Decoding the Numbers on Your Tire Sidewall



Decoding the Numbers on Your Tire SidewallAt first glance, you look at your tire sidewall and think, “’Do I need a super-secret decoder ring to read this?” In addition to the brand and model name of the tire, there is a series of numbers and letters that at first do not seem important. However, these numbers and letters are helpful, especially when it’s time to replace your tires. Here’s a quick breakdown to help you decipher the code. ?Tire Size: ?Example: P185/75/R1482SP identifies your tire as a passenger tire. The P stands for P-metric. If your tire size starts with LT rather than a P then it identifies the tire as a light truck tire.185 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 it is fitted. 75 is the two-figure aspect ratio. This percentage compares the tire's section height with the section width. For example, the aspect ratio of 75 means that the tires section height is 75% of the tires section width. R indicates the construction used within the tires casing. R stands for radial construction. B means belted bias and D stands for diagonal bias construction. Most light duty tires are R construction.17 is the diameter of the wheel, which is most often measured in inches.RatingMaximum SpeedQ100 MPHS112 MPHT118 MPHU124 MPHH130 MPHV149 MPHW168 MPHY186 MPHZ>149 MPH82 The load index tells you how much weight the tire can support when properly inflated. Load indices range from 75 - 105 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. S is the speed ratings. It is represented by letters ranging from A to Z. Each letter coincides to the maximum speed a tire can sustain under its recommended load capacity. For instance, S is equivalent to a maximum speed of 112 mph. GSA does not advocate exceeding legal speed limits.?DOT Serial NumberThe DOT serial number located on the inside sidewall near the bead of the tire that seats up to the rim, certifies the tire manufacturer's compliance with the U.S. Department of Transportation (DOT) safety standards.?1617345698563500Starting with the year 2000, four numbers are used to identify the manufacture date, the?first two numbers identify the week and the last two identify the year of manufacture. DOT recommends that light duty tires older than 10 years should not be used.?Prior to 2000 three numbers were used for the manufacture date; the first two numbers identify the week and the last number identifies the year. A decade symbol (a triangle on its side) identifies tires manufactured in the 1990s. ................
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