How to Read Tire Size?
Tire sizes may look like a complicated combination of numbers and letters, but each part provides useful information about the tire’s dimensions and construction. Understanding these markings can make it easier to identify the correct tire size and compare options when shopping for replacement tires.
What Do Tire Size Numbers Mean?
For example, consider the tire size 235/65R18. Each part of this tire size provides specific information about the tire: 235 represents the tire width, 65 is the aspect ratio, R identifies radial construction, and 18 is the wheel diameter.
Tire Width - 235
The first number in the tire size represents the tire’s nominal section width in millimeters. In 235/65R18, the 235 indicates that the tire is approximately 235 millimeters wide from sidewall to sidewall.
Aspect Ratio - 65
The second number represents the tire’s aspect ratio. It describes the sidewall height as a percentage of the tire’s width. In 235/65R18, the sidewall height is 65% of the tire’s 235 mm width.
Tire Construction - R
The letter identifies the tire’s construction. In 235/65R18, R stands for radial construction, which is commonly used in modern passenger-vehicle tires.
Wheel Diameter - 18
The final number represents the diameter of the wheel that the tire is designed to fit. In 235/65R18, 18 means the tire is designed for an 18-inch wheel.
What About Load Index and Speed Rating?
You may see additional numbers and letters after the basic tire size. For example, in 235/65R18 106H, 106 is the load index and H is the speed rating.
The load index indicates the tire’s load-carrying capacity based on a standardized rating system, while the speed rating identifies the tire’s rated speed capability under specified conditions.
Learn more in our What Is Tire Load Index? guide and Tire Speed Ratings Explained guide.
Where Can You Find Your Vehicle's Tire Size?
Before purchasing replacement tires, check the tire specifications recommended for your vehicle. You can usually find this information on the Tire and Loading Information label, commonly located on the driver’s-side door edge or door jamb, or in your vehicle owner’s manual.
You can also read the size shown on your existing tire’s sidewall. However, tires currently installed on a used or modified vehicle may not always match the manufacturer’s original recommended size.
Find Tires for Your Vehicle
Once you know your tire size, Airless Tire Systems makes it easy to explore available tire options. Use Shop by Vehicle to search using your vehicle’s year, make, model, and trim, or use Shop Tires by Size if you already know the tire size you need.
Always verify the required tire specifications for your vehicle before purchasing replacement tires.