How to read your tyre size | Blog
May 20, 2022
Replacing tyres is a vital part of car ownership, but you can’t just pick any old tyre up from the mechanic. To ensure your safety, it has to be the right model to fit your car and to decipher this, you will need to be able to read the size of your existing tyres. In this guide, we’ll show you how to read your tyre size.
Where to look
Tyres have a coded system moulded onto them. This can be found on the side of the tyre that faces outwards, near the rim, and should be easily spotted. It provides information on the construction of the tyre that is needed to know what it can be replaced with. Let’s say that you’ve looked at your tyre and the code reads 185/75 R 16 94 H.
How to read it
To read the tyre size, let’s begin with the first three digits that you will see. These indicate the width across the tyre. These are shown in millimetres. So, using our example, this means that the section width of the tyre is 185 millimetres.
The next part is the fourth and fifth digits of the code, which make up a two-digit number that represents a percentage. This compares the tyre’s section height with its section width. This is referred to as the aspect ratio. So, if this tyre code says the aspect ratio is 75%, it means its height is 75% of its width. To work out the exact measurement of the section height, we just work out what 75% of 185 is, which is 138. So, the height from the rim to the edge of the tyre is 138mm.
In our example, and on most modern cars, we then see the letter R. This stands for radial construction and indicates that the tyre has been made with the cord piles angled to the direction of travel. This makes the tyres stronger.
The next digits show the nominal rim diameter in inches. In this example, the rim diameter is 16 inches. This is important as the tyre will only fit on rims of the same size.
The next two digits are a code that represents the load index, which shows the maximum weight the tyre can bear. 94 represents a maximum of 670kg, but you need to check your tyre placard to decode your load index number.
The final letter following this is a symbol to indicate the speed rating; H represents a maximum speed of 210km/h. You can fit tyres with a higher speed rating than your existing tyres although it's not recommended that you go lower. If your tyre has a different letter, there are charts available online which will tell you what your maximum speed rating is.
Contact Advance Tyres Today!
Tyre sizes may seem impossible to decode at first, but once you know what you are looking for, they are simple and easy to work out. Contact us at Advance Tyres for all tyre maintenance needs, on 07 5483 9311 for Gympie and 07 4122 1693 for Maryborough.
