Choosing the correct tyre size is essential for your vehicle’s safety, handling, fuel efficiency, and overall performance. At Onyx Tyres, we help Australian drivers find the right tyres for every type of vehicle, from passenger cars and SUVs to commercial vehicles and electric cars. If you’re replacing worn tyres or upgrading to a new set, understanding your tyre size ensures you choose tyres that fit correctly and perform as the manufacturer intended. In this guide, we’ll explain where to find your tyre size, what the numbers on the sidewall mean, and why choosing the right size matters.
Why Your Tyre Size Matters
Your vehicle’s recommended tyre size is carefully selected by the manufacturer to deliver the best balance of safety, comfort, braking, and fuel economy. Installing the wrong tyre size can affect steering, increase tyre wear, reduce fuel efficiency, and even impact your speedometer accuracy.
Using the correct tyre size also ensures proper contact with the road, giving you better grip in both wet and dry conditions while maintaining stable handling during everyday driving.
Where Can You Find Your Tyre Size?
Finding your tyre size is easier than many drivers think. You can usually find it in one of the following places.
- On the Tyre Sidewall – The easiest place to locate your tyre size is on the sidewall of your current tyre. You’ll see a combination of numbers and letters similar to this:
- 225/45 R17 94W – This code contains all the information you need to identify the correct tyre size for your vehicle.
- Driver’s Door Placard – Most vehicles have a tyre information sticker inside the driver’s door frame or door jamb. This placard lists the recommended tyre size, tyre pressure, and load specifications provided by the manufacturer.
- Vehicle Owner’s Manual – Your owner’s manual also includes the recommended tyre size and other important tyre specifications for your vehicle.
- Ask a Tyre Professional – If you’re still unsure, a tyre specialist can quickly identify the correct tyre size based on your vehicle’s make, model, and year.
How to Read Your Tyre Size
A tyre size such as 225/45 R17 94W may seem confusing at first, but each part has a specific meaning.
225 – Tyre Width – The first number represents the tyre width in millimetres. In this example, the tyre is 225 mm wide from one sidewall to the other. A wider tyre generally provides more road contact, which can improve grip and handling.
45 – Aspect Ratio – The second number is the aspect ratio. It indicates the height of the tyre’s sidewall as a percentage of its width. A 45 aspect ratio means the sidewall height is 45% of the tyre’s width. Lower aspect ratios usually provide sportier handling, while higher profiles offer a smoother and more comfortable ride.
R – Radial Construction – The letter R stands for radial construction, which is the standard design used in almost all modern passenger vehicle tyres. Radial tyres offer better durability, improved fuel efficiency, and a more comfortable driving experience.
17 – Wheel Diameter – The number following the letter represents the wheel diameter in inches. In this example, the tyre is designed to fit a 17-inch wheel.
94 – Load Index – The load index indicates the maximum weight each tyre can safely carry when properly inflated.
It is important to choose tyres with a load index that meets or exceeds your vehicle manufacturer’s recommendation.
W – Speed Rating – The final letter indicates the tyre’s maximum approved speed under ideal conditions.
Common speed ratings include:
- T – Up to 190 km/h
- H – Up to 210 km/h
- V – Up to 240 km/h
- W – Up to 270 km/h
- Y – Up to 300 km/h
Always follow the speed rating recommended for your vehicle.
Can You Change Your Tyre Size?
Some drivers choose different tyre sizes to improve appearance or performance. While minor changes may be possible, they should only be made after professional advice.
Changing tyre size can affect:
- Speedometer accuracy
- Fuel consumption
- Suspension performance
- Vehicle handling
- Braking performance
- Ground clearance
For the safest results, it’s usually best to follow the manufacturer’s recommended tyre size.
Common Tyre Size Mistakes
Many drivers accidentally purchase the wrong tyres because they overlook important specifications. Some of the most common mistakes include:
- Choosing the wrong wheel diameter
- Ignoring the load index
- Selecting an incorrect speed rating
- Mixing different tyre sizes on the same vehicle
- Buying tyres based only on price
Taking a few minutes to confirm your tyre size can help you avoid unnecessary costs and improve your driving safety.
Choosing the Right Tyres
Your driving habits and vehicle type also play an important role when selecting tyres. For daily commuting, comfort and fuel efficiency may be your priorities. SUV and 4WD owners often need tyres designed for extra durability and different road conditions, while commercial vehicles require tyres capable of carrying heavier loads. Electric vehicles benefit from tyres designed to handle additional battery weight while reducing rolling resistance to maximise driving range.
Choosing tyres that suit both your vehicle and your driving style will help you get the best performance and longest tyre life.
Final Thoughts
Knowing how to find and understand your tyre size makes replacing your tyres much easier and helps ensure your vehicle performs safely and efficiently. By checking your tyre sidewall, driver’s door placard, or owner’s manual, you can quickly identify the correct size for your vehicle.
If you’re unsure which tyres are right for your car, SUV, ute, or commercial vehicle, the team at Onyx Tyres is here to help. With expert advice and a wide selection of quality tyres, you can confidently choose the right fit for safer, smoother, and more reliable driving on Australian roads.