How To Read Your Tyre Size

It’s easier than you think to understand tyre size!

What size are my tyres?

It feels good to know your tyre size when talking to your mechanic. But it’s not the only thing you’ll learn by simply looking at your tyre.

Next to the manufacturer's name and the name of the tyre (eg. a Firestone F01), there’s another set of numbers that tells us tyre size, tyre profile and how the tyre was made.

By the numbers

Example 205/40R17

  • 205 is the width of the tyre in millimetres.

  • 40 is the aspect ratio or tyre profile.

  • R means it is radial construction.

  • 17 is the diameter of the wheel rim in inches.

How to read tyre sizeHow to read tyre size

What's a tyre profile?

Your tyre profile relates to the depth of your tyre’s sidewall expressed as a percentage of the tyre’s width. 

In the above example, 205/40R17, the tyre profile is 40, meaning the depth of the sidewall is 40% of the 205mm tyre width. 

Does low profile = better performance?

Low profile tyres generally have an aspect ratio lower than 50%. Anything under 30% is considered ‘ultra low’ profile and normally associated with high performance cars seeking better cornering and on-road handling.

While ‘low’ profile tyres do generally deliver superior cornering, the compromise could be a slightly ‘harder’ ride. Not sure what tyres to choose for your vehicle? Talk to the Tony’s team about getting the right tyre fit.