Understanding the information provided on your tire sidewall can be overwhelming. The combination of letters, numbers, and symbols may seem like a secret code. However, reading a tire size becomes much simpler with some knowledge. This guide will break down the components of tire size and help you decipher its meaning.
Tire Width:
The first number in a tire size represents the tire’s width in millimeters. For example, if the tire size reads “225/50R17,” the tire’s width is 225 millimeters.
Aspect Ratio:
After the forward slash, you’ll find a two-digit number representing the aspect ratio or tire profile. This number indicates the height of the tire’s sidewall as a percentage of its width. In our example (225/50R17), the aspect ratio is 50, meaning the sidewall height is 50% of the tire’s width.
Construction Type:
The letter following the aspect ratio denotes the construction type of the tire. The most common letter is “R,” which stands for radial construction. Radial tires are the standard type used in modern vehicles. Other letters you may encounter include “B” for bias-ply construction or “D” for diagonal construction, although these are less common today.
Rim Diameter:
The next number indicates the diameter of the wheel or rim in inches. Matching your tire size to the rim diameter ensures proper fitment and performance.
Load Index and Speed Rating:
Following the rim diameter, you may find two additional numbers or symbols. The load index represents the maximum weight capacity the tire can support. It is a numerical value ranging from 70 to 126, with each number corresponding to a specific weight capacity. The speed rating symbol represents the maximum speed the tire can handle safely. Common speed ratings include “H” for up to 130 mph, “V” for up to 149 mph, and “W” for up to 168 mph.
For the recommended tire size, consult the owner’s manual or the placard on the driver’s side door jamb. While you may have some flexibility in tire selection, it is best to stick to the manufacturer’s recommendations for optimal performance and safety.
