When buying a new tire or when we just want to check the parameters and performances of our current vehicle tires, we need to read the tire side markings. The numbers and symbols found on the sidewall of every tire give significant details about their size, performance and manufacturing dates.
The most common and visible marking is the size marking. The symbol for size has the following format:
TireWidth [mm] / AspectRatio [%] Construction RimDiameter [in]
Example: 225/60R18
The tire width (255), in millimeters, is the distance measured from sidewall to sidewall.
The aspect ratio (60), in percentage, is the ratio between the tire height and width.
\[\text{Aspect Ratio [%]}=\frac{\text{Tire Height [mm]}}{\text{Tire Width [mm]}} \cdot 100\]An aspect ratio of 60 means that the height of the tire is equal to 60% of the tire’s width. The higher the aspect ratio, the higher the height of the tire. Off road tires have high aspect ratio since tire height is good for rocky, bumpy roads. Sports, high performance tires have low aspect ratio, since the lower the height of the tire, the better is the stability of the vehicle and the grip of the wheel.
The construction symbol gives details about the inside layers of the tire (plies), how are they arranged across the tire. The most common type of tires is the Radial tire (R). There are also Diagonal tires (D) or Belted (B).
The wheel/rim diameter, in inches, is the external diameter of the wheel/rim. It is also the internal diameter of the tire.
The are also additional markings after the size marking. These are the load index and the speed index.
TireWidth [mm] / AspectRatio [%] Construction RimDiameter [in] LoadIndex SpeedIndex
Example: 245/40R18 97V
The load index (LI) indicates the maximum weight supported by the tire when properly inflated. For example the load index 97
means that the tire can withstand 730 kg of load (weight).
A comprehensive load index table is below:
LI | kg | LI | kg | LI | kg | LI | kg | LI | kg | LI | kg | LI | kg |
0 | 45 | 25 | 92.5 | 50 | 190 | 75 | 387 | 100 | 800 | 125 | 1650 | 150 | 3350 |
1 | 46.2 | 26 | 95 | 51 | 195 | 76 | 400 | 101 | 825 | 126 | 1700 | 151 | 3450 |
2 | 47.5 | 27 | 97.5 | 52 | 200 | 77 | 412 | 102 | 850 | 127 | 1750 | 152 | 3550 |
3 | 48.7 | 28 | 100 | 53 | 206 | 78 | 425 | 103 | 875 | 128 | 1800 | 153 | 3650 |
4 | 50 | 29 | 103 | 54 | 212 | 79 | 437 | 104 | 900 | 129 | 1850 | 154 | 3750 |
5 | 51 | 30 | 106 | 55 | 218 | 80 | 450 | 105 | 925 | 130 | 1900 | 155 | 3850 |
6 | 53 | 31 | 109 | 56 | 224 | 81 | 462 | 106 | 950 | 131 | 1950 | 156 | 4000 |
7 | 54.5 | 32 | 112 | 57 | 230 | 82 | 475 | 107 | 975 | 132 | 2000 | 157 | 4125 |
8 | 56 | 33 | 115 | 58 | 238 | 83 | 487 | 108 | 1000 | 133 | 2060 | 158 | 4250 |
9 | 58 | 34 | 118 | 59 | 243 | 84 | 500 | 109 | 1030 | 134 | 2120 | 159 | 4375 |
10 | 60 | 35 | 121 | 60 | 250 | 85 | 515 | 110 | 1060 | 135 | 2180 | 160 | 4500 |
11 | 61.5 | 36 | 125 | 61 | 257 | 86 | 530 | 111 | 1090 | 136 | 2240 | 161 | 4625 |
12 | 63 | 37 | 128 | 62 | 265 | 87 | 545 | 112 | 1120 | 137 | 2300 | 162 | 4750 |
13 | 65 | 38 | 132 | 63 | 272 | 88 | 560 | 113 | 1150 | 138 | 2360 | 163 | 4875 |
14 | 67 | 39 | 136 | 64 | 280 | 89 | 580 | 114 | 1180 | 139 | 2430 | 164 | 5000 |
15 | 69 | 40 | 140 | 65 | 290 | 90 | 600 | 115 | 1215 | 140 | 2500 | 165 | 5150 |
16 | 71 | 41 | 145 | 66 | 300 | 91 | 615 | 116 | 1250 | 141 | 2575 | 166 | 5300 |
17 | 73 | 42 | 150 | 67 | 307 | 92 | 630 | 117 | 1285 | 142 | 2650 | 167 | 5450 |
18 | 75 | 43 | 155 | 68 | 315 | 93 | 650 | 118 | 1320 | 143 | 2725 | 168 | 5600 |
19 | 77.5 | 44 | 160 | 69 | 325 | 94 | 670 | 119 | 1360 | 144 | 2800 | 169 | 5800 |
20 | 80 | 45 | 165 | 70 | 335 | 95 | 690 | 120 | 1400 | 145 | 2900 | 170 | 6000 |
21 | 82.5 | 46 | 170 | 71 | 345 | 96 | 710 | 121 | 1450 | 146 | 3000 | 171 | 6150 |
22 | 85 | 47 | 175 | 72 | 355 | 97 | 730 | 122 | 1500 | 147 | 3075 | 172 | 6300 |
23 | 87.5 | 48 | 180 | 73 | 365 | 98 | 750 | 123 | 1550 | 148 | 3150 | 173 | 6500 |
24 | 90 | 49 | 185 | 74 | 375 | 99 | 775 | 124 | 1600 | 149 | 3250 | 174 | 6700 |
The speed index (SI) or speed rating, indicates the maximum speed which can be withstand by the tire. Usually the speed index of the tire is matching the maximum speed of the vehicle. For example, the speed index V
means that the maximum speed capability of the tire is 240 kph.
A comprehensive speed index table is below:
SI | Maximum Speed [kph] | SI | Maximum Speed [kph] |
A1 | 5 | L | 120 |
A2 | 10 | M | 130 |
A3 | 15 | N | 140 |
A4 | 20 | p | 150 |
A5 | 25 | Q | 160 |
A6 | 30 | R | 170 |
A7 | 35 | S | 180 |
A8 | 40 | T | 190 |
B | 50 | U | 200 |
C | 60 | H | 210 |
D | 65 | V | 240 |
E | 70 | Z | over 240 |
F | 80 | W | 270 |
G | 90 | (W) | over 270 |
J | 100 | Y | 300 |
K | 110 | (Y) | over 300 |
The manufacturing date of the tire is usually displayed by four digits inside an oval filed. For example 2514 means that the tire was produced in the 25th week of the year 2014.
A special marking is for winter tires. If the tire has the symbols M+S (Mud and Snow), it’s designed to achieve better values for handling and traction in winter conditions, compared with a summer tire (without M+S marking).
The snow flake symbol also known as 3PMSF (Three Peak Mountain Snow Flake) symbol is is also related to winter tires and it’s required by North American legislation.
Tires can also have traction and temperature grades. The traction grade indicates the wet traction performance of the tire under controlled testing conditions. A tire with an “AA” traction rating has outstanding traction performance in wet conditions. Traction grades can be: AA, A, B or C
Temperature grade indicates the capacity of the tire to withstand high temperature. A tire with a high temperature grade can operate at higher vehicle speeds. The best temperature grade is A, followed by B (medium) and C (low).
Treadwear grades are set based on standardized government tests, which predict the expected treadwear of a tire. For example, a tire with a treadwear grade of 220 should last twice as long as a tire with a treadwear grade of 110.
Introduced by the Economic Commission for Europe (ECE), the tire E mark is now mandatory on all European tires. It also signals that the tire meets certain requirements in terms of sizing, performance and marking. For example E4 enclosed in a circle means that the tire was produced and approved in Netherlands.
A comprehensive E mark table is below:
Code | Country | Code | Country |
E1 | Germany | E21 | Portugal |
E2 | France | E22 | Russian Federation |
E3 | Italy | E23 | Greece |
E4 | Netherlands | E24 | Ireland |
E5 | Sweden | E25 | Croatia |
E6 | Belgium | E26 | Slovenia |
E7 | Hungary | E27 | Slovakia |
E8 | Czech Republic | E28 | Belarus |
E9 | Spain | E29 | Estonia |
E10 | Yugoslavia | E31 | Bosnia and Herzegovina |
E11 | United Kingdom | E32 | Latvia |
E12 | Austria | E34 | Bulgaria |
E13 | Luxembourg | E37 | Turkey |
E14 | Switzerland | E40 | Macedonia |
E16 | Norway | E43 | Japan |
E17 | Finland | E45 | Australia |
E18 | Denmark | E46 | Ukraine |
E19 | Romania | E47 | South Africa |
E20 | Poland | E48 | New Zealand |
Starting with November 2012 all new tires sold in the European Union (EU) must be provided with a standardized tire label. The information on the label is related to three tire properties:
- rolling resistance
- grip in wet conditions
- road noise
The labels are divided in three categories: C1 (passenger vehicles), C2 (light utility vehicles) and C (heavy commercial vehicles). Best grade is A, worst is G.
The maximum permissible inflation pressure (e.g. 45 psi = 3.1 bar) is the maximum air pressure at which the tire can be inflated. This pressure should be much higher than the nominal working pressure of the tire (e.g. 2.1 bar).
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