To tell tire size, you need to read the sequence of numbers and letters printed on the tire's sidewall or find the information on your vehicle's door jamb or owner's manual. Here's how to interpret the common tire size format, for example: P225/70R16 91S.

How to Read Tire Size

• Tire Width (Section Width):
  The first number (e.g., 225) is the tire width in millimeters, measured from sidewall to sidewall

• Aspect Ratio:
  The number after the slash (e.g., 70) is the aspect ratio, which represents the height of the tire's sidewall as a percentage of the tire's width. An aspect ratio of 70 means the sidewall height is 70% of the width

• Construction Type:
  The letter following the aspect ratio (e.g., "R") indicates the tire's construction. "R" stands for radial construction, which is the most common. A "B" would indicate bias-ply construction

• Wheel Diameter (Rim Size):
  The number after the construction letter (e.g., 16) is the diameter of the wheel (rim) in inches that the tire fits

• Load Index:
  The number following the wheel diameter (e.g., 91) indicates the maximum load the tire can carry

• Speed Rating:
  The final letter (e.g., S) represents the maximum speed capability of the tire

Where to Find Your Tire Size

• On the sidewall of your current tires (best for matching existing tires)

• Inside the driver’s side door jamb or door frame

• In the vehicle’s owner’s manual or glove box

Summary Example: Tire Size P225/70R16 91S

Part| Meaning| Example Value| Explanation
---|---|---|---
Width| Tire width in millimeters| 225| 225 mm wide
Aspect Ratio| Sidewall height as % of width| 70| Sidewall height = 70% of 225 mm
Construction| Tire construction type| R| Radial tire
Wheel Diameter| Rim diameter in inches| 16| Fits a 16-inch rim
Load Index| Maximum load capacity| 91| Load capacity rating
Speed Rating| Maximum speed rating| S| Speed capability rating

This information helps ensure you select the correct tire size for your vehicle’s safety, performance, and handling