Tyre Load Identification: Understanding Load Index, Australian Design Rules (ADR) and Inflation Pressure
Tyre Load Identification is essential for ensuring your vehicle’s safety, compliance, and performance. Every tyre is designed to carry a specific maximum load at a designated inflation pressure.
When replacing tyres or upgrading to a different size, the new tyre must meet or exceed the load capacity of the Original Equipment tyre. This requirement is detailed on the vehicle’s Australian Design Rule (ADR) tyre placard.
Where to Find Tyre Load Information
Tyre load capacity is legally required to be marked on both sidewalls. You may see this expressed as:
A Load Index number
Maximum load in kilograms
Corresponding inflation pressure
Tyre Profile (Aspect Ratio Explained)
The tyre profile, or aspect ratio, describes the relationship between tyre height and width.
Aspect Ratio = Section Height ÷ Section Width
It is expressed as a percentage and is important when maintaining vehicle compliance and load performance.
From Ply Rating to Load Index
Historically, tyres used a Ply Rating system to indicate strength and load capability. However, this could be misleading because identical ply ratings in different tyre sizes did not represent the same load capacity.
The modern International Load Index system provides clarity. Each Load Index number corresponds to a specific kilogram rating, ensuring consistency across tyre sizes and manufacturers.
Why Inflation Pressure Matters
Tyre load capacity is directly affected by inflation pressure. As pressure decreases, the tyre’s ability to carry load also decreases.
Running a fully loaded vehicle on underinflated tyres can cause:
Excessive heat build-up
Sidewall damage
Premature wear
Tyre failure
Always ensure tyres are inflated according to the manufacturer’s recommendations when carrying maximum loads.
For comprehensive load and inflation data, consult the Tyre & Rim Association of Australia Standards Manual or speak with a qualified tyre professional.