What do your tyre sidewall markings mean?
06 July 2015
All of the important information that you need to know about your tyre is printed on the sidewall, but do you know how to read it? Setyres have put together a helpful guide to help you to understand what all the numbers and symbols on your tyres mean.
Tyre Brand
The tyre manufacturer is easily identifiable on the sidewall.
Tyre Size
The size of a tyre is clearly printed on the sidewall and looks something like this 205 / 55 / R18. This string of numbers indicates the sizes and dimensions of the tyre.
205 - This number is the nominal width which is measured in milimetres. It is taken from sidewall to sidewall and so gives the accurate cross-section of the width.
55 - This is the aspect ratio and measures the height of the sidewall. It is a percentage of the nominal section width.
R - The 'R' in this construction indicates radial tyre construction, almost every new tyre built today is a radial tyre.
18 - This indicates the wheel diameter which is measured in inches.
Tyre Pattern
Each manufacturer has a range of tread patterns unique to their brand. You can find the name of the tread pattern on the sidewall and often the range that the tyre has come from too.
Tread Wear Indicator
The letters TWI highlight the location of the tyre's tread wear indicators. The indicator is set at 1.6mm at least, which is the minimum legal tread depth in the UK. It is important that you check these indicators regularly to ensure that the tread is sufficiently deep. When your tyre tread wears down and reaches the indicator, legally it's time to have the tyre replaced. Take a look here if you need more guidance on checking the tread depth of your tyres.
Maximum Pressure
The maximum pressure limit indicates the amount of pressure that the tyre can withstand. This figure should not be confused for the recommended inflation pressure which can be found in your vehicle handbook.
Load Index
The load index for your tyre can be found at the end of the tyre size string eg. 205 / 55 / R18 105V. This code indicates the maximum load that a tyre can carry and relates to the table below. For example, using the table, if a tyre has a load index of 105 then the maximum load would be 925kg.
Speed Index
The speed index of the tyre is the letter following the load index eg. 205 / 55 / R18 / 105V. This letter corresponds to a maximum speed that the tyre can service and can be identified using the following table. For example, using the table, if a tyre had a speed rating of V then the maximum speed would be 149mph.
Mounting Direction
Asymmetric tyres must be fitted the right way on a wheel to benefit from the tread block arrangement. Similarly, directional tyres are designed to rotate in one direction only. Therefore the sidewalls of these tyres will be clearly marked with an indicator to show which way they need to be fitted. Incorrect fitting can lead to MOT failure.
If you are searching for new tyres take a look online at our wide range of products. Alternatively, find your nearest branch and arrange a fitting at a time to suit you. If you are unsure about your tyre safety don't hesitate to call in to your local Setyres centre and allow our fully trained professional staff to perform a free tyre check for you.