Tyre size is the most important information given on the tyre. The size designation is specified as a series of numbers and letters, for example, 185/65 R 14 86 T, where:
|185||is the width of the tyre in mm|
is the aspect ratio (height to width ratio)
|R||denotes radial construction|
|14||is the rim diameter in inches|
|86||is the load index|
|T||is the speed rating.|
The speed rating shows the maximum continuous driving speed capability of the tyre. The speed rating to be selected depends on the make and model of car. The use of tyres with speed ratings that are too low can affect the driving qualities and tyres with speed ratings that are too high may reduce driving comfort.
The most important speed ratings are
Q = 160 km/h
S = 180 km/h
T = 190 km/h
H = 210 km/h
V = 240 km/h
W = 270 km/h
Y = 300 km/h
You can download a table on passenger car tyre diameter correspondence and detailed information about sidewall markings onto your computer as PDF files.
To view this data, you will need Adobe Acrobat Reader. You can download this software free of charge from the Adobe website.