Speed Rating Load Index
There’s always more to learn at Pep Boys. Here’s the word on more of the words and symbols written on your tires.
Tire Size Markings
P =Passenger Car Tire
The first letter on a tire indicates the tire’s class. P designates this tire as a passenger car tire, an LT before the tire size would mean the tire is a light truck tire, and a European metric tire would have no letter before the tire size.
245 =Section Width
The section width is the width of the tire from one sidewall to the other measured in millimeters. In this example, the tire is 245 millimeters wide.
45 =Aspect Ratio
(Ratio of Sidewall height to width)
The aspect ratio refers to the height of the sidewall, and it is a percentage of the section width. In this example, the sidewall height is 45% of the 245 section width which equals 110.25.
Z =Speed Rating
S = 112mph
T = 118mph
The speed rating designates the maximum speed at which a properly installed and inflated tire can be driven on. In this example, the speed rating is Z which means it has the highest speed rating. Z rated tires will also have a W or Y speed rating indication after the load index which denotes the actual mph the tire is rated for.
In this example, the R designates this tire as a radial tire. Radial tires have layers of fabric whose cords run at right angles to the circumference of the tire and whose tread is strengthened by additional layers around the circumference making it the most common type of automotive tire.
Wheel Diameter specifies the size, in inches, of the wheel that a tire fits. In this example, the tire will fit a 19 inch wheel.
Load Index indicates the maximum load carrying capacity of the tire. It is very important to only install tires with a load index that meets or exceeds your vehicle manufacturer's specification.
The speed rating designates the maximum speed at which a properly installed and inflated tire can be driven on. In this example, the speed rating is W which means it can be driven at speeds up to 168 mph.
U.S. Department of Transportation Markings
All tires must have a DOT, or Department of Transportation number, which indicates the tire has passed all minimum DOT standards for sale in the U.S. This code represents the manufacturer and the plant it was manufactured at (R8) and the size (LN). Also, an optional code for manufacturing (LMJR) which specifies the construction, tread pattern and category of the tire. The week (46) and year (10) the tire was produced are at the end of the code.
Uniform Tire Quality Grading (UTQG) Marking
The Department of Transportation requires each manufacturer to grade its tires under the Uniform Tire Quality Grade (UTQG) system which establishes ratings for treadwear, traction, and temperature resistance. It is important to note that these tests are conducted independently by each manufacturer and not by the Department of Transportation.
The treadwear rating (440) refers to the durability of the tire, not necessarily the projected life of the tire. Since the test is conducted by each manufacturer, and the grade is assigned after the tire has only experienced a small amount of treadwear, there is room for interpretation. While it may be helpful to compare treadwear grades within the same manufacturer, it might not be as helpful to compare the grades across multiple brands or manufacturers.
The traction rating (A) refers to the tire’s ability to stop in a straight line on wet asphalt and concrete under the controlled conditions of the test track. The test does not measure the tire’s cornering ability or hydroplaning resistance in wet conditions or braking and handling in dry conditions. The traction grades consist of AA, A, B or C, with AA being the highest.
The temperature rating (A) refers to the tire's resistance to the generation of heat when driven at high speeds. The grades range from A through C with A being the highest, making tires with an A grade most effective at dissipating heat.
Maximum Inflation Pressure and Load
This maximum inflation pressure number, (51 PSI) indicates the maximum air pressure the tire can hold while in operation. This does not represent the recommended inflation pressure for the vehicle it is installed on. You should always set your air pressure to your vehicle manufacturer’s specifications as stated in your owner’s manual or on the tire information placard inside the vehicle.
The maximum load number, (1653 LBS) is the load carrying capacity of the tire when it is inflated to the maximum inflation pressure. Similar to inflation pressure, this is not the recommended load carrying capacity for the vehicle it is installed on. You should always match the load index or load range of the tire to the specifications in your owner’s manual.
Every tire is designed to withstand a specific level of speed over an extended period of time – think in terms of highway driving for example. The longer you drive at a certain speed, the more heat a tire will generate from the friction of that tire churning against the road surface and the side wall flexing.
A tire’s speed rating indicates the ability of that tire to handle a certain level of prolonged speed – and the heat it produces – without suffering deterioration in performance.
All tires in the in the U.S. are designed to maintain legal U.S. speed limits. A tire’s speed rating must match the maximum driving speed of the vehicle it’s mounted on. However, simply installing a tire rated for a designated speed does not mean the vehicle it’s mounted on can be driven safely at the tire’s highest performance level.
Below is a list of ratings coordinated with the speeds they represent. Note: These are not recommended speeds.
|Rating||Maximum Speed||Typical Application|
|L||75 mph | 120 km/hr||Off-Road & Light Truck Tires|
|M||81 mph | 130 km/h|
|N||87 mph | 140 km/h||Temporary Spare Tires|
|P||93 mph | 150 km/h|
|Q||99 mph | 160 km/h||Studless & Studdable Winter Tires|
|R||106 mph | 170 km/h||H.D Light Truck Tires|
|S||112 mph | 180 km/h||Family Sedans & Vans|
|T||118 mph | 190 km/h||Family Sedans & Vans|
|U||124 mph | 200 km/h|
|H||130 mph | 210 km/h||Sports Sedans & Coupes|
|V||149 mph | 240km/h||Sports Sedans, Coupes, & Sports Cars|
|Z||> 149 mph, 240 kh/h|
|W(Z)||168 mph | 270 km/h||Exotic Sports Cars|
|Y(Z)||186 mph | 300 km/h||Exotic Sports Cars|
The load index is a numerical identifier assigned to each tire based on the ability of that tire’s size to withstand a certain load level of speed without deterioration in performance. The higher the load index value, the greater the load the tire can safely carry at the correct inflation.
Note: Pep Boys will only install tires that meet or exceed the original equipment manufacturers specifications for specific rating and load index.
|Load Index Value||Load(in pounds)|