The speed rating of a tyre is indicated by a letter at the end of the tyre size on the sidewall of the tyre, and specifies the maximum speed your tyre is capable of maintaining.

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For example a tyre with a speed rating of "W" can reach speeds of up to 168mph.

The load rating of a tyre is usually found after the diameter reading and before the speed rating on the sidewall marking.

A tyre's speed rating is the result of specific tests ran by engineers. These involve running the tyre at 6.2mph steps in ten minute increments until the required speed has been met.

If your car is fitted with a tyre with a lower speed rating than is appropriate for your vehicle you could invalidate your insurance policy, therefore it is essential you check your car's speed rating before purchasing new tyres.

The table below shows the maximum speed in mph of each speed rating.

Sidewall Marking	Explanation
N	87
P	93
Q	99
R	106
S	112
T	118
U	124
H	130
V	149
Z	150+
W	168
Y	186