What you need to know about tire sidewall markings
What do you know about tire markings?
Ever wonder what all those numbers and letters represent on the sidewall of your tires? The writing on your tires can be quite confusing.
Most of us ignore them, but tire sidewall markings contain much more information about your tires than you realize. Apart from the tire’s brand, line names (tire model) and the tire size, the manufacturer provides a lot of information on the sidewalls of the tire.
Did you know the markings are part of Transportation Canada and safety standard markings? These markings indicate that the tire meets all industry standards and measures up to the government regulations and the safety requirements as determined by Transport Canada.
Some of the branded information gives the basic dimensions of the tire and reveals the exact week it was manufactured. Other manufacturers or brands identify the kinds of materials used to strengthen the rubber.
On top of these markings, there’s also the Uniform Tire Quality Grading (UTQG) code along with speed, load, and maximum inflation pressure specifications – just to name a few. Let us now take a closer look.
Tire Size Markings
Example: P245/45Z/R19 98W
P = Passenger Car Tire
The first letter designates the class of tire. P indicates this tire as a passenger car tire. An LT before the size of tire would mean the tire suits a light truck only. A European metric tire would’ve no letter before the size of tire.
245 =Section Width Tread (mm)
The section width refers to the width of a tire from one sidewall to another measured in millimeters. In this case, the tire is 245mm wide.
45 =Aspect Ratio (Ratio of Sidewall height to width)
The aspect ratio refers to the height of the sidewall. It’s the percentage of the section width. In this case, the sidewall height is 45 percent of the 245 section width that equals 127.5.
Z = Speed Rating S = 112mph T = 118mph
The speed rating indicates the maximum speed at which a motorist can drive on a properly installed and inflated tire. In this case, the speed rating is Z that means it has the maximum speed rating. Also, Z rated tires will have a Y or W speed rating designation after the load index which represents the actual mph rated for the tire.
R = Radial Construction
In this example, R indicates that this is a radial tire. Radial tires have fabric layers whose cords run at right angles to the tire circumference and whose tread is reinforced by extra layers around the circumference making it the most popular type of car tire.
19 = Wheel Diameter (inches)
Wheel Diameter indicates the size (in inches) of the wheel which a tire fits. In this case, the tire will fit a 19-inch wheel.
98 = Load Index
Load Index specifies the maximum load-carrying capacity of the tire. It’s imperative to install tires only with a load index which meets or exceeds the specification of your car manufacturer.
W = Speed Rating
The speed rating indicates the maximum speed at which a motorist can drive on a properly installed and inflated tire. In this case, the speed rating is W which means one can drive it at speeds up to 168 mph.
All tires must have a DOT serial number which confirms the tire meets all minimum DOT standards for sale in the United States and Canada. The code denotes the size (LN), the manufacturer and the manufacturing plant at (R8).
Also, an optional serial code for production (LMJR) that specifies the tread pattern, construction, and the tire category. You can find the week (46) and year (10) of tire manufacturing at the end of the code.
Uniform Tire Quality Grading (UTQG) Marking
The Department of Transportation necessitates all manufacturers to grade their tires under the Uniform Tire Quality Grade (UTQG) system that establishes ratings for temperature resistance, traction, and treadwear. It’s significant to note that each manufacturer conducts these tests independently and not by DOT.
The treadwear rating (440) refers to the tire durability, not necessarily the expected life of the tire. Since every manufacturer conducts the test, and it assigns the grade once the tire has experienced a small degree of treadwear. There’s room for interpretation.
Whereas it may be important to compare the grades of treadwear within one manufacturer, it might be insignificant to compare the grades across various manufacturers or brands.
The traction rating (A) is the ability of the tire to stop in a straight line on wet concrete and asphalt under well-controlled conditions of the test track. The test doesn’t measure the tire’s braking and handling in dry conditions or hydroplaning resistance or cornering ability in wet conditions. The traction grades include AA, A, B or C, with AA being the maximum.
The temperature rating (A) is the tire’s resistance to heat generation when rotating at high speeds. The range of grades from A through C with A being the highest; thus, making tires with an A grade very efficient at dissipating heat.
Load and Maximum Inflation Pressure
The maximum inflation pressure number, (51 PSI) designates the maximum air pressure the tire can hold while in operation. It doesn’t denote the recommended inflation pressure for a particular car.
Be sure to set your air pressure to the specifications of your vehicle manufacturer as stated in the owner’s manual or on the tire information placard in the car.
The maximum load number, (1653 LBS) refers to the tire‘s load carrying capacity when it’s inflated to the maximum inflation pressure. Similar to the inflation pressure, this isn’t the right load carrying capacity for a particular car.
You must always match the load range or load index of the tire to the specifications in your owner’s manual.