All tires come in different styles, tread patterns and sizes. When it’s time for you to purchase a new tire, knowing to choose the appropriate size for your wheels is important. If you’re fortunate enough to have access to a great tire shop, 4×4 mechanic or auto service center, they can help you with this process, but it’s always great to know how to read tire specifications in case you get a flat, need to know what psi to inflate it to, or want to have comfort knowing you’re purchasing the right tire for your off-road vehicle.
First we will look at how to read the tire size. For this example, we will look at a tire that has P265/70-R16 printed on the tire.
Tire Class – “P”: The first character in a tire size is usually a letter, which designates the tire’s class. In this particular example, a “P” indicates that the tire is a “passenger” car tire. “LT” stands for a “light truck” tire, “T” stands for “temporary”, “ST” stands for special trailer”, “C” stands for “commercial and no letter before that indicates it’s a European metric tire.
Section Width – “265”: A tire that is measured in the metric scale will have the section width displayed in millimeters. In this case, 265 stands for the section width of the tire is 265mm wide.
Aspect Ratio – “70”: This number refers to the height of the sidewall. In this particular example, the sidewall measures to be 70% of the section width.
Tire Construction – “R”: The “R’” in this example indicates that the tire is a radial tire. “D” indicates a “diagonal” construction and “B” stands for “belted” construction.
Wheel Diameter- “16”: This number indicates the wheel diameter in inches. In this particular example, the wheel (or rim) has a 16in diameter.
Size (High Floatation):
Some tires may also contain a secondary size, which may be organized in a way such as this: 35×1350 R 16/E.
Diameter – “35”: The first number indicates the tire’s diameter in inches. This particular example shows that the tire is 35in in diameter.
Tire Width – “1350”: Tire width is measured in inches with the decimal point removed. In this example, the tire is 13.5” wide.
Tire Construction – “R”: As mentioned previously the “R” stands for a radial construction tire.
Wheel Diameter – “16”: Wheel diameter refers to the diameter in wheel, or rim size.
Plies – “E”: This letter indicates the load capacity of the tire regarding to its construction. “C” indicates a 6-ply load carrying capacity, “D” is an 8-ply, and “E” is a 10-ply rating. If there is no letter, the tire has a standard 4-ply rating.
Load Index and Speed Rating:
If a tire has a number printed followed by a letter, this may be referring to the load index and speed rating. In this particular example, our tire has 97H printed.
Load Index – “97”: The load index indicates the maximum amount of weight a tire can safely carry. Load indexes generally range from 0 to 279. Most tires have a load index between 75 to 105.
Speed Rating- “H”: A tire receives its speed rating from the government by meeting specific standards for reaching and sustaining certain speeds.
Tread-wear, Traction and Temperature:
Some tires will have the tread-wear, traction info and temperature info printed on the size.
“Tread-wear” will be printed on the tire followed by a number, which indicates the tire’s durability. The higher the number, the more durable a tire is and gives an indication as to how long it will hold.
“Traction” may be also printed, which is a measurement of a tire’s ability to stop. Traction grades are indicated by the letters AA, A, B and C, with AA being the highest possible.
“Temperature” will provide you information on a tire’s temperature rating. It is a measurement of a tire’s resistance to heat under normal operating conditions. Temperature grades range from A to C, with A being the highest rated and most resistant to heat generation.
Maximum Load Limit and Air Pressure:
Tires will often indicate their maximum weight capacity and maximum air pressure (psi). A tire will indicate its maximum load carrying capacity in kg and/or lbs. This provides information on how much weight a tire can handle at its recommended psi. They will also have information on the maximum air pressure measured in pounds per square inch (psi). The tire manufacturer recommends you do not exceed this inflation pressure.