Reading Tire Information
Your tire’s side exterior (sidewall) has some letters and numbers engrave all over them. These are vital information about your tire. They will tell you everything you need to know about them.
Sidewall is the external portion of the tire that is visible. You might have noticed that your tires have some letter and numbers written on it. Have you ever thought what are those for and what do they mean. Okay, so you didn’t. Let us start by saying that these are very critical information about your tires. They consist details such as size, expected life (tread life), speed and much more. Let us uncover it for you one by one.
The first thing you will notice is alpha numeric combination, for e.g. “P225/50R18” followed by “89H M+S”.
Lets take a look at “P225/50R18” first. The letter P over here stands for passenger metric. You may often come across “LT” which means light truck, “ST” for special truck, “T” for temporary spare, etc. These are Euro metric size and you will often find that there is no letter but that is normal.
The “225” indicates the tire’s width that is measured and expressed in millimeters.
After that you have “50”. The “50” is the aspect ratio of the tire which basically denotes that the sidewall of the tire is 50% of what the tire’s width is. “
“R” means radial construction and “18” is the diameter of the rim.
Now lets talk about the next set, i.e., “89 H M+S” 89 is the load index of the tire and H indicates the speed rating.
Learn more about speed rating.
The table below shows various speed ratings and their meaning.
“M+S” means mountains +Snow. This indicates that the tire is suited and made especially for severe snow conditions.
Few other things that you will notice and we will cover are
DOT is an abbreviated form of Department of Transportation safety code. DOT of a tire is expressed with 12 digit alphanumeric combination. The code consists of information such as the manufacturer and plant code (plant code is where the tire was made). The end 4 digits tell you about the week and the year the tire was manufactured. It helps you determine the age of the tire.
Uniform Tire Quality Grading will tell you about three crucial factors treadwear, traction and temperature. “Treadwear 200 Traction AA Temperature A”. The grading system was established by National Highway Traffic Safety Administration (NHTSA). NHTSA has standard methods of testing tires that manufacturers need to follow and then grading them accordingly.
A bit more in detail:
1) Tread wear: Tread wear is the life expectancy of a tire. The grading system is a comparison of a tire to the other tires made by the manufacturer. 100 is the baseline grade. So if a tire from same manufacturer has 200 rating and the other tire has 100. This means that the 200 tire will last twice than the other one.
2) Traction: Traction means grip. The traction ratings are given based on the performance of the tire. It tells us how the tire has reacted to the brake pedal when it was pressed under the wet pavement. The government has set the standard of the pavement for test. There are four gradings “AA, A, B and C”. C is the lowest of all and unacceptable. The grading provided is strictly for straight line wet coefficient of traction.
3) Temperature: Temperature rating states how well a tire can handle heat. The gradation is given after testing the tires in an indoor test conditions. The ratings given are A, B and C. C is the lowest therefore unacceptable for roads. The C rating tires are those that will give problems at high speed.