When purchasing new tyres you will often be asked what size you need. The garage may have a system where they can look up the tyres for your vehicle but if you have had different aftermarket alloys fitted or want a different size tyre to what is standard then you will need to have this information to hand.
A tyre has three numbers such as 105/55/R15 written on the side of them. The first number indicates the width the second number indicates the profile and the third number indicates the tyres size in inches. After this you may notice another set of reading; a number followed by a letter. The number indicates the loading rating. This number is linked to a table which tells you the load that each tyre can carry. Remember this is times by four (as long as all tyres are the same) when you are working out what load the total vehicle can carry.
The final reading is the speed rating. This is shown by a letter and again is a reference to a rating on a separate table. An R rating, for example, would be a maximum speed of 106mph. It is important to not only check the size but also the other ratings on the tyre when purchasing new ones.