Tire Sidewall Information
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Table of Contents
There is a tremendous amount of tire information displayed on the sidewall and this lesson covers every piece of information in detail. The car owner, and most definitely technicians, need to be familiar with what this information means.
Tire Type: Passenger / Light Truck
The first character defines the tire as a passenger or light truck tire as follows:
- “P” or no letter – Passenger car tire – The tire in the image below does not have a beginning letter, therefore it is a passenger car tire.
- “LT” – Light truck tire – These tires are built heavier and are not specifically designed for passenger car applications.
The tire’s tread section (as illustrated below) measures 225 millimeters (mm) wide.
The sidewall’s height (as illustrated below) is 50% of the tread’s width of 225 mm. Cars with small sidewall ratios are commonly called low profile tires.
YouTube Video: Aspect Ratios in Tires
The “R”, as illustrated in the image below, indicates the tire is a radial design. The cords of the tire are wrapped in a radial fashion other than on an angle which is called a bias-ply tire. Since the automotive tire industry switched to radial-ply tiers in the mid 1970s, it is not always listed, but implied.
The diameter of the rim, as illustrated in the image below, is 17″. Note that some rim diameters are defined in millimeters, not inches.
The tire, shown in the image below has a 98 load index, which is 1,659 pounds. This is the highest load the tire is capable of safely carrying.
Load Index Table
This load index table shows the maximum weight, per tire, in pounds.
The tire sidewall, in the image below, indicates an “H” speed rating, which is 130 MPH. This is the highest speed the tire is designed to safely reach and maintain.
Tire Speed Rating Table
|Letter||Maximum Speed||Type / Vehicle Use|
|L||75 mph / 120 km/h||Off Road & Light Truck Tires|
|M||81 mph / 130 km/h||Temporary Spare Tire|
|N||87 mph / 140 km/h||Temporary Spare Tire|
|Q||99 mph / 160 km/h||Winter 4X4|
|R||106 mph / 170 km/h||Heavy Duty Light Truck|
|S||112 mph / 180km/h||Family Sedans & Vans|
|T||118 mph / 190 km/h||Family Sedans & Vans|
|U||124 mph / 200 km/h||Sedans & Coupes|
|H||130 mph / 210 km/h||Sport Sedans & Coupes|
|V||149 mph / 240 km/h||Sports Cars|
|Z||149+ mph / 240+ km/h||Sports Cars|
|W||168 mph / 270 km/h||Exotic Sports Cars|
|Y||186 mph / 300+ km/h||Exotic Spots Cars|
Most tires have tread that works equally well in either direction, but some tires are designed to give superior performance when rolled in a specific direction. The tread on directional tires tend to look like a “V”, as shown in the image below, and is designed for moving water to the outside of the tire better than a standard tread design.
Directional tires will designate the direction of rotation on the sidewall, as shown in the image below. If the directional tire is rotated to the opposite side of a car, the tire would have to be flipped around on the rim to keep the direction of rotation correct.
The tread pattern on an asymmetrical tire is not the same on the inner and outer part of the tread. One side of the tread is designed for better cornering and one side is designed for better braking.
Asymmetrical tires will have markings on the sidewall to designate which side of the tire goes to the outside when mounting the tire on the rim.
Asymmetrical and Directional Tire
A tire that is both directional and asymmetrical is rare and designed for high-performance applications. Since the tire is designed to roll in one direction and the inner part of the tread is different than the outer part of the tread, the tire is sold as left and right side tires (two different part numbers).
YouTube Video: Asymmetrical / Directional Tires
Other Sidewall Information
Tire Build Date
Every tire sold in the US market must have a Department of Transportation (DOT) serial number. The last four numbers of the serial number contain the build date code as (Week of Manufacture | Year of Manufacture) In the image below, the date of manufacture is the 51st week of 2007.
Uniform Tire Quality Grading (UTQG)
In 1978 the National Highway Traffic Safety Administration (NHTSA) developed the UTQG system so consumers could compare key features between tires. In 1979, the Department of Transportation (DOT) federally mandated UTQG ratings on the sidewall as part of the DOT approval process.
NHTSA provides the two following resources for looking up UTQG ratings on specific tires:
- Hard Copy – NHTSA periodically produces a large PDF that compares UTQG information on all tires sold in the USA. The most current PDF (2016) can be downloaded here.
- Online Lookup – NHTSA offers an online lookup tool that supports looking up tire information by brand and tire line.
Treadwear is an index that indicates a tire’s relative wear rate. The higher the treadwear number, the longer it should take for the tread to wear down. Each tire manufacturer builds their own control tire and assigns a treadwear of 100. All the tires made by each manufacturer are compared to their own internal control tire. This means you can use the treadwear index to compare relative tire wear within the same tire manufacturer, but not across different manufacturers.
For example, a tire with a Treadwear rating of 200 should wear twice as long as the manufacturer’s control tire.
Tread wear percentages of all tires currently being sold in USA:
- 2% are rated above 600
- 6% are rated 501 – 600
- 20% are rated 401 – 500
- 32% are rated 301 – 400
- 25% are rated 201 – 300
- 15% are rated below 200
Traction grades are an indication of a tire’s ability to stop on wet pavement. A higher graded tire should allow a car to stop on wet roads in a shorter distance than a car with a lower grade. Traction is graded from highest to lowest as: “AA”, “A”, “B”, and “C”
Traction grade percentages of all tires currently being sold:
- 15% are rated “AA”
- 77% are rated “A”
- 7% are rated “B”
- Only 4 lines of tires are rated “C”
Temperature grades are an indication of a tire’s resistance to heat buildup. Sustained high temperatures (for example, driving long distances in hot weather or carrying heavy loads at high speeds) can cause a tire to deteriorate, leading to blowouts and tread separation. From highest to lowest, a tire’s resistance to heat is grades as “A”, “B”, or “C”.
- 62% are rated “A”
- 34% are rated “B”
- 4% are rated “C”