What Do Tire Numbers Mean
Taking a thorough gaze at your car tire, you will see some numbers written on the sidewall of the tires. These numbers that are written on the sidewall of the tires provide very important information regarding the tires. Information like the size, the load bearing capacity, the amount of pressure that the tire can take, what type of vehicle it can be used on, and so on are represented by those numbers.
Are you worried about decoding the codes? You’ve been to the right place! This article will teach you what all these numbers mean and at the end, you will be a pro in reading numbers written on the sidewall of the tire.
Meaning Of The Tire Numbers
The numbers written on the tire’s sidewall are meant to give guidance about the usage of the tire. The numbers can be written as:
P215/50R17 91S or 217/40R18 90S
The meaning of the letters and numbers above is further explained below:
First Letter Or Letters Before The Three-Digit Numeric
Most of the numbers branded on the sidewall of tires have letters written before them. Some which can be P, LT, ST, T and some may not have letters written there. The letters mean what type of vehicle the tires can be used on. See below:
- P (Passenger car) - When tire numbers begin with P, it means the tire is a “P-metric”. It means it is engineered to work primarily on passenger vehicles and examples of these vehicles are light weight trucks, minivans, cabs, sport utility vehicles and other vehicles that are lightweights. These types of tires are mostly used today.
- LT (light truck metric) - This means that the tire is designed to be used on vehicles that are engineered to carry the heavy load or towing large trailers. Examples of the vehicle that can use this kind of tires are the heavy sports utility vehicles, pickup vans, full-sized vans, and the like. These tires are designed to be able to withstand the additional weight they will carry.
- T (Temporary) - If T is written on the sidewall of the tire it means the tire is designed to be a spare tire. It is supposed to be used when there is a flat tire until the tire is repaired or replaced.
- ST (Special Trailer) - If ST is written on the sidewall of the tires, it means that it is engineered to be used for special services. Such tires are commonly designed to be used on boats, aircrafts and utility trailers. The ST-sized tire is not appropriate for small vehicles and van and should never be used on them.
If there is no letter written before the three-digit numeric, it means the tire is a “metric” size. Metric size is also referred to as “Euro-Metric” because this design came from Europe. The metric or Euro-metric tires are usually used on European cars but they can also be used on vans and sports utility vehicles. These types of tires are designed to be of the same size with the P-metric tires but their load bearing capacity are different.
The 3-Digit Number (Example: P225/50R17 91S)
The numbers are usually written next to the letter and it identifies the cross section width of the tire. It is usually written in millimeter. It is measured from sidewall to sidewall on the outer part of the tire. Moreover, it is also known as the tire’s section width.
The 225 in the example above means the tire is 225mm from sidewall to sidewall of the tire. The number can also be converted into inches. 225 mm is equivalent to 25.4 inches.
The 2-digit number (Example: P225/50R17 91S)
It is called the “aspect ratio” and it is usually written next to the cross section width of the tire. In this number, the aspect ratio of the tire is 50, which means that the sidewall of the tire (from rim to tread) is 50% of the cross section width. This means the higher the number the taller the sidewall of the tire. There are some tires in which the aspect ratio is not written. This means that the aspect ratio is 82% of the sectional length.
The Letter After The 2-Digit Number
This letter refers to the internal construction of the tire. It is usually written immediately after the aspect ratio. The letters can be R, B, and D. What each of these letters mean is enumerated and explained below:
R - When R is written it means that the tire has a Radical design in which the body of the tire plies “glows” out from the imaginary center of the wheel. These types of tires are the most popular type of tires that are produced today.
If “R” is replaced with “B” it means the tires are supported with belts under the thread area. These types of tire design are normally called Belted but are no more in use today.
If the “R” is replaced with “D” it means the internal tire is moving in an intersecting Diagonal way. Such tire also has a type of construction that is referred to as “bias ply”. The type of vehicles using this type of tire is a light truck and they are mainly used as spare tires.
These 2-digit numbers refer tp the diameter of the rim. It is usually measured in inches. The most common type of rim sizes are 8, 12, 13, 14, 15, 17, 188, 19, 20, 22, 23, 24, 26 and 28. The types of rim sizes listed above are used mostly on minivans, sport utility vehicles, vans, and light trucks.
The 2-digit and letter combination
It is usually called the service description. It recognizes the load index (the 2-digits) and the speed rating (the letter V) of the tire. The service description is needed on all speed rated tires.
Now, you know what the numbers branded on your car tires mean and can even explain it to others like a pro. You can now choose the appropriate tire for your vehicle without taking it to any tire expert. You can even secretly decode the numbers written on the sidewall of your tire. Everything written on the tires were not there as designs but as information that will guide you in choosing the appropriate tire for your vehicle.