Provided here, for your benefit, are simple definitions of technical tyre terms that will enable you to understand the technology that goes into a tyre. Learn what each part of a tyre does, and get tyre-savvy!

Tyre Placard

1. A vehicle's original tyre and wheel specifications are detailed on a placard affixed to all vehicles manufactured on or after the 1st of January 1973.
   
   
2. The tyres conform to specific load carrying specifications as recommended on the vehicle manufacturer's tyre placard, as required by Australian Design Rule 23 (ADR23).
   
   
3. Tyres should be appropriate to the type and size of rim fitted to the vehicle.

Decoding all that information on the sidewall

All numbers, letters, symbols, mysterious codes. Here's the important stuff:

A : Manufacturer or brand name, and commercial name or identity.
B & J : Tyre size, construction and speed rating designations. See tyre sizes and speed ratings below.
C : Denotes type of tyre construction.
D : M&S denotes a tyre designed for mud and snow. Reinforced marking only where applicable.
E : Load and pressure marking requirement.



Tyre Sizing Systems

Over the years there has been many different methods used to size tyres. Many of these are still in use today, with the ISO Metric Sizing System the most widely used.

1. Numeric Sizing System
   This first system developed for tyre sizing was used until the late 1960s, but provided only the cross section width of the tyre and the rim diameter in inches. If the section width ended in zero (e.g., 7.00-14 or 7.50-14), the tyre had a common aspect ratio of about 92. For section widths not ending in zero (e.g., 8.25-15), the tyre was considered "low profile" with an aspect ratio of about 82.
   
   
   
2. Alphanumeric Sizing System
   In 1968, a new concept was introduced worldwide. The Alphanumeric sizing system is a load-based system where tyres are designated by their load-carrying capacity and aspect ratio. The first letter is the load and size relationship, with letters ranging from A to N. The lower the letter, the smaller the size and, of course, the lower the load-carrying capacity of the tyre.
   
   
   
3. P-Metric Sizing System
   To accommodate the smaller tyres used on compact cars, the P-Metric (Passenger Metric) system was created in 1976. The maximum inflation pressures of P-Metric tyres were raised for lower rolling resistance.
   
   
   
   
4. Metric Sizing System
   Because Europe primarily uses the metric system of measurement; the Metric sizing system was developed. It is essentially a conversion of the Numeric system. Section widths are notated in millimetres instead of inches. Originally, tyres not identified with an aspect ratio were assumed to be 82-series. When 60- and 70 series tyres appeared, the aspect ratio was added to the nomenclature, similar to the P-Metric system.
   
   
   
5. ISO Metric Sizing System
   The International Standards Organization (ISO) Metric system combines the Metric system with a service description. The service description provides the load index along with the speed rating symbol.
   
   
   
   
   
6. Millimetric Sizing System
   The Millimetric sizing system is similar to the Metric system except that the rim diameter is also represented in millimetres.
   
   
   
   
   
   
   
7. Light Truck Numeric System
   Similar to the Numeric system for cars, it lists the section width in inches, construction type, rim diameter in inches, plus the light truck designation.
   
   
   
   
   
   
8. Light Truck Metric System
   Similar to the P-Metric system, except the P is replaced with the LT light truck designation. Also, LT-Metric and P-Metric tyres differ in construction.
   
   
   
   
   
   
9. Light Truck High Flotation System
   Similar to the Numeric system for cars, it lists the section width in inches, construction type, rim diameter in inches, plus the light truck designation.

Other Markings

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.

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







Aspect Ratio (or sidewall height)

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.



Speed Ratings

All tyres carry a speed symbol in the form of a letter indicating the maximum speed for which the tyre is intended. This indicates the maximum speed that the tyre can sustain for a ten minute endurance without coming to pieces and destroying itself and the car it is on.

The table below shows which speed goes with each letter :

Speed Category Symbol Speed (km/h) Speed Category Symbol Speed (km/h) D 65 Q 160 E 70 R 170 F 80 S 180 G 90 T 190 J 100 U 200 K 110 H 210 L 120 V 240 M 130 W 270 N 140 Y 300 P 150 ZR * OVER 240

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 LI Kg LI Kg LI Kg LI Kg LI Kg 0 45 40 140 80 450 120 1400 160 4500 200 14000 240 45000 1 46.2 41 145 81 462 121 1450 161 4625 201 14500 241 46250 2 47.5 42 150 82 475 122 1500 162 4750 202 15000 242 47500 3 48.7 43 155 83 487 123 1550 163 4875 203 15500 243 48750 4 50 44 160 84 500 124 1600 164 5000 204 16000 244 50000 5 51.5 45 165 85 515 125 1650 165 5150 205 16500 245 51500 6 53 46 170 86 530 126 1700 166 5300 206 17000 246 53000 7 54.5 47 175 87 545 127 1750 167 5450 207 17500 247 54500 8 56 48 180 88 560 128 1800 168 5600 208 18000 248 56000 9 58 49 185 89 580 129 1850 169 5800 209 18500 249 58000 10 60 50 190 90 600 130 1900 170 6000 210 19000 250 60000 11 61.5 51 195 91 615 131 1950 171 6150 211 19500 251 61500 12 63 52 200 92 630 132 2000 172 6300 212 20000 252 63000 13 65 53 206 93 650 133 2060 173 6500 213 20600 253 65000 14 67 54 212 94 670 134 2120 174 6700 214 21200 254 67000 15 69 55 218 95 690 135 2180 175 6900 215 21800 255 69000 16 71 56 224 96 710 136 2240 176 7100 216 22400 256 71000 17 73 57 230 97 730 137 2300 177 7300 217 23000 257 73000 18 75 58 236 98 750 138 2360 178 7500 218 23600 258 75000 19 77.5 59 243 99 775 139 2430 179 7750 219 24300 259 77500 20 80 60 250 100 800 140 2500 180 8000 220 25000 260 80000 21 82.5 61 257 101 825 141 2575 181 8250 221 25750 261 82500 22 85 62 265 102 850 142 2650 182 8500 222 26500 262 85000 23 87.5 63 272 103 875 143 2725 183 8750 223 27250 263 87500 24 90 64 280 104 900 144 2800 184 9000 224 28000 264 90000 25 92.5 65 290 105 925 145 2900 185 9250 225 29000 265 92500 26 95 66 300 106 950 146 3000 186 9500 226 30000 266 95000 27 97.5 67 307 107 975 147 3075 187 9750 227 30750 267 97500 28 100 68 315 108 1000 148 3150 188 10000 228 31500 268 100000 29 103 69 325 109 1030 149 3250 189 10300 229 32500 269 103000 30 106 70 335 110 1060 150 3350 190 10600 230 33500 270 106000 31 109 71 345 111 1090 151 3450 191 10900 231 34500 271 109000 32 112 72 355 112 1120 152 3550 192 11200 232 35500 272 112000 33 115 73 365 113 1150 153 3650 193 11500 233 36500 273 115000 34 118 74 375 114 1180 154 3750 194 11800 234 37500 274 118000 35 121 75 387 115 1215 155 3875 195 12150 235 38750 275 121000 36 125 76 400 116 1250 156 4000 196 12500 236 40000 276 125000 37 128 77 412 117 1285 157 4125 197 12850 237 41250 277 128500 38 132 78 425 118 1320 158 4250 198 13200 238 42500 278 132000 39 136 79 437 119 1360 159 4375 199 13600 239 43750 279 136000