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Understanding a Tire Size


Tire Type

"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.


Section Width

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.


Aspect Ratio

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.


Wheel Diameter

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.


Service Description

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 Load Index Weight Rating
75 852 lbs 100 1764 lbs
76 882 lbs 101 1819 lbs
77 908 lbs 102 1874 lbs
78 937 lbs 103 1929 lbs
79 963 lbs 104 1984 lbs
80 992 lbs 105 2039 lbs
81 1019 lbs 106 2094 lbs
82 1047 lbs 107 2149 lbs
83 1074 lbs 108 2205 lbs
84 1102 lbs 109 2271 lbs
85 1135 lbs 110 2337 lbs
86 1168 lbs 111 2403 lbs
87 1201 lbs 112 2469 lbs
88 1235 lbs 113 2535 lbs
89 1279 lbs 114 2601 lbs
90 1323 lbs 115 2679 lbs
91 1356 lbs 116 2756 lbs
92 1389 lbs 117 2833 lbs
93 1433 lbs 118 2910 lbs
94 1477 lbs 119 2998 lbs
95 1521 lbs 120 3086 lbs
96 1565 lbs 121 3197 lbs
97 1609 lbs 122 3307 lbs
98 1653 lbs 123 3417 lbs
99 1709 lbs 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.

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.



Locating my Tire Size

On the drivers door or door frame.

On the sidewall of a tire.


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