How to read a tyre

After understanding the classification of tyres, the next important aspect we need to look into is how to read them. The tyres speak a coded language which can be seen on the sidewall. Deciphering this code can give us a clear understanding of the tyres affixed to your car. Some are easy to comprehend, while some of the markings require proper understanding and numbered reference indices to decipher the required data conveyed through it. Here, we shall discuss how to figure out the black toroid your car is sitting on right now.

Decoding the Tyre

Firstly, if you look at the sidewall of the tyre, you’ll notice a lot of markings/coding.

For example, the sidewall of your tyre must read something like this – “215/65 R15”.

Apart from this code, the markings would also include the manufacturer’s name, logo, directional arrows, approval ratings, inflation pressure, and few other important details which we’ll look into later. But first, let us decode the “215/65 R15”.

215 – Width. This number is the maximum width of the tyre. It is measured in millimetres from sidewall to sidewall. This width is standardised by the manufacturer depending on the vehicle. It plays an important role in vehicle handling, traction, and fuel consumption and hence needs to be taken care of when choosing new tyres.

65 – Aspect Ratio. This number following the slash is called the Aspect Ratio. This is the ratio of the height of the tyre's cross-section to its width. For example – 65 means that the height is equal to 65 per cent of the tyre's width. If the aspect ratio is higher, the sidewall of a tyre will be taller. Heavy vehicles have tyres with aspect ratios as high as 95 per cent. A higher aspect ratio may compromise handling, but it provides a more comfortable ride. Meanwhile, high-performance cars have a low aspect ratio, thus providing better handling and reduced rolling around the corners, while compromising on ride comfort. Manufacturers strive to balance the aspect ratio to provide a fine poise between handling and comfort.

R – Construction. The alphabet following the aspect ratio indicates the tyre construction. The R, in this case, stands for Radial. B will indicate that the tyre is a bias-ply type tyre. The construction of the tyre helps us understand the characteristic of the tyre.

15 – Wheel Diameter. The number here denotes the diameter of the wheel. It is the OD of the rim/alloy that will be wrapped around by the tyre. This dimension is the most important number here since the selection of the tyre depends on the size of the rim.

Miscellaneous Markings

Apart from these, as mentioned earlier, you can find other information such as –

P – Application. The first alphabet, in this case, is P which indicates the application of tyre. P stands for the passenger in this case. An ‘LT’ indicates the tyre would be for a light truck with a heavier load rating and so on.

95 – Load Index. The load index relates to the maximum load-carrying capacity of the tyre. The lower profile tyres tend to have lower load ratings compared to higher-profile ones. Fitting an incorrect load rating will seriously compromise safety and can result in a serious accident. This number is just an index and needs to be checked with the corresponding weight (in kgs) in the manufacturer’s tabloids. For instance, a load index of 95 here corresponds to the 690kg of load-carrying capacity of the tyres.

H – Speed Rating. Similar to the load index, the speed rating is the maximum service speed your tyre is capable of maintaining. The speed rating will give you the speed your tyre can endure without failure. Speed ratings are specific for passenger car tyres and not light truck tyres since LT marked tyres are not speed rated.It is essential to keep in mind the corresponding speeds to the speed rating before pushing the car to its limits, to prevent unforeseen failures.

Directional arrows – In a unidirectional tyre, it is necessary to fit the tyre in a particular forward direction. Hence the arrow helps to fit the tyre facing the right direction. Asymmetrical tyres have ‘in/out’ mentioned since it needs to be fitted with a bigger tread, half on the outside wall for proper functioning.

Date of manufacturing – Some manufacturers provide the month and year the tyre was built. Since it’s made of rubber, deterioration over a certain period of time can lead to reduced quality of the tyre.

Inflation pressure (in PSI) – This is the appropriate pressure that the tyre needs to maintain. It has a huge impact on tyre performance and it should be taken care of in order to extract optimum performance, fuel economy, wear and tear and prolong the tyre life.

Temperature indicator – The minimum and maximum temperature range the tyre could sustain is indicated so as to not take the tyre beyond its working temperatures.

Approval signature – The approved signature for the authority assuring the tyre has passed inspection and is compliant with all the regulations.

Know more about tyres here.