Understand Your Car Tire Label

Nearly all tires available today come with a label on the side. The label is generally a combination of different letters and numbers. A slash separates some of the numbers. These labels actually provide a large amount of information for anyone who knows how to read them. Each letter or number in a tire label has a distinct meaning.

Service or Tire Type

The very first letter indicates the service or tire type. This is the original intended purpose for the tire. A letter P means the tire is for passenger vehicles. This includes everything from the smallest sub-compact cars to light pickup trucks. A label that starts with LT means the tire was intended for light trucks that move freight. The letter C means commercial. These tires are means for commercial vehicles like vans and delivery trucks. ST, or special trailer, tires are designed for use on towing trailers. The last possible letter is T. A T means the tire was made to be a temporary spare.

Tire Size and Ratio

The next two numbers are usually separated by a slash. The first number is the tire size. This is simply a measurement of the width of the tire from the widest points on the inner and outer sides. The measurement is in millimeters. The second number is the tire ratio. This is the measurement of the height from the rim to the outer edge or tread in relation to the width. The measurement is given as a ratio. A ratio of 50 means the height is half the width.

Internal Construction

The next letter shows the internal construction. Nearly all tires sold today have an R in this position. This means the internal plies are radial from the center. A D means the internal plies are diagonal from the center and create an angled grid pattern. A B means diagonal construction reinforced with belts. A second letter can sometimes appear. If the second letter is an F, then the tire has a run-flat internal structure that can support itself.

Rim Diameter

The letter on the tire label immediately after the internal construction letter is the rim diameter. This is the distance between the bead seats on the tire. If the rim diameter is less than 32, then this number is the measurement in inches. If the number is higher or over 100, then it is in millimeters. In some rare cases, this measurement will include fractions or decimals.

Speed Rating and Load Index

The label ends with a letter and a number. The letter is the speed rating. This letter shows how fast the tire can go before coming apart. This letter could be S, H, V or Z. Those letters mean 112, 130, 150 or greater than 150 miles per hour respectively. The number with the letter is the load index of the tire. This number references an indexed chart. Looking up the number on the chart will show how much weight four of the same tires can support safely.