The tire codes on the sidewall of a tire names the manufacturer, the model, and the tire type. These are easy to identify on your tire, but then there are also jumbles of numbers and symbols including the tire’s size information that are not always easy to understand. What do these tire codes mean? This concise guide to reading tire codes explains everything you need to know.
Tires have codes and numbers along the outer and inner edges of the sidewall. The first and most important of these tire codes is the size of your tire looking something like “P245/45R16 101H M+S”. This is the most common type of tire code, so let’s break this down.
Tire Class
Your tire most likely has a “P” rating, which means the tire is designed for a passenger vehicle, and meets US government standards for a passenger tire. Other common classes include “LT” for light trucks and SUVs. No letter means it is a Eurometric tire meeting European standards. “T” for temporary, which would be found on a spare tire.
Tread Width
Following the letter is a 2 or 3 digit number that is the width of the tire tread, in millimeters (mm). In our example, “245” means the tread width is 245 mm.
Aspect Ratio
Following the tread width is normally a slash (“/”) followed by a 2 digit number. This is the “aspect ratio” or “profile” and describes the height or the tire’s sidewall. This is expressed as a percentage of the width. In our example above, the tire’s sidewall height is 45% of 245 mm, or 110.25 mm.
Construction Type
Following the aspect ratio is the construction type. Almost all tires today have the letter “R” to indicate a radial tire. In the past, other letters were used such as “D” for diagonal bias or “B” for belted bias but such tires are extremely rare today.
Diameter
Immediately following the “R” is a 2 digit number that is the diameter in inches of the rim the tire will fit on. Our example above is a tire made for a 16 inch rim. Rims today are most commonly 15 to 18 inches in diameter, but they can be as small as 12 or as large as 24 (or even bigger on commercial vehicles like large trucks).
Load Index & Speed Rating
Usually separated from the diameter by a space, the Load Index is the “101” in our example above. This shows the amount of weight a tire can bear when fully inflated. The number—which can range from 0-179—is a code rather than the actual weight. Passenger tires are usually rated between 70 and 110. Light truck tires may be somewhat higher.
Following the Load Index is the Speed Rating, which is a letter from A-Z indicating the maximum speed the tire can handle. This is the “H” in our example. The most common ratings are Q, R, S, T, H, V, W, Y and ZR, which is the fastest speed a tire can be rated for (over 300 km/hr, or 186 mi/hr). Even though you will never go this fast, your car maker may require a ZR tire on your car for technical reasons including handling performance. Visit our blog on speed ratings for a more in-depth explanation.
Together, the Load Index & Speed Rating are sometimes called the “Service Description”.
Conditions
All-season passenger and light truck tires are marked with “M+S,” meaning they meet US requirements for mud and snow. Some tires also have a snowflake symbol, which means the tires are built to handle severe snow conditions. Winter tires will normally carry the snowflake symbol. Rarely, an all season tire may be rated for severe snow service use. Summer tires, popular on sports cars, will not have the “M+S” symbol.
Uniform Tire Quality Grading (UTQG) Standards
The US government sets standards for grading tires in 3 areas: Treadlife, Traction, and Temperature resistance. Each tire is graded based on the result of standardized testing, so these grades can be compared between tires. Treadwear is a 1 to 3 digit number (a rating of 400 should last twice as long as a rating of 200), traction is 1 or 2 letters (“AA” has the most traction; “C” has the least) and temperature is a single letter (“A” has the highest temperature resistance; “C” has the least). Visit TireVan’s blog for more information on UTQG ratings.
Some Exceptions
There are some exceptions to the prior explanation that are rare, but if they apply, important:
- Light truck tires and winter tires will not have UTQGs
- Light truck tires have an additional technical metric called Load Range. If you have a light truck tire, somewhere after the Service Description you can find the Load Range. It will generally be expressed in the form “Load Range E” or “LR E”. Common Load Range values are C, D and E. It is a measure of sidewall toughness and pressure resistance, similar to the old “Plys”, with E being the toughest.
- There are a few other sizing systems beyond the common P, LT and Eurometric described above. One is the “flotation size system” which is a type of light truck tire and usually takes the form “33×10.5-15”. This is a different way of expressing width, height, and diameter.
Beyond the size codes above, there are a few additional tire codes you may want to understand:
DOT Number
The DOT (Department of Transportation) number is a series of characters and numbers indicating the manufacturer, the plant where the tire was created, and the week & year the tire was made. All tires made after 1999 have a four-digit number where the first two digits represent the week of the year and the last two digits represent the year. Therefore, a tire labeled DOT GHYT 0301 was made in the third week of 2001. “GHYT” represents the tire maker and manufacturing plant at which the tire was produced.
Maximum Pressure & Maximum Load
Never inflate your tires with more air than the maximum air pressure indicated on the sidewall. Remember, this number is the maximum air pressure, not the recommended air pressure. You can find the recommended tire pressure for your vehicle by consulting your owner’s manual. These recommendations can often also be found on the inside of the driver’s side door frame. Also, never load your car with more passengers and weight than the maximum load limit indicated in lbs on the tire’s sidewall.
These are the most important tire codes that you should become familiar with.
Comments?
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Hey gr8 information about the vehicle tires there are so many signs which make us confused but in this you described all aspects clearly…..thanks for sharing nice post.
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