Every tyre carries its size printed on the sidewall as a short string of numbers and letters, something like 235/60R18 100H. It looks technical, but once you know what each part means, ordering the right tyre for your vehicle becomes straightforward, and it means we can quote you accurately from a single line of text.
Breaking down 235/60R18 100H
The first number, 235, is the tyre's width in millimetres, measured from sidewall to sidewall. The second number, 60, is the aspect ratio: the height of the tyre's cross-section as a percentage of its width. In this case, the sidewall height is 60 percent of 235mm.
The letter R stands for radial construction, which is how almost every modern passenger and light-truck tyre is built. The number that follows, 18, is the wheel diameter in inches that the tyre is designed to fit. Finally, 100H is the load index and speed rating: 100 relates to the maximum weight the tyre can carry per tyre, and H is the maximum speed the tyre is rated for under that load.
Where to find it
You'll find this information moulded into the sidewall of your current tyres, and it's also usually printed on a sticker inside the driver's door frame or in your vehicle's handbook. If you're not sure which number is which, a photo of the sidewall is often enough for us to work it out for you.
Why it matters when you order
Getting the size right matters for more than just fit. The wrong load index or speed rating can affect how your vehicle handles and how it's legally allowed to be driven, and even a slightly different width or aspect ratio can throw off your speedometer or clearance around the wheel arch. That's why our quote form asks for your tyre size if you know it, so we can match you with the exact right tyre, or confirm the best option if you're upgrading or changing your setup.
- Width (mm) — the first number in the sequence
- Aspect ratio (%) — sidewall height relative to width
- Construction type — almost always R for radial
- Wheel diameter (inches) — must match your rim
- Load index & speed rating — the final numbers and letter
Not sure what you need?
If you can't find the numbers, or you're just not confident reading them, send us your vehicle make and model through our quote form instead. We can look up the correct factory tyre size for most vehicles and quote you from there.
Ready for your next set of tyres?
Send us your tyre size or vehicle details and we'll come back with a sharp price.