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What Do The Numbers On Tyres Mean?


Close up of the number code on the sidewall of car tyre with alloy wheel, Tyre Sidewall Markings.

People see lots of different numbers on the side of a wheel, get all confused and then when it comes to being asked about their tyre size, they have no idea and go bright red in the face. Keep reading to find out how to break it down simply and remember your tyre size in no time.

Tyre Size

The tyre size can be found on the side of the wheel and is all of the letters and numbers combined. For example, the one in the image to the right is 245/45R18. This is just one of the many different tyre sizes, so it is good to practise to check in your vehicle’s handbook to make sure the right size has been fitted.

Tyre Width

The tyre width is simple. This is the first three digits on the side of the tyre that displays the width in millimetres. Like the tyre above measuring 245, this would be 245mm across the tread, from sidewall to sidewall. 

Aspect Ratio

The aspect ratio is the fourth and fifth digits of the tyre’s sidewall, that follow straight after the tyre width. This is the height of the tyre sidewall as a percentage of the tyre’s width. So once again using our image, the aspect ratio of 45 would mean that the profile height is 45% of the tyre’s width.

Radial

All radial tyres are marked with the letter R. These types of tyres are designed with the cord plies positioned at a 90-degree angle to the direction of travel. This gives the tyre additional strength when travelling. This represents the letter in the image.  

Wheel Diameter

The next two digits after the letter are the size of the wheel rim that the tyre can be fitted onto. This also represents the diameter of the tyre from bead to bead. Therefore, the above tyre with the number 18, will fit on an 18-inch wheel rim.

Load Index & Speed Rating

Last but not least are the last couple of numbers and letters on the tyre’s sidewall. The load index of your tyre relates to the maximum amount of weight it can carry. For example in the tyre above, it has a load index of 100 (800kg). The speed rating is the letter that can be found after the load index number and represents the maximum speed of a tyre when correctly inflated and being used under load. The above tyre, for example, has a speed rating of Y (300km/h). 

The reason for including the load index and speed rating together is because they should both be looked at together when wanting to buy new tyres. Also, check the manufacturers’ recommendations. 

There you have it, it really is that simple. If you have any other queries, Goodyear has some more really in-depth information on everything sidewalls, so make sure you check out that link. To check out our best 4×4 tyres for cold weather blog click here, or for any other tips and guides in keeping your tyres in great condition, visit our official blog

  • What Do The Numbers On Tyres Mean?
  • What Do The Numbers On Tyres Mean?

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