Most consumers are aware that the outside sidewall of their tires (the side facing you when you look at your vehicle), contains basic information on maximum inflation pressure, tire size, tire manufacturer, maximum load, and perhaps the tire’s speed rating. But many consumers do not know that there is much more information available on both the outer- and the inner- or axle-side sidewall of every tire, including the tire’s date of manufacture.
The following is a brief description of some of these terms, and important information that you should know about your tires:
Maximum Inflation Pressure: most know that the sidewall of their tires contains information on maximum inflation pressure. Many do not know that this does not necessarily tell you the correct inflation pressure for the tire on your particular vehicle. Vehicle manufacturers place this information on a placard which is usually located inside the driver’s side door jamb. For various reasons, some manufacturers recommend a tire pressure below the maximum pressure of your tires, or suggest that you inflate your tires to their maximum pressure only if you are also subjecting them to maximum load. Tire and vehicle manufacturers sometimes use this little known fact to suggest that consumers have improperly inflated their tires when they fail, thus blaming the consumer for “misusing” their tires. In fact, the vehicle manufacturer recommendation may be the result of the manufacturer trying to reduce the roll-over potential of their vehicles. On the Ford Explorer, for instance, Ford told consumers for the better part of a decade (with Firestone’s consent) to inflate their original equipment Firestone tires well below the maximum pressure found on the tire’s sidewall, because Ford figured out through testing that the vehicle was less prone to roll-over under these conditions. The problem is that the lower pressure made the original equipment Firestone tires on those vehicles prone to disintegrate through normal use.
DOT Number: The federal government requires that all tires sold in the U.S. contain a Department of Transportation (DOT) number. The DOT number contains very important information about your tire that most people do not know is there. However, the DOT number is often found on the axle side of your tires, meaning you have to crawl under your vehicle or put the vehicle on a lift to read it. Perhaps the most important information contained in the DOT number is the date of manufacture of your tire. Many U.S. and foreign tire companies are now warning consumers in Europe and Asia to discard even new appearing tires that are five or six years from the date of manufacture. This is because the rubber and other components in tires break down over time, making older tires potentially dangerous even if they look brand new. Although manufacturers do not give similar warnings in the United States, this is likely to change as lawmakers and watchdog groups including trial lawyers put additional pressure on tire companies to follow the same safety guidelines that are applied overseas.
To determine the age of your tire, find the last three or four numbers on the DOT code – these represent the week and year the tire was built. As an example, the last three numbers "089" might signify that the tire was born on the eighth week of 1999. Unfortunately, not all manufacturers supply the decade, so this tire might be a 1999 or a 1989 model. Fortunately, the government has seen fit to resolve this confusion in the new millennium, so tires being built now have four digits: two for the week and two for the year. Be sure you know the age of your tires, and don't risk your safety for the few dollars (relative to an accident) that a new set of tires will cost. This is especially true for your spare tire. Your spare may have been exposed to the sun, or may have been placed near the heat of your exhaust pipe. If so, it is likely that the rubber compounds in your spare have been substantially weakened even if the tire looks brand new, which could cause a catastrophic failure if you later place the spare into service. If your spare is more than 5 years old, consider replacing it when you buy a new set of tires, even if the spare has never been used.
The DOT number also tells you who manufactured your tire. Many tires display brand names like Sears or Pep Boys, but neither company makes tires. To determine the actual manufacturer, look at the first two numbers of the DOT code. They are the plant code where the tire was made, so you can determine not only the company which actually made your tire, but at which plant it was build. A lengthy list of manufacturer codes can be found here .
Tire Size (i.e., P215/65 R 15). This set of letters and numbers represents the tire size. The “P” stands for Passenger. If there is an “LT” in the size, it designates Light Truck. The “215" represents the width in millimeters; “65" is the ratio of the height to width; “15" is the rim diameter in inches.
Speed Rating: Each tire is assigned a rating from A (lowest) to Z (highest). There is one notable exception: the "H" rating falls out of sequence between "U" and "V," and is used for tires certified for speeds up to 130 mph. The Q rating is the lowest commonly used for passenger cars.
Treadwear is a measurement of tread durability. Tested against an industry standard, the assigned numerical grade indicates how well the tread lasts compared with a reference standard of 100. A treadwear rating 200 means the tread wears twice as well as the standard. Actual wear depends on the conditions under which the tire is used. Driving habits, service practices, inflation pressure, differences in road surface and varying climates all affect treadwear.
Traction is a measurement of a tire's ability to stop on wet test surfaces of asphalt and concrete under controlled conditions. Traction grade is determined only for straight-ahead, wet braking on concrete and asphalt. It doesn't include cornering.
- Traction Grade A: The tire performed well on both surfaces.
- Traction Grade B: The tire performed well on at least one of the surfaces.
- Traction Grade C: The tire performed poorly on one or both of the surfaces
Load Range: Your tire also may have a load range designation. Typically, higher load range tires (for example, E rated tires, which are rated for a higher load than C or D rated tires), need to be inflated at or near their maximum pressure to safely carry the load for which they are rated.
Warning Information: Your tire likely has a warning not to use the tire in an under-inflated or overloaded condition. In the future, your tires may also carry a warning to replace them after a number of years, depending upon the manufacturer (5 to 10 years).
Also for your use - “Tire Plant Codes” and “Codes by Manufacturer”