Introduction to Tyre Sidewall Markings
Tyre manufacturers print important information on the sidewalls on every tyre which helps you to maintain your tyres and understand what you are looking for when you look for new tyres. Here is a summary of the information you need to know and how to read it.
The manufacturer’s name will be easily identifiable on the sidewall of your tyre. This is helpful if you need to replace your tyres and cannot remember which brand you bought your previous tyres from.
The pattern of every tyre is unique to the manufacturer your tyre belongs to. You can find the name of the tread pattern on the tyre sidewall and often the range that the tyre belongs to as well.
Tread Wear Indicator
The location of the tyre’s tread wear indicators is highlighted on the sidewall with the letters TWI. These indicators are crucial to tyre maintenance as they will help you to monitor tread wear on your tyres. It is a legal requirement that your tread depth is at least set as 1.6mm and you need to frequently check that your tyres meet this minimum. The Tread Wear Indicator on your tyre will be set to a minimum of 1.6mm, so if your tyre tread meets the indicators you must have your tyres replaced. Take a look at our advice if you need more help measuring your tyre tread.
This information is necessary when fitting a tyre. Both asymmetric and directional tyres are designed to rotate in a certain direction and mounting them in the wrong way means that they will not benefit from the tread block arrangement. Therefore there will be a clear indicator to show which way the tyres need to be fitted. Incorrect fitting can result in MOT failure.
The size of your tyre can be identified by a string of numbers printed on your tyre sidewall. This will resemble something like this: 205/55 R 16.
205 – this is the width of the tyre in millimetres. This figure is given in millimetres, so in this example the tyre would have a nominal width of 205mm.
55 – this figure is a percentage devised from the ratio of the sidewall height to the width (above). This is known as the aspect ratio or sidewall height.
R – this letter tells you how the tyre has been constructed. ‘R’ indicates that the tyre is of radial construction. Almost every new tyre built today is a radial tyre.
18 – is the nominal diameter of the wheel rim that the tyre is supposed to fit. This figure is given in inches, so in this example this tyre fits a wheel rim that is 18 inches in diameter.
Maximum Pressure & Load
There is a load index for your tyre which indicates the amount of pressure that the tyre can withstand. This information will also tell you how to adjust tyre pressure based on the weight of your load.
The maximum pressure that your tyre can withstand is indicated on the tyre sidewall. It is important that you do not confuse this figure for the recommended inflation pressure which can be located in your vehicle handbook. Over-inflated tyres can be extremely dangerous so make sure you read up on tyre pressure safety.
The load index for your tyre can be found at the end of the string of digits which indicate the size of the tyre. For example this will look like this - 205/55 R 16 105 V.
This figure indicates the maximum load that a tyre can withstand and relates to the following table:
In this example, if the tyre has a load index of 105 then the maximum load it could carry would be 925kg.
The speed index of the tyre can also be located at the end of the string of digits which indicate tyre size and load index for example 205/55 R 16 105 V. This figure indicates the maximum speed that the tyre can reach. The following table can help you to identify the highest speed that your tyre can service.
In this example, the speed rating of the tyre is V which means that it cannot exceed the speed of 149mph.