Introduction:
This PDF has been created for informational purposes to help answer any questions you might have on tire sizing and ratings (Passenger Car tires only). After reading this PDF you will understand:
* What is printed on the sidewall of a tire
* How to quickly read and understand tire ratings
* How to determine the speed and load ratings of a tire
* How to use all of this knowledge to find the appropriate tire to fit your needs and your vehicle
What’s on your sidewall:
How to read the sidewall of a tire:
Tire Type:
The letter “P” at the beginning of the tire code tells us that this is a tire which is made to the required specifications to be used on passenger cars in the United States. Other examples of tire types include “LT” for Light Truck tires, “ST” for Special Trailer, and “T” for Temporary tires (more commonly known as “donut” or “space saver” spare tires.
Tire Width:
The three-digit number following the tire type code is the width of the tire measured in millimeters from sidewall to sidewall. The tire in the example has a width of 225mm.
You can convert the width measurement from millimeters to inches by dividing the width by 25.4. For example: 225mm / 25.4 = 8.86”
Aspect Ratio:
The two-digit code following the slash mark is the aspect ratio of the tire. This number represents the relationship between the width of the tire
and the height of the sidewall. For example: The tire shown has a width of 225mm, and the aspect ratio is 40%. To calculate the height of the sidewall we multiply the width by the aspect ratio: 225 x 40% (0.40) = 90mm.
You can convert the sidewall height from millimeters to inches by dividing the height by 25.4. For example: 90mm / 25.4 = 3.54”
Tire Construction:
The letter code following the aspect ratio identifies the tire’s internal construction. In our example, we see the letter “R”, which means this tire has a Radial construction. Radial tires are the most popular type of tire sold today representing over 90% of all tires sold.
Wheel Diameter:
The two-digit number after the tire construction code tells us the diameter of wheel that the tire is designed to fit on.
Load Index:
This number indicates the maximum load that the tire is rated to support when properly inflated. The maximum load capacity can also be found printed on the tire sidewall, and it will be in both pounds and kilograms. To see a chart with the most common load indexes and their capacity, please see page 10.
Speed Rating:
The speed rating tells you the maximum speed the tire is capable
of operating at. Usually speed ratings are matched to the top speed capability of the vehicle. To see a chart with the most common speed ratings please see page 10.
Treadwear Rating:
This number is based upon standardized government tests which help to predict the expected treadwear of a tire. For example, a tire which has a treadwear rating of 200 is expected to last twice as long as a tire which has a treadwear rating of 100.
Traction Grades:
Temperature grades indicate the ability of the tire to withstand and dissipate the destructive heat that comes from operating at higher speeds. A tire with an “A” temperature grade is able to operate at higher speeds than a tire with a “B” or “C” grade.
Tire Tread Rating:
If a tire has some sort of combination of M & S (M+S, M/S, MS, etc.) on
the sidewall, it means that the tire has been rated for use in mud and snow. This rating means that this tire meets the required criteria for winter traction on passenger cars.
Tires can also be marked with a combination of M & T (M+T, M/T, MT, etc.) on the sidewall, meaning that the tire is designed to perform in mud and other terrain requiring additional traction such as on rocks, loose gravel, and deep snow.
Date Code:
Any tire which has been manufactured since 2000 is required to have the date code printed on at least one sidewall. This date code is printed in a four digit number which identifies the week and year the tire was manufactured in. In our example we see a date code of 5107, this tells us the tire was manufactured in the 51st week of 2007.
Tires manufactured before 2000 were only required to have three digit date codes, based on the assumption that the tires wouldn’t be in service after 10 years. In this case our example would then read 517, meaning the tire was manufactured in the 51st week of the 7th year of the decade.
You Are Ready To Find The Perfect Tire To Fit Your Needs!
