Before we begin, you need to be familiar with the tyre specifications. The specifications of a tyre can be found on its sidewall and typically look like this:What it means? A is the Section Width. In the example above, it means the tyre has a width of 195mm. B is the Aspect Ration. It is the height of the sidewall expressed as a percentage of the width. In the example, the sidewall is 65% of the width (195), which makes it 195 x 0.65 = 126.75 mmC is the Tyre construction. R denotes radial construction, which is typical of passenger tyres. D is the Rim diameter in Inches. So 15 means that the tyre can fit rims of 15 inches. E is the Tyre Load Index. It represents the maximum weight the tyre can carry. By looking up a Load Index table, 91 (in the example) gives you a load capacity of 615kg. F is the Speed Index. It is also known as the speed rating as it tells you the maximum speed the tyre is suitable for a full load. By looking up the Speed Index table, you will see that T allows you a maximum speed of 190km/h.