First up are the markings on tire size. (Example: P195/60R15 87Q)

P stands for Passenger. You may find other abbreviations in place of P, for example:

LT for Light Truck and T for Temporary/Spare tire.

195 stands for the width of the tire in millimeters between the sidewalls.

60 stands for the aspect ratio. The aspect ratio is the ratio of tire width to sidewall height.

R indicates that the tire has a radial construction. You may find other abbreviations in place of R, for example, B which indicates Belted Bias or D that represents Diagonal Bias15 next to R indicates the rim or the wheel diameter in inches.

87 represents load index.

Finally Q (or at times H, S, T, U, V, W, Y, etc.) represents the speed rating. Under ideal situations, the top speed attainable by the tire is indicated by the speed rating.

Next we will read the UTQG Ratings.

Uniform Tire Quality Grading, mandated by the Federal Government rates the tire's tread life. It examines the traction, tread wear, resistance temperature, etc. before deciding on a value. Located opposite the tire size marking that we examined a while back, the UTQG Rating will have separate readings/ratings for temperature, traction and treadwear.

The general treadwear grade is standardized at 100. So if you see 200 as treadwear rating then it indicates that the tire will wear twice as well as a tire with a 100 treadwear.

Traction grades are generally indicated by letters: AA to C. AA is the highest grade while C indicates that on wet asphalt and concrete, the braking power of the tire is poor.

The tire's resistance to heat and dispel heat is indicated by Temperature grades. Temperature grades are also indicated by alphabets. A indicates that the tire can resist heat well, B indicates that it cannot resist heat as good as a tire with A rating and C barely passes the minimum standards for safety. Tire temperature grades are also affected by heavy load or improper tire pressure.

All these grades are however measured in controlled environment when the tires are tested. Weather conditions, driving habits, road conditions will affect the performance of the tires in real life.

Finally let's learn how to do the DOT reading:

Department of Transportation abbreviated as DOT certifies whether the tire is complies with the DOT standards for safety that are applicable to this vehicle. Next to the DOT certification is the serial number that indicates the date and place of the production of the tire.

Other than the three major categories of numbers and ratings, you will get information on the ideal tire pressure, the composition of the tire and the tire type also indicated on the sidewall. Once you are able to crack the sidewall code, you are good to buy tires for your vehicle on your own.