A tire's aspect ratio is its height to width in percentage. A tire with 205 mm width and 55 mm sidewall height has a 55% aspect ratio. Aspect ratio impacts tire diameter. The first number in a tire size is the width in millimeters, and the second represents the aspect ratio. Tire size can be defined as a collection of numbers and letters that describe tire type, width, sidewall height, and wheel diameter — alongside other information. An example of a common tire size is as follows: P225/65R17. The tire size for your vehicle and wheels can be found in two places: The sidewall of your tire. Diameter : 35 The Diameter of this tire size is 35 inches. The first number in a high flotation tire size is the overall diameter of the tire. Section Width : 12.50 The width of this tire size is 12.5 inches. The second number in a high flotation tire size is the width of the tire in inches. Tire Construction : R The number 185 is the tire's width in millimeters, from one sidewall to the other. The number 60 after the forward slash character means the tire's height from rim to tread is 60 percent of its width, which again is 185 millimeters. R14 means the tire is meant to fit on a 14-in. diameter wheel. Tire Size Meanings 1. Tire Type. Most car tires have the letter "P" at the front of the tire size. This letter signifies that it is a 2. Tire Width. The tire is measured by its width. This measurement is given in millimeters, based on how much room there 3. Aspect Ratio. After the slash mark, Tire Size Guide: How to Read Tire Numbers and Letters Tire Class. The tire class is indicated at the beginning of the tire code. Typically, you'll see the letters P, LT, or Tire Width. The three-digit number following the tire class is the tire width. The width is the distance of the tire The set of numbers straight after the tyre width refers to the thickness of the tyre wall (or aspect ratio), which is a percentage of the width. So, in this case, 55 would have a height equal to 55% of the tyre's width. This number is often referred to as the tyre profile. Tyre construction It is indicated by a letter of the alphabet, which refers to a table that is common to all manufacturers. Each letter corresponds to a certain maximum speed. It starts from letter "A", the only one which is broken down with numbers (A1, A2, A3, etc.) and which allows speeds of between 5 to 40 km/h. J - On some wheels, the letter 'J' might appear next to the wheel width, such as 16x7J. The letter J lets you know the shape of the wheels, and how the tire beads align with the wheels. J is commonly used for most passenger vehicles. Specialized vehicles may use other markings such as JJ, K, JK, B, P, A, D, S, T, or W. A typical tire size might read: P 205/65 R 15 92 H Here's what that means. P — This denotes a Passenger or P-metric tire built to U.S. standards. Here are other possible prefixes: LT is for a light truck. ST is for a special trailer. T is for temporary, usually indicating a spare tire. European-standard tires won't have a prefix letter at all. j5WVqUQ.