Useful information for consumers is available from the code stamped on the sidewall of a car tire. Understanding the code and knowing how to read it can help determine general safety aspects, date of manufacture and numerous additional details. The format of the code is universal, so no matter the tire manufacturer, the three rows of the code will read the same.
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Determine the size, load index and speed rating of the tire by looking at the top row of numbers. This is important for replacement purposes. The code indicates the size and type of tire, the load index, or maximum weight the tire can carry, and maximum sustainable speed the tire can handle.
For example, the code P185/75R14 82s can be broken down to read: P: passenger tire 185: width in millimetres 75: ratio of sidewall height to width (number is a percentage) R: radial-ply construction 14: wheel diameter in inches 82: load index (an 82 load index correlates to 475 Kilogram) s: speed rating (an "s" speed rating correlates to 112mph)
Check the tread-wear rating, traction and temperature limits. The second row of numbers is a code developed by the Department of Transportation (DOT) to grade tire quality. They code signals the tread-wear and traction expectations for stopping on wet pavement, and temperature resistance scores.
For example, the code Tread-wear 360 Traction A Temperature A can be broken down to read:
Tread-wear 360: a rating of the tires durability as compared against a reference number of 100. A tread-wear rating of 360 means the tread on this tire should last 3.6 times longer than the tire tested by the DOT.
Traction A: measures a tyre's wet-stopping ability on a straight stretch of road. Ratings range from AA (the best) to C (the worst).
Temperature A: measures how well a tire is able to dissipate the effects of heat build-up that affect its ability to run at high speeds. Ratings vary from A (the best) to C (the worst).
Determine the maximum tire pressure. This number indicates the maximum safe air pressure the tire can handle. One thing to remember with this number is that most tire manufacturers recommend you not to inflate the tire to this maximum number. Manufacturers include recommendations with owner manual information.
For example, the code Max Pressure 40psi can be broken down to read no more than 18.1 Kilogram of air pressure per square inch.
Record the tyre's manufacture date. Any tire manufactured after the year 2000 must include the week and year of manufacture on the tire sidewall. DOT initials and identification numbers precede this information. For example, the code DOT U2LL LMLR 4208 can be broken down to read:
DOT U2LL LMLR: information for DOT use only
42: manufactured during the 42nd week of the year
08: manufactured during 2008
Tips and warnings
- When purchasing new tires, record the code from each and file with your owner manual.
- Check and adjust tire pressure in the morning before the tires have a chance to warm up.
- Never release air pressure from or add air to a hot tire.
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