How to Read Tire Size

Tire Width

Tire width is a three-digit number that follows the tire class. This is the measurement from one sidewall to another in millimeters. For example, the marking of "P245/" means you have a passenger vehicle with a tire width of 245 millimeters. 

Aspect Ratio

Past the tire width and slash mark will be a two-digit number called the aspect ratio. This number is the ratio of the height of the tire's cross-section to its width. 

Construction

Next comes a letter that indicates the construction of the tire. Radial tires are the most common type of tire, and they're noted by the letter "R." These tires are built with layers of fabric with cords that run at right angles to the circumference of the tire. This type of construction increases tire performance and strength. 

Wheel Diameter

The wheel diameter comes next and is represented by a two-digit number which specifies the measurement in inches of the wheel a tire will fit. For example, a "20" means your tire will fit a 20-inch wheel. 

Load Index

The load index number represents the maximum load the tire can carry when properly inflated and comes after the wheel diameter. For any vehicle, it's important to have a tire load index that meets or exceeds the specifications set by your vehicle's manufacturer.

Speed Rating

The letter following the load index is indicative of the speed rating of the vehicle. Speed ratings start with "Q" rated tires with a top speed of 99 mph, but ratings can extend to "(Y)" ratings -- which means tires are able to handle over 186 mph. Regardless of what your tires are rated for,  you'll need to follow posted speed limits as well as take weather and road conditions into account. 

More Tire Codes

Tire codes are for more than just sizing -- some offer additional information related to safety standards and where your tire is created. Other tire markings you may notice when checking your tire size include: 

DOT Symbol

Tires in the U.S. are required to have a marking showing that the tire has passed all the minimum DOT standards to be sold in the U.S. This symbol comes in the form of the letters, "DOT," which stand for the Department of Transportation. After this marking, there will be a letter and number which indicate the plant the tire was manufactured at, as well as another two letters noting the size. 

Tire Identification Number

If you see a series of letters and numbers, these are optional markings included by the manufacturer. These markers indicate tire construction, tread, and the week and year the tire was produced. 

UTQG

Uniform Tire Quality Grading, or UTQG, is a rating system created by the U.S. Department of Transportation. This system rates tires based on tread wear, traction, and temperature resistance. Ratings for this system range from A to C for traction and AA to C for temperature, with C being the bottom of the scale. It's noteworthy that these tests don't project the tire's lifespan, these rating tests are performed by the manufacturer and focus on durability. 

Maximum Tire Pressure & Load

The number before "PSI" is the maximum amount of tire pressure the tire can hold and operate with. The number before "LBS" is the maximum load in pounds that a tire can carry when the tires are at maximum inflation. While both maximums are worth knowing, it's also important to note these aren't the numbers to stick to for ideal vehicle performance. You can find recommendations for PSI and load capacity in your owner's manual. 

What Size Tires Do I Need?

You will need to check your owner's manual or visit Audi Fletcher Jones in Costa Mesa. Our tire center technicians can help you find a tire that will fit your vehicle and driving habits. 

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