On the sidewall of your tyres you will see something similar to this;

In this example we are looking at a 205/55R16 91W

This tells us the tyre size, load index and speed rating of your tyres.

205 = Section width of your tyre in millimetres (205mm)

55 = Aspect ratio of your tyre (the sidewall height as a % of the section width)

R = Radial

16 = Rim diameter in inches (16 inch)

91 = Load Index (load capacity i.e. maximum weight your tyre can carry)

W = Speed Rating

For further information on tyre speed and load ratings please see tables below.

Speed Index Table

Load index table