How to Read Your Tyre Size

What's my tyre size?

Along with the manufacturer's name and the name of the tyre (e.g. Firestone F01), there's always a set of numbers and letters that relate to the size of the tyre. Here's a rundown on what those numbers mean:

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 your tyre size


What's a tyre's profile?

This relates to the depth of the sidewall (the wall at the side of the tyre). The profile is expressed as a percentage of the tyre's width. Eg. Our 205/40R17 tyre has a profile or sidewall that is 40% of the 205mm (width). A low profile tyre is generally 50% or below, down to as little as 30% with ultra low profile tyres. Higher performance vehicles are usually fitted with tyres that have lower profiles. While low profile tyres give you greater control and better handling on corners, they can give a slightly harder ride. Also, going to a lower profile on the same size wheels will alter your speedometer reading so you'll need to fix that up before you hit the road. Talk to us and we can help you get the right fitment.


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