How to Read a Tire Sidewall: What All Those Numbers Mean
Decode tire sidewall markings to understand tire size, load rating, speed rating, and manufacturing date. Learn what all those numbers mean.
A tire sidewall is covered in numbers, letters, and codes that most car owners never understand. That string of characters — like '205/55R16 91V' — tells you everything about the tire's size, capacity, and performance rating. Knowing how to read a tire sidewall helps you buy the right tires, understand what your shop is recommending, and spot a tire problem before it becomes dangerous.
Tire Size: Understanding the Code
A tire size marking like '205/55R16 91V' breaks down as follows: 205 is the tire width in millimeters (the distance from sidewall to sidewall). 55 is the aspect ratio as a percentage (sidewall height is 55% of the width). R means radial construction (the standard for all modern car tires). 16 is the wheel diameter in inches (the rim it fits). 91 is the load index (what weight the tire can carry). V is the speed rating (safe maximum sustained speed).
Load Index and Speed Rating
Load index tells you the maximum weight each tire can support. A load index of 91 means that tire can safely carry 1,356 pounds. For a car with four tires, multiply by four to get total capacity. Speed ratings range from L (75 mph) to H (130 mph) to Z (over 149 mph). Never install a tire with a lower speed rating than the vehicle's top speed. Match the load and speed ratings to your vehicle's requirements — found on a placard inside the driver's door or in the owner's manual.
Other Sidewall Markings
DOT code: Unique identifier for traceability. The last four digits indicate manufacture date (week and year). A code ending in '2614' means week 26 of 2014. Treadwear rating: A number like 500 or 800 indicating expected tire life. Higher numbers last longer. UTQGS rating: Treadwear, traction, and temperature ratings (A, B, or C). M+S or All-Season marking: Indicates all-season or mud/snow capability. Directional arrow: Some tires have a preferred rotation direction for wet traction.
Age and Replacement
Tires older than 10 years should be replaced regardless of tread depth because rubber degrades over time. Check the DOT code on the sidewall to determine the manufacturing date. Even if a tire looks fine, rubber oxidizes and loses flexibility with age, which impacts safety and performance.
Why This Matters to Your Shop
Understanding tire codes helps you communicate with customers about what you're recommending and why. It also helps you catch customer mistakes — like installing a tire with inadequate load rating on a heavier vehicle. Document tire specifications in work notes so you and the customer have a record.
When you install new tires, <a href='/features'>Mechanics</a> allows you to store tire inventory by size and specification, track installation dates for warranty purposes, and set reminders for tire rotation and replacement. This ensures every customer's tire history is documented and available the next time they need service.
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