How to Read a Tire Sidewall

Every tire has a story to tell, printed right on its sidewall. Understanding these markings is essential for choosing the right replacements, maintaining safety, and knowing when it's time for a change. This guide breaks down every code you'll find on your tires.

Decoding Tire Size Notation

A typical tire size looks like this: P225/65R17 102H. Here is what each part means:

• Service Type (P): "P" stands for Passenger car. "LT" stands for Light Truck. No letter often indicates a Euro-metric size.
• Section Width (225): The width of the tire in millimeters from sidewall to sidewall.
• Aspect Ratio (65): The height of the tire's cross-section as a percentage of its width. In this case, the height is 65% of 225mm.
• Construction (R): "R" stands for Radial, which is the standard construction for modern passenger tires.
• Wheel Diameter (17): The diameter of the wheel (rim) in inches that the tire is designed to fit.

Load Index and Speed Rating

The last part of the size string, 102H, provides critical performance data:

• Load Index (102): A numerical code indicating the maximum weight the tire can support when properly inflated. A 102 rating corresponds to 1,874 lbs.
• Speed Rating (H): A letter indicating the maximum speed the tire can safely maintain. "H" corresponds to 130 mph. Common ratings include T (118 mph), V (149 mph), and W (168 mph).

The DOT Date Code

Tires age even if they aren't driven. The DOT (Department of Transportation) code tells you where and when the tire was made. Look for a sequence starting with "DOT". The last four digits are the most important:

• The first two digits represent the week of manufacture.
• The last two digits represent the year.

For example, 3422 means the tire was made in the 34th week of 2022. Most manufacturers recommend replacing tires after 6 to 10 years, regardless of tread wear.

UTQG Ratings: Treadwear, Traction, and Temperature

The Uniform Tire Quality Grading (UTQG) system provides comparative info:

• Treadwear: A number like 400 or 600. The higher the number, the longer the tread should last compared to a standard reference tire.
• Traction: Rated AA, A, B, or C. This measures the tire's ability to stop on wet pavement. AA is the highest.
• Temperature: Rated A, B, or C. This measures the tire's resistance to heat generation at high speeds. A is the highest.

Run-Flat Indicators

Some tires are designed to be driven for a short distance after a puncture. Look for markings like RFT (Run-Flat Technology), SSR (Self-Supporting Run-flat), or ZP (Zero Pressure). These tires have reinforced sidewalls to support the vehicle's weight without air.

Tire Types and Seasonal Markings

• M+S: Stands for Mud and Snow. Found on all-season tires.
• 3PMSF (Mountain Snowflake): A symbol of a snowflake inside a mountain. This indicates the tire meets specific snow traction performance requirements and is suitable for severe winter conditions.

Tire Pressure (PSI)

The "Max Press" listed on the sidewall is the maximum pressure the tire can hold, not the recommended pressure for your car. Always follow the pressure listed on the sticker inside your driver's side door jamb or in your owner's manual.

The Penny Test for Tread Depth

To check if your tires are worn out, insert a penny into a tread groove with Lincoln's head upside down. If you can see the top of Lincoln's head, your tread is below 2/32 of an inch and you need new tires immediately.

Alignment and Rotation Schedules

• Tire Rotation: Rotate tires every 5,000–7,500 miles to promote even wear.
• Wheel Alignment: Get an alignment check every year or if you notice your car pulling to one side or uneven tread wear.
• Balancing: Have tires balanced whenever they are mounted to a wheel or if you feel vibrations at highway speeds.

Frequently Asked Questions