Aspect ratio
The aspect ratio refers to the height of the sidewall divided by the tyre's width. Let’s take for example the following tyre size:
175/70 R13 S. In this case, 70 indicates that the tyre’s height is equal to 70% of its width. This is also known as a “70 series tyre”. Nowadays, on the tyre market, series range between 80 and 25. Tyres that have an aspect ratio of 55 or lower are regarded as “low profile tyres”.