Tyre Size Guidelines
The tyre width is shown in millimetres and is the width from one side of the tyre to the other. Wider tyres give the car more contact with the road and therefore more traction.
The tyre profile is actually a ratio, not a metric measurement. The profile is the ratio of tyre width to profile height shown as a percentage.
All tyres have a speed rating letter. The letter denotes a maximum speed that the tyre can sustain for a 10 minute period without falling to pieces. Each speed rating is 10Km/h above the previous. This is a very important parameter, as there is a legal requirement to fit tyres to your vehicle with the correct speed rating.