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 You can learn a lot about your tires from reading the sidewalls. The alphanumeric code may seem like hieroglyphics at first, but once you know what each section stands for you'll be a smarter tire shopper.
Tire Size
Example P205/55R16 91W
P identifies the tire as a passenger tire. If the tire size starts with LT rather than P the tire is meant for use on a light truck.
205 identifies the tire section width, which is the measurement of the tire from sidewall to sidewall in millimeters. This measurement varies depending on the rim to which the tire is fitted. (There are 25.4 millimeters per 1 inch.)
55 is the two-figure aspect ratio. This percentage compares the tire's section height with the tire's section width. For example, this aspect ratio of 55 means that the tire's section height is 55% of the tire's section width.
R indicates the construction used within the tire's casing. R stands for radial construction. B means belted bias, and D stands for diagonal bias construction.
16 is the last dimension listed in the size and represents the diameter of the wheel rim, which is most often measured in inches.
Load Index and Speed Rating
91 - The load index and speed rating, or service description, are the numbers that follow the tire size.
The load index tells you how much weight the tire can support when properly inflated. Load indices range from 74 to 150 for passenger tires with each numeric value corresponding to a certain carrying capacity. The carrying capacity for each value can be found on a load index chart. On each U.S. passenger car tire, the load limit is listed in pounds. On European tires the load limit is listed in kilograms and sometimes pounds.
W - Speed ratings are represented by letters ranging from A to Z. Each letter coincides with the maximum speed a tire can sustain under its recommended load capacity. For instance, S is equivalent to a max speed of 112 mph. Even though a tire can perform at this speed, we do not advocate exceeding legal speed limits.
| Speed Symbol |
Speed (km/h) |
Speed (mph) |
| A1 |
5 |
3 |
| A2 |
10 |
6 |
A3
|
15 |
9 |
| A4 |
20 |
12 |
| A5 |
25 |
16 |
| A6 |
30 |
19 |
| A7 |
35 |
22 |
| A8 |
40 |
25 |
| B |
50 |
31 |
| C |
60 |
37 |
| D |
65 |
40 |
| E |
70 |
43 |
| F |
80 |
50 |
| G |
90 |
56 |
| J |
100 |
62 |
| K |
110 |
68 |
| L |
120 |
75 |
| M |
130 |
81 |
| N |
140 |
87 |
| P |
150 |
94 |
| Q |
160 |
100 |
| R |
170 |
106 |
| S |
180 |
112 |
| T |
190 |
118 |
| U |
200 |
124 |
| H |
210 |
130 |
| V |
240 |
149 |
| W |
270 |
168 |
| Y |
300 |
186 |
| (Y) |
Above 300 |
Above 18 |
DOT Serial Number
The "DOT" symbol and serial number certify that the tire's manufacturer has complied with the U.S. Department of Transportation's tire safety standards. Here's a description of the serial number:
Starting with the year 2010, four numbers are used for the Date of Manufacture. The first two numbers identify the week of the year (01 thru 52), and the last two numbers identify the year the tire was made.
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