Tyre Maintenance Guide

How Do Car Tyre Sizes Work?

We subject our cars to various periodic checks- Engine oil, suspension, washing and what not. But most of us end up neglecting the tyres. The physical condition of tyres plays a big role in determining the performance, ride comfort,and handling of your car. But, have you ever thought about what role the size of tyres plays?

Tyres come in different sizes,and their width also differs. Like we know, every car tyre comes with a set of numbers of codes. These numbers and codes tell everything about the dimension of the tyre, such as its width, tread, and the diameter too.

If you take a look at the sidewall of a tyre, you can easily find information like manufacturer’s name, the tyre’s name, and a set of letters and numbers. The numbers represent the size of the tyre, its performance and capabilities. To help you understand this thing in a better way,let us explain what all the numbers and letters mean. We will start from the leftmost side and then move to the right.


The three-digit number you will find on the left most side is the width of the tyre. So, if the three digits are 145 then it means the width of the tyre is 145 mm.We are talking about the sectional width, and it is represented in millimetres. It is important to mention that the tread width is basically smaller in comparison to the actual width of the tyre.

A tyre’s overall width is measured from its one side to the other one. The extra sidewall items are also included in the measurement. In fact, the raised letters and kerbing ribs are also incorporated.

Talking about the section width of a tyre, it is measured in the same way; except, the additional sidewall elements are not included in the measurement.Therefore, if you want to be more accurate with the width then it is better to consider the section width of the tyres.

The Profile

Also known as the Aspect Ratio of a tyre, the profile is basically the height of the sidewall. The profile is expressed as a ratio between the sidewall and the section width of the tyre. For example, if you are looking at a 195/55 tyre then it means that the height of this tyre is 55 percent of its width. It means the height of that tyre would be 107 mm(55% of 195 mm). Tyres that have a smaller aspect ratio are usually meant for the sports cars. They are also called low-profile tyres and offer superb handling and cornering capabilities. On the down side, such tyres do not offer a well-cushioned and comfortable ride.

Rim Size

The rim size can be best described as the measurement of a tyre’s inner diameter combined with the wheel’s outer diameter. In the code, you must not get confused the letter ‘R’ with rim size.Here the letter R represents the construction type of the tyre. R stands for Radial. Most of the modern cars come equipped with radial tyres. So, if you see R 15 in the code then it means the tyre is of radial type, having a rim diameter of 15 .

Load Capacity

Every tyre has a maximum load capacity. The same is mentioned on the sidewall of the tyre, in the form of a numerical code. The numerical figure represents the maximum load the tyre can withstand when it is being operated at its top speed. If a car tyre has a load index of 82 then it means the maximum load capacity is 475. Before you buy a tyre for your car, you must check its load index to figure out its total load carrying capacity.

Speed Rating

Just like load capacity, every tyre has a speed limit too. Like we know, more heat is generated at higher speeds. For this reason, if you are someone who loves driving at higher speeds, you must buy tyres that come with a high speed rating. The speed rating is denoted by a letter; and, every letter represents a certain speed limit. For example, if a tyre has the letter ‘Q’ on it then its maximum speed limit is 160 kmph. Likewise, the letter R means 170 kmph, and so on.

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