How to read tire sizes: all numbers explained
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Have you ever wondered what all those numbers and letters on your tire's sidewall mean? In tire size each of those symbols (letters or numbers) have a specific meaning such as size, type and performance of the tire. There are two types of tire measurements: P-metric and flotation.
Below you will see an example of P- metric measurement with the basic information you will find on your vehicle's tire and need to know in order to purchase a brand new tire for your car when the time comes. Read tire measurements is easier than you think and really helpful when it is time to use.
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| Tire size explained |
Initial letters or tire type
The tire sizes can start with the letters P, LT, ST or T.
P 205 / 50 / R 17 98 H
P - passenger tire size
P means passenger vehicle. According to the American Automobile Labeling Act (AAA) from NHTSA (National Highway Traffic Safety Administration), passenger vehicles are those "designed to carry no more than 12 persons with a gross vehicle weight rating not greater than 8,500 pounds." such as sedans and minivans for example.
LT - Light Truck tire size
You might also see tire specifications that start with LT. It stands for light trucks and are tires suitable for trucks that carry extra heavy loads or tow a trailer. This kind of tire has an extra coat of material to protect the tire from being damaged.
ST- Special Trailer tire size
ST stands for Special Trailer, and as the name indicates itself, they are made for trailers.
T - Temporary tire size
The ones that start with T are the temporary or spare tires. Those are as the name says itself, for temporary use only.
Wheel / rim width - (millimeters)
P 205 / 50 / R 17 98 H
The 3 numbers after the letters (205) indicate the width of the tire from one sidewall to another, measured in millimeters.
Aspect ratio
P 205 / 50 / R 17 98 H
The two numbers after the slash (50) indicate the aspect ratio. It is how you find the section height measurement of your tire or your tire's sidewall height. It is the size of the sidewall compared to the tire width. For example, in a tire specifications 265/50R19, the ration 50 means that the height is 50% of 265.
R - radial
P 205 / 50 / R 17 98 H
It specifies the internal construction of the tire as radial. Each layer runs radially across the tire, perpendicular to the direction of rotation.
In some cases, you can also see D or B or even "-" that means diagonal or bias ply construction.
You might also find tires as ZR and that indicates the tire has a speed rating higher than V.
The wheel size - diameter
The two numbers after R (17) indicate the wheel size in inches.
Load Index or capacity
The following 2 or 3 numbers (98) ranging from 0 to 279, specify the load index. The name seems complicated, but it just means how much weight the tire can support.
For example, a tire with load index 98 supports up to 1,653 lbs. when inflated. Just multiply it by four to find the maximum weight your vehicle can have.
TIRE LOAD
INDEX CAPACITY Load Index Load (lbs) Load Index Load (lbs) Load Index Load (lbs) 0 99 50 419 100 1764 1 102 51 430 101 1819 2 105 52 441 102 1874 3 107 53 454 103 1929 4 110 54 467 104 1984 5 114 55 481 105 2039 6 117 56 494 106 2094 7 120 57 507 107 2149 8 123 58 520 108 2205 9 128 59 536 109 2271 10 132 60 551 110 2337 11 136 61 567 111 2403 12 139 62 584 112 2469 13 143 63 600 113 2535 14 148 64 617 114 2601 15 152 65 639 115 2679 16 157 66 639 116 2756 17 161 67 677 117 2833 18 165 68 694 118 2910 19 171 69 716 119 2998 20 176 70 739 120 3086 21 182 71 761 121 3197 22 187 72 783 122 3307 23 193 73 805 123 3417 24 198 74 827 124 3527 25 204 75 852 125 3638 26 209 76 882 126 3748 27 215 77 908 127 3858 28 220 78 937 128 3968 29 227 79 963 129 4079 30 234 80 992 130 4189 31 240 81 1019 131 4289 32 247 82 1047 132 4409 33 254 83 1074 133 4541 34 260 84 1102 134 4674 35 267 85 1135 135 4806 36 276 86 1168 136 4938 37 282 87 1201 137 5071 38 291 88 1235 138 5203 39 300 89 1279 139 5357 40 309 90 1323 140 5512 41 320 91 1356 141 5677 42 331 92 1389 142 5842 43 342 93 1433 143 6008 44 353 94 1477 144 6173 45 364 95 1521 145 6393 46 375 96 1565 146 6614 47 386 97 1609 147 6779 48 397 98 1653 148 6844 49 408 99 1709 149 7165 150 7385
Speed rating
It specifies the highest speed the tire was designed for and up to what is operates safely. It is also to be aware that, it is not recommended to have tires with different speed rates on the same vehicle. It can limit your vehicle`s limit capability.
You can check the maximum speed for your tire on the table below.
Speed Rating Maximum speed (mph) L 75 mph M 81 mph N 87 mph P 93 mph Q 99 mph R 106 mph S 112 mph T 118 mph U 124 mph H 130 mph V 149 mph Z 149+ mph W 168 mph Y 186 mph (Y) 186+ mph
Please keep in mind that the maximum speed of your tire is not the maximum you can drive at. If your vehicle has different speed ratings the lowest speed rating is the one that must be considered. But make sure to follow the speed limit!
Please let me know if this content has helped you! Do you still have questions? Let me know in the comments.
Best,
Vivian Santos
Car Safe Car Team
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