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How to Read Tires: Decoding the Tire Sidewall Information

  • Wheels and Tires
  • Sara Sam
  • 5 minutes

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 On the rubbery surface lie the secret codes. It might look like a cryptic message waiting to be decoded, and it is certainly true to some extent. How do you read tires, and is it necessary? Here we look at how to read tires instead of staring at those perplexing symbols and numbers etched onto the tire sidewall the next time you see it.  

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How do I read a tire? 

Here is a checklist of what you must note while attempting to read a tire. 

  • Read the manufacturer and the tire name 
  • Note the service description or the size code. 
  • Find out the width and aspect ratio 
  • Understand the rim diameter 
  • Find the tire’s load index 

How to Read a Tire: Understanding Tire Size and Markings

To begin with, firstly, we look at what is written in big, bold font on the tires, which will probably catch your eye the moment you plan to learn how to read tires. If you are looking at something like this: P215/65R15 82 S, then it is the tire size code.  

Tire Type

“P” here stands for passenger vehicles, while other letters like “L.T.” are for light trucks. Similarly, “S.T.” is for special trailer tires.  

Width of the tire

The three-digit number which follows is the tire’s width in millimeters. In other words, it indicates the tire’s width from sidewall to sidewall.  

Aspect Ratio

The next two-digit number is the tire-aspect ratio which is the sidewall’s height as a percentage of the tread width. Here, the aspect ratio of 65 means the sidewall height is 65% of the tire’s width.  

Tire Construction

R stands for the most common type of tire construction: radial construction. However, if you see B instead of R, it is the cross-ply construction type.  

Diameter of the Wheel

The two-digit number, which is 15 here, denotes the diameter of the wheel in inches. 

Load Index Rating

When properly inflated, this rating specifies the maximum weight that a tire can support. Load index values range from 71, corresponding to a maximum load of 761 pounds, to 126, corresponding to a maximum weight of 3,748 pounds. 

However, load index values are based on a single tire, and the number of tires determines the total weight capacity of your vehicle’s tires on your vehicle and their separate load index ratings. 

Speed Rating

This rating indicates the highest sustained speed for which a given tire is designed. A speed rating of Q indicates a top speed of 99 mph, whereas a speed rating of Y indicates a top speed of 186 mph.  

  • Q-99mph 
  • R- 106 mph 
  • S- 112 mph 
  • T- 118mph 
  • U- 124mph 
  • H- 130 mph 
  • V- 149mph 
  • W*- 168mph 
  • Y*- 186 
  • Y**- above 186mph 

Want to know what tire size fits your car? Click here!

What is TIN Code?

The Tire Identification Number (TIN), known as the DOT code, is an alphanumeric character sequence molded into the tire’s sidewall. The U.S. Department of Transportation mandates this code. In addition, TIN enables the identification of the tire and its age. It is useful for identifying tires subject to a product recall or that have reached the end of their useful life due to age.  

Date of Manufacture  

The date-of-manufacture label tells how old the tire is. The letters D-O-T will be followed by batch and plant numbers. Consequently, there are four digits placed after these letters. The first two numbers represent the year, the week, and the year respectively. 

Maximum Inflation Capacity 

The maximum inflation capacity of a tire refers to the maximum air pressure that a tire can safely hold. However, it varies depending on the type of tire. The inner edge of the sidewall will carry the maximum pressure for the tires.  

Uniform Tire Quality Grading 

Commonly known as UTQG, it denotes the tolerances like treadwear rating, temperature range, and traction capabilities of a tire.  

Temperature and Traction Uniform Tire Quality Grading 

There is a recommended operating temperature for tires.  This is located after the treadwear rating. Temperature grade and traction grade each have a letter rating. “A.A.” is the highest rating for tires marketed in the United States, while “C” is the bare minimum.  

How to maintain your tires 

Reading the tires efficiently is the key to maintaining healthy tires. Here are some tips on how to maintain tires. 

  • Check your tire pressure regularly 
  • Inflate to the recommended PSI 
  • Have your tires rotated every 5,000 miles. 
  • Check the tread depth and any irregular wear. 
  • Replace worn-out tires 

Frequently Asked Questions 

How do you read tire specifications? 

To read a tire specification, you can look at the information printed on the tire’s sidewall. For instance, you’ll find the manufacturer’s name, service description, aspect ratio, construction, rim diameter, load index, and speed rating.  

What does R17 mean on a tire? 

The “R” in “R17” on a tire stands for “radial construction”. The “17” indicates the diameter of the wheel rim in inches. So, an R17 tire is a radial tire designed to fit a 17-inch wheel rim. 

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