Modern tires use a combination of materials to contain pressurized air. The foundation of the tire is the plies (layers of nylon, polyester, fiberglass or steel) just beneath the tread that provides flexibility and strength. Regardless of size, cost or brand, there are only three types of tires-bias, bias-belted, and radial, now the standard on all passenger vehicles.
Bias tires, the old stand-by, are constructed with cords running across the tread (from bead-to-bead) at an angle about 35° to the tread centerline; alternate plies reverse direction. Crisscrossing adds strength to the tire sidewalls and tread. When properly inflated, these tires give a relatively soft, comfortable ride.
Bias-belted tires are similar, but additional belts of fiberglass or rayon encircle the tire under the tread. The belts stabilize the tread, holding it flatter against the road with less squirm (side movement). Belted tires offer a firmer ride, better traction, improved puncture resistance and longer life than bias ply tires. Bias tires are now found mainly on antique vehicles to preserve their original appearance, and in some commercial applications.
Radial tires now rule the road as they are original equipment on virtually every passenger car and light truck. Radials are constructed with steel or fabric carcass plies crossing the tread at approximately a 90° angle, and two or more belts circle the tire under the tread. The sidewalls flex while the tread remains rigid, accounting for the characteristic sidewall bulge of a radial. The tread runs flatter on the road with a better grip and the inherently harsher ride is offset by superior handling and mileage.
Maintaining correct tire pressure is the most important factor in reducing tire wear.
Under-inflation results in unnecessary tire stress, irregular wear, loss of control and accidents. Industry experts agree that under inflation causes most drivers to lose from 10% to as much as 50% of tire tread life. It is a fact that tires lose pressure each day, through the process of permeation. In cool weather, a tire will typically lose one or two pounds of air per month. In warm weather, it's common for tires to lose air at an even higher rate. Check your tire pressure monthly or drop by one of our stores to have your tire pressure checked.
Proper tire care and safety is simple and easy. The Rubber Manufacturers Association (RMA) recommends taking five minutes every month and before every long trip to check your tires, including the spare.
You lose air pressure every month when the temperature changes.
Visit any of our locations for a
Free Tire Pressure Check.
Understanding your tires begins with understanding how to read the information printed on the side of your tire. This information is explained in detail below beginning with information about the tire size:
(commonly referred to as the "Performance Rating")
A tire's speed rating represents the maximum recommended speed that the specified tire should be driven for a specified time period. The speed rating is determined by manufacturer testing to meet the minimum standards as specified by the U.S. Department of Transportation (DOT) for reaching and sustaining a specific speed level.
A common misunderstanding about speed ratings is the consumers thought that "I never drive that fast...". While that statement is true for most drivers, the Speed Rating is directly related to the tires construction. The tire's construction directly affects the performance and handling characteristics of the vehicle.
If the vehicle manufacturer specifies a specific speed-rated tire, the replacement tires must have the same or higher speed rating. This ensures that the performance and handling characteristics and speed rating specified by the manufacturer are maintained.
If tires with different speed ratings are mounted on the same vehicle, the tire or tires with the lowest rating will limit the tire-related vehicle speed.
Tire DOT Code
The DOT code is an alphanumeric code that appears on the sidewall of the tire. This code is sometimes referred to as a serial number. It's mandated by the U.S. Department of Transportation, and identifies where a tire was manufactured, specific characteristics about the tire, and its age.
The code in the illustration at left is
DOT H2U1 YC7L 3805
H2 identifies the plant that manufactured the tire.
U1 is the tire size code.
YC7L is an optional code that refers to a brand, or other characteristics specific to the tire.
3805 identifies the manufacturing date. The first two digits represent the week, and the last two digits represent the year. Therefore, in this example, the tire was manufactured in the 38th week of 2005.
The load index is identified on the tires sidewall. In the illustration at left, the load index is 95. Simply explained, the load index on a passenger car tire is a numerical code stipulating the maximum load (mass, or weight) each tire can carry. A tires load carrying ability is affected by air pressure. The maximum load carrying capacity is attained by inflating the tire to it's maximum rated air pressure. Proportionately, the lower the air pressure, the lower the tires load carrying ability. The Load Index of the tire in the illustration is 95, in the chart below note that a tire with a Load Index of 95 has a load carrying capacity of 1521 pounds or 690 kilograms. Manufacturers specify Load Indexes, Load Ranges, and Speed or Performance Ratings and Sizes for all vehicles. When buying replacement tires it is always advisable to purchase tires that meet or exceed the manufacturers original specifications. Tires that have the incorrect load index may perform poorly, wear prematurely and potentially be a safety hazard!
The Uniform Tire Quality Grading (UTQG) system was developed by the Department of Transportation (DOT) to assist consumers in the purchase of their tires by providing a standard grading system used by all tire manufacturers. Using UTQG Standards tires have three specific areas of measurement. Traction, Tread Wear and Temperature. The grading system is alpha numeric. Let's use the following as an example of a UTQG rating:
- Tread Wear
The tread wear grade (400 in the example) is a comparative rating based on the wear rate of the tire when tested under controlled conditions on a specified government test track. A tire graded 200 would wear twice as long on the government test course under specified test conditions as one graded 100. In our example the tire would last 4 times as long as a tire with a rating of 100. To estimate mileage using the UTQG tread wear grade, 100 is equals 10,000 to 12,000 miles. A rating of 400 would be about a 48,000 mile tire. This is an "estimate" not a guarantee, actual mileage will vary based on driving habits and conditions. Most manufacturer's actually specify a mileage warranty, ask for details or visit the manufacturers web site for more information.
Traction grades, from highest to lowest, are AA, A, B and C. They represent the tire's ability to stop on wet pavement as measured under controlled conditions on specified government test surfaces of asphalt and concrete. The testing does not take into account cornering, hydroplaning or acceleration.
The temperature grades, from highest to lowest, are A, B and C. These represent the tire's resistance to the generation of heat.
UTQG is in effect now; however, NHTSA issued a press release in June of 2009 proposing a new more consumer friendly tire labeling system. Press release is below:
U.S. DOT Proposes New Tire Fuel Efficiency Ratings for American Consumers
NHTSA Thursday, June 18, 2009 -- The U.S. Department of Transportation today proposed a new, consumer-friendly replacement tire label which would include, for the first time, information about the tire's impact on fuel economy and CO2 emission reductions. Tires with lower rolling resistance – and proper inflation pressure - can contribute to improved fuel economy.
In addition to the new fuel efficiency ratings, the proposal by the National Highway Traffic Safety Administration (NHTSA) also would provide consumers with two other key pieces of tire performance information - wet weather traction and tread wear. All three ratings would be prominently displayed on a removable label attached to the replacement tire at the point of sale.
The new, three-tiered ratings also will appear on safercar.gov to help consumers in compare ratings as they shop for new tires.
"Today's proposal takes the guess work out of buying the best tires for your vehicle," said U.S. Transportation Secretary Ray LaHood. "Our proposal would let consumers look at a single label and compare a tire's overall performance as it relates to fuel economy, safety and durability."
Tire sizes are listed on the side of your tire. Three of the most common sizing systems used today are explained below...
|Passenger Tires||Light Truck Tires|
P-Metric Sizing System
To accommodate the smaller tires used on compact cars, the P-Metric (Passenger Metric) system was created in 1976. The maximum inflation pressures of P-Metric tires were raised for lower rolling resistance. The P-Metric system is widely used by domestic tire manufacturers.
Light Truck Numeric System
Similar to the Numeric system for cars, it lists the section width in inches, construction type, rim diameter in inches, plus the light truck designation.
ISO Metric Sizing System
The International Standards Organization (ISO) Metric system combines the Metric system with a service description. The service description provides the load index along with the speed rating symbol.
Light Truck Metric Sizing System
Similar to the P-Metric system, except the P is replaced with the LT light truck designation. Also, LT-Metric and P-Metric tires differ in construction.
Light Truck High Flotation System
The same as the Light Truck Numeric system with tire diameter added to the front.