At first glance the lettering on the side of the tyre may look complicated but its their for a purpose. The lettering explains the exact specification of the tyre you have on your car. It tells you anything that you may need to know about your tyres.

A tyre speed rating (i.e. S) is the maximum speed for which the tyre is rated. For example, the S rating identifies speeds up to 112 mph.

Speed ratings are based on scientific tests where the tyre is run at speeds in 6.2 mph steps in 10 minute increments until the required speed has been met.

You will find your size/load/speed rating on the side of your tyre in a series of numbers - as follows:

205/55 R17 91 W

So what does that all mean?

205 = Width of the tyre in millimetres

55 = Height of the tyre sidewall as a percentage of the width. In this case 55% of 205mm. Also know as the aspect ratio.

R = Radial Construction.

17 = The diameter of the tyre's inner rim in inches

91 = Load Capacity of Tyre

W = Speed Symbol. Indicates the max. speed for the tyre at full load. In this case 168mph.

It is IMPORTANT that you check your speed rating and the 'Load Rating' before buying your tyres - as choosing a lower tyre speed or load rating could INVALIDATE your INSURANCE.