Essential for North American Living: Complete Guide to Tire Sidewall Code Meanings

Every time you go to Costco to get your tires changed, do you feel confused when you see that string of characters on the side that looks like a "Da Vinci Code"? These codes are actually the "ID card" of your tires, and they matter for driving safety. (Note: The following information is based on general industry standards as of 2026.)

🔹 Breaking Down the Key Parameters: Using 225/45 R17 91W as an Example

Code	What It Means	Expert Advice
225	Tire width (225mm)	Affects grip and fuel economy
45	Aspect Ratio	Sidewall height is 45% of the width
R	Radial construction	Mainstream structure for modern passenger cars
17	Wheel diameter (17 inches)	Must match your rim size
91	Load Index (Max 615kg)	Maximum weight per tire; never go lower than recommended
W	Speed Rating (Max 270km/h)	Indicates the maximum speed the tire can handle

🔹 DOT Manufacturing Date: Key to Avoiding Issues and Staying Safe

Look for the DOT mark and focus on the last 4 digits. For example, 2424 means the tire was manufactured in the 24th week of 2024. When buying new tires, be cautious if you find stock that's over 3 years old. When buying a used car, even if the tread looks deep, it's recommended to replace tires that are over 6 years old.

🔹 Common Community Q&A

▫️ Which is better, 106H or 104V?

 

The number indicates load capacity, and the letter indicates speed rating. As long as the physical dimensions are the same, it's recommended to choose a model with specs that are no lower than the original factory configuration.

▫️ Can I just swap tires freely as long as the physical dimensions match?

 

Not recommended. Different models have different load indexes and structural characteristics. Blindly swapping tires can affect your vehicle's handling stability and insurance claims.