Take a walk around your car and look closely at the sidewall of any tyre. You'll spot a string of numbers and letters that looks a bit like a code - because, in a way, it is. Every figure on that sidewall tells you something important about the tyre: its size, how much weight it can carry, and how fast it's rated to go. Knowing how to read it means you'll always know exactly what's fitted to your car, and what to look for when it's time to replace it.
Breaking down the tyre size code
A typical marking looks something like 205/55R16 91V. Here's what each part means:
- 205 - the tyre's width in millimetres, measured from sidewall to sidewall.
- 55 - the aspect ratio, meaning the height of the sidewall as a percentage of the tyre's width. In this case, the sidewall height is 55% of 205mm.
- R - stands for radial construction, which is standard on virtually all modern passenger tyres.
- 16 - the diameter, in inches, of the wheel rim the tyre is designed to fit.
Load index: how much weight it can carry
After the size comes a number known as the load index - in our example, that's the 91. This isn't a weight in kilograms itself, but a code that corresponds to a maximum load capacity per tyre when correctly inflated. Most passenger vehicle tyres carry a load index somewhere between the low 60s and low 100s, with higher numbers meaning a higher weight capacity. If you tow a caravan, carry heavy tools for work, or often load the car with family and gear, it's worth checking that your tyres' load index matches or exceeds what your vehicle manufacturer specifies on the compliance placard (usually found on the driver's door jamb).
Speed rating: the letter that follows
The final letter - V in our example - is the speed rating. It indicates the maximum speed a tyre is designed to sustain under its rated load, under controlled conditions. Common ratings you'll see on everyday Australian cars include S, T, H, V and W, each corresponding to a progressively higher top speed. This doesn't mean you should be driving anywhere near that limit on public roads, but it does matter for tyre selection: fitting a tyre with a lower speed rating than your car originally came with can affect handling characteristics and, in some cases, insurance cover.
Why it matters when replacing tyres
When it's time for new rubber, it can be tempting to save a little money on a tyre that "looks about the same size." But mismatched load or speed ratings can genuinely compromise safety and are generally not compliant with Australian standards or manufacturer requirements. As a rule of thumb, always match or exceed the original size, load index and speed rating listed on your vehicle's tyre placard, unless a qualified fitter has a specific reason to recommend otherwise.
Other markings worth knowing
A few other things you might notice on the sidewall:
- A DOT code ending in four digits showing the week and year of manufacture (for example, "2324" means the 23rd week of 2024).
- M+S or a snowflake symbol, indicating suitability for mud, snow or colder conditions.
- Directional arrows, showing the tyre must be fitted a certain way around for tread pattern performance.
Getting familiar with these markings makes it much easier to have an informed conversation next time you're due for new tyres, and helps you spot when something doesn't quite match your vehicle's requirements. If you're ever unsure what your car needs, or want a second opinion before buying, the team at Global Tyres Geelong in North Geelong can check your current tyres against your vehicle's placard and talk you through the right options for the way you drive.