Each tyre on your vehicle carries an imprint of various codes and numbers. While this can be confusing to understand, tyre markings are important and carry a specific purpose. These markings are crucial when it comes to replacing the tyre, so it’s worth taking the time to become familiar with what these tyre codes mean.
Deciphering The Code
Here's a quick guide to the important numbers, letters, codes and acronyms that you'll find printed on your tyre sidewall.
The main piece of information is the size of the tyre. There are many different variations, but in the UK, the most common dimensions are 205/55R16.
Tyre Width And Aspect Ratio
The first three digits give the width of the tyre in millimetres. Using the above example, this is 205mm, and the next two explain what’s known as the aspect ratio. In this case, it is 55mm from the rim of the tyre to the tread.
The R in the tyre marking indicates that this is a radial tyre. This refers to the way the tyre is made. Put simply, a radial tyre is constructed in a way which means there is less heat buildup. As a result, it provides a more comfortable drive.
The rim diameter is measured in inches and describes the diameter of the tyre's inner rim. In the example above, the rim diameter is 15 inches.
There will be another number followed by a letter. Usually, this is 97 W. The number is the tyre load index and indicates the maximum weight the tyre can safely carry when it is fully inflated.
The letter at the end of the code is the tyre speed rating. This relates to the maximum speed the car can safely travel with the given load index.
When you are buying tyres, you should refer to the vehicle handbook to check the speed rating of your car. It’s important to get it right, because if you are involved in an accident and it emerges that the tyres on the vehicle do not comply with the manufacturer’s recommendation, the insurance company may not pay out.
The speed rating can range from A to Y, with Y being the top speed of 300 kilometres per hour.
The final piece of information is the tyre manufacturing date. This is displayed as a string of letters and numbers, starting DOT to confirm the tyre complies with Department of Transport standards. The letters are followed by an eight-digit serial number which shows where the tyre was made, and the final four digits show when this was. For example, a tyre marked 0819 shows that it was made in the eighth week of 2019.
The letters RF on the tyre means that the side wall has been reinforced for additional driver safety. Alternatively, some tyres bear the mark EXT to signify that they are Extra Load tyres.
The tyre may also feature a marking to indicate it is a run flat model. This means that if it loses pressure, the tyre can be driven a short distance to a place where it is safe to replace the tyre.There are various different markings to show this depending on the tyre model. For example, Goodyear tyres may feature ROF to symbolise its RunOnFlat technology, while Continental tyres may feature SSR, which stands for Self Supporting Run Flat.
The next part of the code shows the type of car the tyre has been made for. Major manufacturers have specific run flat tyres designed for their vehicles and each has its own code.