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Understanding a Tire Size
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Tire Type |
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"P" - (Passenger) - Indicates that the tire was engineered to meet certain load capacity requirements set by United States regulations. Typically, these types of tires are used on passenger cars, vans, mid-sized SUVs / trucks and some full-sized SUVs / Trucks.
"LT" - (Light Truck) - These types of tires are engineered to meet much heavier load capacity requirements set by United States regulations and can be rated for both Single Wheel and Duel Wheel appications. They are used on most full-sized SUVs and full-sized trucks. These tires have lower speed ratings than passenger type tires.
NO LETTER - (European) - While the measurements of the tire itself are the same as a tire that is engineered for United States regulations, these tires are designed to meet European standards. European standards have different load capacity specifications and vary when compared to a tire designed to meet United States regulations.
"ST" - (Special Trailer) - These tires are engineered to be used for trailer applications. Depending on the tire size, the load range indicates the maximum load capacity the tire is engineered to handle at certain inflation pressures.
"T" - (Temporary Spare) - Also, referred to as "Donut Tire". These tires are used for temporary use only and are speed limited, typically to 80kph (50mph).
The example tire size we used indicates it is a "P" rated tire.
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Section Width |
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This is the width of the tire measured in millimeters(mm) from one sidewall of the tire to the other. The actual measurement can vary if the tire is mounted on a rim with a depth that is larger or smaller than what the tire was engineered to be installed on.
The example tire size we used has a section width of 225mm.
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Aspect Ratio |
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This is the height of the tire from the bead to the tread of the tire. It is a percentage of the section width and can also vary depending on the rim depth.
The example tire size we used has a 55 percent aspect ratio.
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Wheel Diameter |
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This is the diameter of the rim (or wheel) that the tire was engineered to be installed on. It is used to measure the tire's inside diameter. The tire must be mounted to a rim that matches this size.
The example tire size we used has a 17 inch wheel diameter.
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Service Description |
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LOAD INDEX - The numbered portion of the tire's service description. This indicates the load capacity of the tire when properly inflated.
| Load Index |
Weight Rating |
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Load Index |
Weight Rating |
| 75 |
852 lbs |
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100 |
1764 lbs |
| 76 |
882 lbs |
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101 |
1819 lbs |
| 77 |
908 lbs |
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102 |
1874 lbs |
| 78 |
937 lbs |
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103 |
1929 lbs |
| 79 |
963 lbs |
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104 |
1984 lbs |
| 80 |
992 lbs |
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105 |
2039 lbs |
| 81 |
1019 lbs |
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106 |
2094 lbs |
| 82 |
1047 lbs |
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107 |
2149 lbs |
| 83 |
1074 lbs |
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108 |
2205 lbs |
| 84 |
1102 lbs |
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109 |
2271 lbs |
| 85 |
1135 lbs |
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110 |
2337 lbs |
| 86 |
1168 lbs |
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111 |
2403 lbs |
| 87 |
1201 lbs |
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112 |
2469 lbs |
| 88 |
1235 lbs |
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113 |
2535 lbs |
| 89 |
1279 lbs |
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114 |
2601 lbs |
| 90 |
1323 lbs |
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115 |
2679 lbs |
| 91 |
1356 lbs |
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116 |
2756 lbs |
| 92 |
1389 lbs |
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117 |
2833 lbs |
| 93 |
1433 lbs |
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118 |
2910 lbs |
| 94 |
1477 lbs |
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119 |
2998 lbs |
| 95 |
1521 lbs |
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120 |
3086 lbs |
| 96 |
1565 lbs |
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121 |
3197 lbs |
| 97 |
1609 lbs |
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122 |
3307 lbs |
| 98 |
1653 lbs |
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123 |
3417 lbs |
| 99 |
1709 lbs |
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124 |
3527 lbs |
A tire that was designed to meet United States regulations would have a load index that correspond to a measurement in pounds. A tire that was designed to meet European standards would correspond to a measurement in kilograms but in some cases, pounds as well.
Some Light Truck(LT) tires have a load index consisting of two numbers seperated by a forward slash. The first number indicates the load index if the tire was used on a Single Wheel application and the second number indicates the load index if the tire was used on a Duel Wheel application.
You can install tires with higher load index(s) than what the vehicle requires but you should not install tires with lower load index(s) as that will affect load capacity.
The example tire size we used has a load index of 97.
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SPEED RATING - The lettered portion of the tire's service description. This indicates the maximum speed rating of the tire. Though the attribute uses the alphabet, the rating does not follow this order.
| Index |
Speed Rating |
| L |
120 kph (75 mph) |
| M |
130 kph (81 mph) |
| N |
140 kph (87 mph) |
| P |
150 kph (93 mph) |
| Q |
160 kph (99 mph) |
| R |
170 kph (106 mph) |
| S |
180 kph (112 mph) |
| T |
190 kph (118 mph) |
| U |
200 kph (124 mph) |
| H |
210 kph (130 mph) |
| V |
240 kph (149 mph) |
| W |
270 kph (168 mph) |
| Y |
300 kph (186 mph) |
The higher the speed rating, the better handling, conform and performance at higher speeds. Unfortunately, tread life decreases the higher the speed rating. Light Truck(LT) tires typically have lower speed ratings than Passenger(P) tires.
You can install tires with higher speed ratings than what the vehicle requires but you should not install tires with lower speed ratings as that will affect performance.
The example tire size we used has a speed rating of S.
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Locating my Tire Size
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On the drivers door or door frame.
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On the sidewall of a tire.
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