Maintenance
How to Read Tire Sidewall Codes
Published by AutoAnvil Editorial Team on
Size, load index, speed rating, and date codes decoded so you buy the right rubber and retire old tires on time.
Why the Sidewall Matters
The sidewall is the tire’s specification label. Misreading size or load rating can hurt handling, speedometer accuracy, and safety. Date codes tell you when a tire was manufactured — age matters even when tread looks deep.
Size String Basics
A common P-metric example looks like P225/45R17. Section width is in millimeters, aspect ratio is sidewall height as a percent of width, R means radial, and 17 is rim diameter in inches. LT metrics and flotation sizes use related but not identical conventions — match what your vehicle requires.
Load Index and Speed Rating
After the size you will see a service description such as 94W. The number is a load index; the letter is a speed rating. Do not downsize load capacity below the vehicle placard. Speed ratings are not a dare — they indicate tested capability under controlled conditions.
DOT Date Code
The last four digits of the DOT code are week and year of manufacture (for example 2325 means week 23 of 2025). Tires age via oxidation and environmental exposure. Many shops recommend replacement around six to ten years depending on use, storage, and manufacturer guidance — inspect annually.
Other Marks Worth Noticing
M+S and mountain-snowflake symbols relate to mud/snow and severe-snow capability. Run-flat markings, extra-load XL, and OEM proprietary codes can restrict replacements. When in doubt, use the door-jamb placard and a reputable tire retailer’s fitment tools.
Buying Without Getting Upsold Blindly
Prioritize the correct size and load rating, then choose a tire category that matches your climate and driving (all-season, summer performance, dedicated winter). Quietness and treadwear warranties are secondary to wet braking and fitment.
Frequently Asked Questions
Can I mix tire sizes?
Generally no on the same axle, and many AWD systems are sensitive to circumference mismatch. Follow the manufacturer.
Is deeper tread always newer?
No. An old tire can have unused tread. Check the date code.