A tire’s sidewall is pretty much what it sounds like – the outer and inner "walls" on the sides of a tire, if facing a tire on its side. Every sidewall has its own unique information that is divided into three main sections:
This describes the fundamental characteristics of your tire. Size, construction, speed rating and more.
Tire Type Commonly you may find the letter "P" at the beginning of the size information. For example, the letter "P" denotes that the tire is for a "Passenger Vehicle" meeting the standards for use in the United States, intended for Passenger vehicles.
Width This is the the tire width measured in millimeters from sidewall to sidewall. In this example, the tire is 225 millimeters wide from sidewall to sidewall.
Aspect Ratio This is the ratio of the height of the tire's cross-section to its width. The two-digit number after the slash mark in a tire size is the aspect ratio. For example, this P225/60R15 tire, the 60 denotes the height of the sidewall is 60% of the width of the tire.
Construction The letter "R", common in most tires denotes that this tire's construction is "RADIAL" - a popular, reliable and very common construction type.
Wheel Diameter Your tire's diameter is the size of the wheel it's intended to fit on, measured from one edge to the other. A size P225/60R15 tire is designed for a wheel with a 15" diameter.
Load Index The load index number and speed symbol correspond to the maximum load-carrying capacity of the tire and its maximum speed capability. The load index is an assigned number that corresponds with the load-carrying capacity of the tire. For example, "96" indicates a load-carrying capacity of 1565 lb. at maximum inflation pressure. The load index for most passenger car tires ranges from 75-100.
Speed Rating Speed ratings are determined by indoor laboratory testing methods, which measure high-speed tire durability under controlled test conditions. These test procedures do not take into account underinflation, tire damage, vehicle characteristics or road conditions which can lead to sudden tire failure or loss of vehicle control at much lower speeds than indicated by the tire's speed rating.
Department of Transportation Safety Code
This assures that your tire complies with all Department of Transportation (DOT) safety standards. After the DOT insignia is your tire’s identification number, which begins with the tire’s manufacturer and plant code where the tire was manufactured (two numbers or letters). The ninth and tenth characters tell the week the tire was manufactured. The final number(s) signifies the year the tire was manufactured.
The Uniform Tire Quality Grading (UTQG) was established by the National Highway Traffic Safety Administration (NHTSA) to test tires following government prescribed test methods and then grade each tire on three main components:
Treadwear This is the wear rate of the tire, comparable only to other tires within a tire manufacturer’s line. 100 is the baseline grade. Therefore a tire with 200 would theoretically last twice as long on the government’s course compared to a tire with 100.
Traction Traction grades are AA, A, B and C (with AA being the highest grade). They represent the tire’s ability to stop straight on wet pavement as measure on a specified government track. Any tire rated under C is considered unacceptable for road travel.
Temperature The temperature grades, from highest to lowest, are A, B and C. These represent the tire’s ability to dissipate heat under controlled indoor test conditions. Any tire rated below C is considered unacceptable.