatically apply the brakes.
These systems are calibrated around the vehicle’s original specifications, including:
- Ride height
- Sensor position and angle
- Tyre rolling circumference
- Vehicle pitch and mass
- Braking performance
A suspension lift can change the angle of a camera or radar sensor. Larger-diameter tyres alter rolling circumference and wheel-speed information, while extra equipment can change the vehicle’s weight, pitch and stopping distance.
All of these parameters are programmed into the safety systems with tolerance ranges. Any modifications made to the vehicle do not change the programming, which could result in possible consequences, including delayed braking, false activation or reduced obstacle detection.
This does not mean larger tyres or suspension lifts are automatically unsafe. It means the vehicle’s safety systems may need to be recalibrated and tested after modification.
What Does the New Code Do?
The Code was developed by an AAAA Technical Working Group, with testing and drafting undertaken by the Auto Innovation Centre.
It does not replace existing regulations, manufacturer instructions or vehicle certification requirements. Instead, it provides a repeatable process for confirming that AEB continues to operate to the standard required by Australian Design Rule 98 (ADR 98).
Completing a full ADR 98 approval test every time a vehicle is modified would be impractical. The Code provides a shorter verification procedure that suitably equipped facilities can use to assess modified vehicles.
AAAA CEO Stuart Charity said the aftermarket industry must protect critical safety systems while continuing to make vehicles suitable for trade, towing and off-road use.
The Code applies to passenger vehicles, off-road passenger vehicles and light goods vehicles below 3.5 tonnes. This includes many of the dual-cab utes, SUVs and 4WDs commonly modified in Australia.
Which Modifications May Require Testing?
The Code identifies several changes that may affect AEB performance.
Larger Tyres
A change in tyre dimensions exceeding 50 mm may require validation.
Moving from an original equipment highway-terrain tyre to a larger all-terrain or mud-terrain fitment can significantly change the overall diameter and rolling circumference.
Tyre upgrades are usually assessed in terms of clearance, gearing, speedometer accuracy and legality. AEB performance must now be considered as well.
Suspension and Vehicle Pitch
An unladen ride-height change exceeding 50 mm may alter the angle at which cameras and radar sensors view the road.
Vehicle pitch can also change without a major suspension lift. A permanent canopy, steel tray, heavy rear load or uneven suspension modification may leave the vehicle sitting nose-up or nose-down.
Bull Bars and Frontal Protection
Bull bars, nudge bars and other frontal protection systems may obstruct or relocate radar and camera sensors.
Even products designed for a particular vehicle may require inspection, calibration or testing after installation.
Additional Vehicle Mass
Gross vehicle mass (GVM) upgrades and permanent accessories such as canopies, trays, long-range fuel tanks and touring equipment can affect stopping distance and braking performance.
Braking and Sensor Modifications
Changes to braking components, sensor positions or the bodywork surrounding an AEB sensor should also trigger further assessment.
What Does the AEB Test Measure?
The Code evaluates whether AEB responds when required without activating unnecessarily.
The system must issue a collision warning at least 0.8 seconds before automatic braking begins. The braking event must then produce peak deceleration of at least 5.0 m/s².
A separate test requires the vehicle to travel between two parked cars without applying the brakes unnecessarily.
A correctly functioning system must therefore detect a genuine obstacle, brake at the correct time and avoid unwanted intervention during normal driving.
Why ADR 98 Matters
ADR 98 introduced mandatory AEB requirements for new vehicles entering the Australian market.
Car-to-car AEB became mandatory for newly introduced models from March 2023 and for all applicable new vehicles sold from March 2025. Additional pedestrian-detection requirements are being introduced under ADR 98/01.
AEB is therefore no longer simply an optional driver-assistance feature on many newer vehicles. It forms part of the safety specification under which the vehicle entered the Australian market.
The new Code gives the aftermarket industry a practical way to manage the risk that a modification could interfere with that system.
What 4WD Owners Should Know
Owners should not assume a larger tyre or suspension lift automatically disables AEB. The system may remain active but operate differently from its factory calibration.
Warning signs can include:
- Unexpected collision warnings
- Inconsistent adaptive cruise control
- Unexplained automatic braking
- An ADAS warning light
- Braking that appears later than expected
These behaviours should be investigated by a workshop with appropriate ADAS diagnostic and calibration capabilities.
Modification legality and ADAS performance are also separate issues. A tyre or suspension change may fall within an allowable dimensional limit while still affecting a camera or radar sensor.
Owners should confirm state or territory requirements before purchasing substantially larger tyres or changing ride height. Tyre clearance, load rating, speed rating, guard coverage and certification requirements must also be considered.
What It Means for Tyre Retailers
Although voluntary, the Code establishes a clearer expectation for businesses modifying modern vehicles.
A tyre retailer fitting tyres beyond the Code’s nominated threshold should consider the effect on AEB, rather than assessing only physical clearance and load capacity.
Retailers should understand:
- Which modifications may require validation
- Where vehicle sensors are located
- When ADAS calibration may be necessary
- Which local facilities can conduct testing
- What documentation should be retained
Most tyre retailers will not need to purchase their own ADAS equipment. Establishing referral arrangements with qualified calibration and testing facilities may be the more practical approach.
For modern 4WDs, responsible fitment advice increasingly involves tyre dimensions, vehicle legality, electronic calibration and ADAS performance together.
Insurance and Documentation
Owners are generally expected to disclose significant vehicle modifications to their insurer. An undisclosed modification that affects roadworthiness or contributes to a collision may complicate a claim.
The Code does not determine insurance coverage. However, documentation showing that AEB was assessed after modification may help demonstrate that the work was completed responsibly.
Retailers should avoid guaranteeing insurance or legal compliance, but they can document the work performed, provide accurate fitment information and recommend further testing where required.
Conclusion
Australians will continue fitting larger tyres, lifting 4WDs and equipping vehicles for work, towing and touring. The new Code does not prevent those modifications.
It does make clear that modern vehicle modifications cannot be considered only in mechanical terms. Tyres, suspension, accessories and vehicle mass now interact with cameras, radar, braking controllers and software.
Tyre retailers have a responsibility to provide accurate fitment advice at the point of purchase. This includes considering tyre dimensions, load and speed ratings, clearance, applicable modification limits and any potential effect on the vehicle’s ADAS. Where further calibration, testing or engineering assessment may be required, that should be clearly explained to the customer before the tyres are fitted.
However, the retailer cannot control how the vehicle is subsequently modified, loaded or maintained. The ultimate responsibility remains with the vehicle owner to ensure their vehicle stays roadworthy, legal and compliant with the requirements of the state or territory in which it is registered.
For retailers and customers alike, the question is no longer simply whether a larger tyre fits. It is whether the complete fitment is appropriate, compliant and compatible with the vehicle’s safety systems. At the very least this should factor into the decision making process before changing important components on the vehicle.
Sources
- AAAA ADAS Modifications Code of Conduct
- AAAA Vehicle Modification Code announcement
- AAAA ADAS Code information
- National Code of Practice for Light Vehicle Construction and Modification
