Tyre Size Code information

Ok so you have read out article on tyre safety and are a bit worried about the rubber you have on your classic so you want to replace like for like but what does the code on the tyres actually tell you and what do you need for your car.

Most tyre will have a code similar to the one below but what does it all mean.

185 65 H R 14

185 :- This is the width in mm from sidewall to sidewall when the tyre is unstressed

65:- This is the ratio of the sidewall height as a percentage of the width and is know as the aspect ratio.

H :- This is the speed rating for the tyre.

R:- This lets you know that the tyre is of radial construction.

14:- This is the diameter of the wheel rim in inches for some reason they mix metric and imperial measurements in the same code.

Recent development especially in Europe has moved towards the DIN standard which is the German institute for standards. This has meant a slight change to the code, for example

185 65 R 14 91 H

The only real difference is the order of the numbers and letters and the addition of a load rating in this example 91.

Speed rating

The speed rating is the maximum speed that the tyre can withstand for a 10 minute endurance test without it destroying itself and coming to pieces.

L = 75MPH
S = 113 MPH
M = 81 MPH
T = 118 MPH
N = 87 MPH
U = 125 MPH
P = 95 MPH
H = 130 MPH
Q = 100 MPH
V = 150 MPH
R = 105 MPH
W =158 MPH
Z = 150+ MPH

You should check the pressure at least every two weeks, and only when the tyres are cold. Even a short trip to the local garage will warm up the tyre and raise the pressure.



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| Updated 28 Dec-2007 |