Recently I had to replace my tyres due to wear and tear and puncture damage. A simple task you might think. I checked Yellow Pages then rang a few tyre specialists, as might be expected each recommended a different brand with prices ranging from 13 to 50+ per wheel, fitted and balanced. None of the tyre replacement specialists was able to fully explain to me the figures and codes on the tyre sidewall. So here they are:
The illustration on the left depicts an American tyre, not all this information appears on European Continental and British tyres. What invariably does appear is something like this: 175/70R13 82T. Taking this example of my tyres: 175 is the tyre section in millimetres; /70 is the aspect ratio (the height of the sidewall divided by the tyre's width); R is the construction type, radial in this case; 13 is the rim diameter in inches; 82 is the load index; and T is the speed rating. No one seemed to know what the speed rating actually meant, so here are the code letters in kilometres/miles:

Click for guidance on Tread Pattern Designs at Kumho Tyre Information A8 40/25
B 50/31
D 70/43
J 100/62
L 120/74
M 130/81
N 140/87
P 150/93
Q 160/99

R 170/106
S 180/112
T 190/118
H 210/130

V 240/149
W 270/168
Y 300/186
ZR 240/149
VR 269/167

Of the ones in blue, T is the most common on modern family and fleet cars and H on higher performance cars. Clearly any below R (shown in red) are special tyres and would be dangerous on a modern car, so beware of any cheap retread offers from unscrupulous dealers.

The best technical information on tyres is available here, courtesy of Tyres Online. Another excellent site for technical information can be found at Kumho Tyres.

Peter Ghiringhelli.

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Please note that I cannot accept liability for the use or misuse of any of the information given on tyres. The data on this page was obtained from a variety of sources, including tyre manufacturers, and is applicable to the UK only. Any information provided by me is given on the understanding that you acknowledge this disclaimer.