If you are wondering which tire size and type to choose for your vehicle, it is imperative that you learn how to decipher the information that is branded on the sidewall of a tire. The branded letter and number codes provide all the necessary information you will need to know about a tire. For the purpose of clearly elaborating on tire sizes, we will use a primary example of the tire code P215/50 R17 95W.
1. Vehicle Type
The first letter in a tire label illustrates the type of vehicle that the tire is designed for. In our example, the letter indicated is P. This means that the car is designed for passenger cars. Other initial letter codes include T for Temporary Spare. This means that the tire should only be used temporarily in the event of a flat tire. LT stands for Light Truck, while ST means Special Trailer.
If there is no letter before a tire code, it means that the tire is a Euro-metric, that is, it is mainly designed for European cars, but can also be used on sport utility cars and vans. These tires are dimensionally similar to P-tire sizes, but differ slightly in the load size they can carry.
2. Tire Width
The three-digit numbers that follow the opening letter(s) indicate the tire’s width in millimeters. In our tire code example, the width of the tire is 215mm, having been measured sidewall to sidewall.
3. Aspect Ratio
The first 3-digit code indicating the tire’s width is followed by a slash and after that, a second 2-digit number. This number indicates the tire’s aspect ratio or profile, that is, width to height percentage. The number 50 in our example means that the tire’s sidewall height is 50% of the section width. Generally, tires that have lower aspect ratios are considered as performance tires.
4. Internal Construction
Following the aspect ratio number is a second letter, in our case, R, which means Radial construction. This indicates that the tire’s plies radiate or exude out of the wheel’s imaginary center. R tires are the most common kind of tires available today.
5. Rim Size
The number following the internal construction letter is the rim size, and for our case, it is 17. This means that the tire fits a 17-inch rim or wheel size. Rim sizes are generally available in a range of 8-28 inches.
6. Load Index
The rim size number is followed by another number that indicates how much load a tire can handle, that is, its load index. Our tire’s load index is 95 meaning each tire can carry 1521 pounds. By referring to the Maximum Load-Carrying Capacity table, you will be able to know much 4 tires with the same load index can comfortably carry.
7. Speed Ratings
The last letter on a tire code points out the tire’s speed ratings. In our example, the rating is W, which indicates a max speed rating of 168mph. Other ratings that indicate the maximum speed in mph include S-112, T-118, U-124, H-130, V-149 and Y-186. Exceeding a tire’s speed rate will increase friction, which will cause the tires to heat up. Overheating will cause the tire’s treads to detach from the belts.