Tyres Marking

Sidewall Markings

On the sidewall of a tyre you will find various codes and markings. The list below aims to simplify the coding system and allow you, the user, to understand the valuable information imprinted on the sidewall.

Tyre Sizes

Tyre sizes are made up of a number of different numbers and letters. For example tyre size 175/70 R 13 82 T is made up of the following information:

175	The tyre section width in millimetres (That is the width of the tyre tread)
70	The aspect ratio in % (the height of the sidewall divided by the tyre's width)
R	Denotes the tyre's construction type - in this case it's a radial
13	Rim diameter in inches
82	Load Index
T	Speed Rating

Tyre Age

Tyres carry a three digit age code on the sidewall indicating the month and year of manufacture. For example 129 means the tyre was manufactured in December 1999.

Other Markings

M&S - Identifies Mud and Snow tyres

DOT Codes - Coding satisfying the requirements of the US Department of Transportation contain a mixture of letters and numbers such as DOT DVDE MTA 129. These identify the place of manufacture.

E-Marks - Tyres for sale in the European Community must carry an E -Mark in accordance with ECE Reg 30 - eg E4 027550.

Load Indices

Drivers should be aware that these ratings exist to protect the public from the possible outcome of overloading a tyre. Also, that these load ratings apply to a properly inflated tyre.

Overloading a tyre - either by carrying more weight than it is designed to carry, or by running at a lower than specified pressure, can cause heat build up that can destroy the tyre. Even at low speeds a blow out can be fatal.

It is a breach of Construction and Use Regulations to run on overloaded tyres or tyres with the wrong load rating. The load-index figure imprinted on the sidewall of the tyre denotes the maximum load capacity of a tyre when driven at maximum speed.

A list of load indices and maximum weights is give below:

Li	kg	Li	kg
65	290	94	670
66	300	95	690
67	307	96	710
68	315	97	730
69	325	98	750
70	335	99	775
71	345	100	800
72	355	101	825
73	365	102	850
74	375	103	875
75	387	104	900
76	400	105	925
77	412	106	950
78	425	107	975
79	237	108	1000
80	450	109	1030
81	462	110	1060
82	475	111	1090
83	487	112	1120
84	500	113	1150
85	515	114	1180
86	530	115	1215
87	545	116	1250
88	560	117	1285
89	580	118	1320
90	600	119	1360
91	615
92	630
93	650

Speed Ratings

All tyres carry a speed symbol in the form of a letter indicating the maximum speed for which the tyre is intended. The table below shows which speed goes with each letter.

Speed symbol	Maximum speed km/h	mph
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

It should be noted that these ratings are important in that it is a breach of Construction and Use regulations to run on tyres that are below the specified Load Index, it may also be dangerous.

Additionally, if your car is fitted with W-rated tyres, and you tow a trailer, then in the UK that trailer may have T-rated tyres (if applicable), but in France your trailer tyres' rating should match that of the tow vehicle.

Aspect Ratio

Aspect ratio is the ratio of a tyre's width to it's height. A 70 series tyre, therefore, is a tyre whose height is equal to 70% of its width. Lower Profile Tyres hence have lower series numbers.

People upsizing to lower profile tyres should be aware that they will change the nature of their vehicle's handling and comfort.