On the sidewall of every tire is an alphanumeric code that describes the dimensions of the tire. There is probably much more information on your tires than you realize. Typically all tires use letters and numbers to specify the load, speed, maximum inflation pressure, tire type, and tread width, among other qualities. 

P — The first letter classifies the tire by class. P stands for passenger car tire and LT stands for light truck tire.  

P225 — The number following the P or LT is the tire section width.  The Sidewall is measured from sidewall to sidewall in millimeters. A common width is 225

P225/55 — Following the section width is usually a slash (/) and then a two digit number such as 55 that represents the two-figure aspect ratio. This is the percentage of the section width. 

P225/55R — This letter indicates the construction used in the tire casing. R designates a radial tire, B stands for belted bias, and D stands for diagonal bias construction. 

P225/55R 19 — This number specifies the wheel diameter. The wheel diameter is the specific size in inches of the wheel that a tire fits. For example, this tire would fit a 19 inch wheel based on the number 19

P225/55R 19 89 — The number following the tire size is the load index. The load index indicates the amount of weight the tire can support. Check a load index chart to figure out what the load amount is based on that number. For example, an 89 load index can hold up to 1,279 lbs. 

P225/55R 1989— The letter following the load index indicates the speed rating. These letters range from A to Z. Check a speed rating chart to see what each letter represents. For example, a W means the tire can reach speeds up to 168 MPH under the recommended load capacity. 

DOT —The next set of letters and numbers usually begin with DOT which means that the tire is certified by the U.S. Department of Transportation tire safety standards. All tires for sale in the U.S. must meet the minimum DOT standards. 

DOT R8LN — The digits following DOT are typically the manufacturer’s plant identification code and size. 

DOTR8LN2AF — The next code is optional for manufacturers but stands for the tire type. It specifies the construction, tread pattern, and category of the tire. 

DOTR8LN2AF4616 —Following the tire type code is the week and year that the tire was produced. 46 stands for the 46th week in the year and 16 stands for the year, as in 2016. 

M+S — Some tires are labeled with a M+S which stands for mud and snow tires. 

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