It is helpful to know what the numbers on you tires mean in case you cannot get to a tire technician; it also lets you price match and shop more effectively. In general, you should always try to stick to the same tire size as was manufactured with the vehicle.
The first three numbers represent the tire width, from the outside to the inside of the tire, in millimeters.
The next numbers will be separated by a forward slash (/). The two numbers following the forward slash are the aspect ratio of the tire, which is the height of the cross-section of the tire to its width. This number is usually between 35 and 90, but 60 is the average. These numbers will end in zero or five. The lower this number is, the smaller the tire.
Next will be one or two letters that describe the tire’s construction. This is usually an ‘R’ or radial for passenger vehicles. The letters ‘ZR’ indicate a performance radial for high speeds. The last two digits are the rim size in inches.
Other numbers and letters around represent load rating, speed rating, DOT symbol, TIN, UTQG, traction grades, and temperature grades.