Reading the writing on your tire's sidewall to be safe

                    Those numbers and letter etched into the sidewall of your tire are not a Bridgetone engineer's absent-minded doodles that made it past a slumbering quality assurance inspector.  In fact, the hieroglyphics stand as the operator's manual of the rubber that meets the road, with each sequence telling you a bit more about the tires performance.
                    Thanks to the information researched by Karl Brauer, Edmunds.com's editor-in-chief, you can know all you need to about the tires on your car.
                    Two concentric circles of type provide not only the manufacturer's name, but a litany of information about the tire itself.  The larger, outer circle of symbols provides the following information.
Tire Width
         On cars, the three-digit number indicates the tire's section width in millimeters from sidewall edge to sidewall edge when measured up and over the tire's tread.  Obviously, the larger the number, the wider the tire.  This number is followed by a slash (/) on the other side of which more symbols reveal more information.
Aspect Ratio
         The number immediately following the slash is the tire's aspect ratio, or the percentage of its section height compared to its section width.  A lower number, below 55, can mean a short sidewall, which will afford better steering response and overall handling.  The larger the number, the taller the tire and the more compromised the handling, but the better the fuel efficiency.
Internal Construction
          It's possible to actually find a "B" (for bias-ply construction) following the aspect ratio number, but more likely an "R" (for radial construction) will be found.  Radial consruction has been the industry standard in passenger-car tires for nearly 30 years.
Rim Diameter
         While the width is indicated in millimeters, the rim diameter is recorded in inches.  This is an important number to know if you are planning to upgrade your wheel size.  If your rim diameter changes, your tires need to be changed, too.


Load Index
         The last number in the outer sequence is the load index which measures how much weight each tire has been engineered to support.  The higher the number can be looked up on a load carrying capacity chart (www.discounttire.com/dtcs/infoLoadindex.dos).  For example, finding 85 on the chart will tell you that each tire can support up to 1,135 pounds.  When needing to replace your old tires, buy new ones with the same or greater load index.
Speed Rating
         The terminating letter at the end of the sequence is for speed rating, the measurement of the speed at which the tire is designed to run for extended periods.  For example, a "U" speed rating tells you that the tire is safe being run for extended duration at speeds up to 124 mph.
         The complete list is :
                         S = 112 mph
                         T = 118 mph
                         U = 124 mph
                         H = 130 mph
                         V = 149 mph
                         Z = Over149 mph
                         W = 168 mph
                         Y = 186 mph
         The inner smaller circle of symbols indicates the following information.
Dot Code
         The DOT code is used by the government to track tire production for recall purposes.  A four-digit number at the end of the code provides the week and the year the tire was made.  For example, 2211 would be the 22nd week of 2011.  Moreover, with manufacturing date known, you can make a wise decision about replacement.  Tires more than six years old should be replaced, according to tire experts.
Maximum Air Pressure
          This is not the recommended tire pressure but the maximum amount of air you can put in a tire before it is damaged.  Maximum pounds per square inch is found on your door jamb.
Traction Rating
          This rating reflects a tire's traction when tested for straight-line braking on a wet surface.  For this rating, AA signifies the best traction performance and C indicates the worst, with intermediary levels at A and B.
Temperature Rating
          Indicated from best to worse as A, B and C, this rating refers to the tire's ability to withstand heat under high speeds.
Treadwear Rating
         In small print you may find the word "TREADWEAR" on the sidewall with a number following it. The number indicates a tire treads durability as tested against an industry standard, whose reference point is 100.  Dr. Watson would be proud of your powers of detection regarding divining vital information about your vehicle's tires from those bewildering sidewall codes.  You and your family, however, will be safer.