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Identifying the size of tyres on your car
Sidewall Markings
On the tyre sidewall you will find various codes and markings, some of which relate to the tyre size.
Tyre Sizes
Tyre sizes are made up of a number of different numbers and letters. For example tyre size 185/60 R 14 82 H is made up of the following information:
185 The tyre section width in millimetres
60 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
14 Rim diameter in inches
82 Load Index
H Speed Rating
This is all the information you need to order your tyres but if you would like to know more, read on…
Aspect Ratio
Aspect ratio is the ratio of a tyre's width to it's height. A 60 series tyre, therefore, is a tyre whose height is equal to 60% of its width.
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
ZR 240 149
Load Indices
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
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 and which specify the company, factory, mould, batch and date of production, such as, DOT DVDE MTA 129
E-Marks - Tyres for sale within the European Community must carry an E -Mark in accordance with ECE Reg 30 - e.g. E4 027550 (where 4 is the number indicating the country of approval).
Air Pressure
The main function of a tyre is to carry the load of the car. Therefore, it is vital that correct air pressure is maintained. Over-inflation will cause rapid and irregular wear.
Under-inflation will damage the tyre structure leading to possible accidents.
Improper air pressure will not allow the tyre to function within its design. For best performance always maintain the air pressure as recommended by the vehicle manufacturer and/or the tyre manufacturer.
Wheel Alignment and Balancing
A major cause of rapid tread wear is incorrect wheel alignment. Abnormal noise and vibration in the steering wheel at certain speeds is a sure sign that the wheels are out of balance.