Bias Ply Tire:
Bias Ply tires are constructed of layers of rubber-coated plies composed of textile cords placed upon each other at approximately 30-45 degree angles. These plies are then wrapped around the bead wires. As a result of a tire being bias in design it will have a circumference that varies from tire to tire. Because of its design a bias tire can expand due to increased air pressure or due to heat generated during use. This allows a team to tune their cars setup and stagger in order to help the car handle better. Bias-ply tires have many limitations. Since the plies were placed at angles to each other, the casing is subjected to strong friction due to inter-ply shearing, which builds up heat and increases tread wear due to a higher slip angle. The positioning of the plies also limits the tire’s ability to provide both superior handling and ride comfort. One big advantage of bias tire is the lower tire cost. Bias tires are also much more tolerant of the set up than radial tires. It is easier to set them up and they are typically easier to drive at the limit of traction. Bias ply tires like higher slip angles, in the area of 3°-5° and work best with less than 1 degree of camber.
Department of Transportation. Governing body that establishes regulations including tire labeling and performance standards of tires that are run inside the United States on public roads and highways.
A code molded into the sidewall of a tire signifying that the tire complies with U.S. Department of Transportation motor vehicle safety standards. The DOT code includes an alphanumeric designator, which can also identify the tire's manufacturer, production plant, and date of production and brand.
Used to refer to street-legal tires that can be purchased by the public, as opposed to racing tires. Many lower-cost forms of racing require use of Department of Transportation (DOT) tires
The portion or amount of area of the tread that contacts the road.
Refers to the number of times a tire is run up to operating temperature and then allowed to fully cool.
An assigned number ranging from 0 to 279 that corresponds to the load carrying capacity of a tire.
DOT required specification. Calculation based on pressure, construction and speed. The average load a tire can bear without damage under set specifications
Slang term for tires. Mostly used in drag racing.
Radial Ply Tire:
A type of tire that's constructed with the reinforcing belts sideways (bead to bead) under the tread rather than lengthwise. The cords in the body of a radial tire run at or near 90-degree angles to the centerline of the tread. The combination of stabilizing belts and the radial casing allows the tread and sidewall to act independently. The sidewall flexes easily under load and greater vertical deflection is achieved with radial tires. When negotiating curves and encountering side forces, the independent action of the tread and sidewalls keeps the tread flat on the road. This allows the tire to hold to its path. This results in better overall handling compared to a bias tire. Radials also run cooler than a bias ply tire because there is less friction between the plies inside the tire. But radials tend to demand a much more precise line around each track, whereas bias-ply tires are more forgiving. This is related to the slip angle that each design needs for maximum grip. Radial tires work best at 1-2 degrees of slip and need 2-3 degrees of camber. For the driver this translates into a bigger window of feedback to feel the tire working. The other related factor is the drop off in grip that occurs if the tire is pushed beyond the optimum. For bias ply tires, this tends to be a smooth transition that can be corrected, while with radial tires, the transition can be quite abrupt causing the car to loose control all at once. Radials are much more expensive to produce compared to bias tires.
The measured drag create by a driving surface, the tire, drive train parts, or a combination of all. The lower the rolling resistance, the less energy needed to keep a vehicle moving.
The circumference of an inflated tire. The measured distance a tire will cover in one revolution.
The changing of tires from front to rear or from side-to-side on a vehicle according to a set pattern; provides even tread wear.
The distance between to bead diameter and the outer diameter of the tire. This dimension is usually represented as a percentage of the tread width.
The width of the tire at the widest point when mounted on the correct rim. This is typically located somewhere about the midpoint of the sidewall.
That portion of a tire between the tread and the bead.
Racing tires having no tread design, in order to get the maximum amount of rubber in contact with the pavement.
Tire Identification Number. An alphanumeric code mark located usually on the sidewall of a tire to identify a manufacturing batch or date.
An assembly of rubber, chemicals, fabric and possibly metal, designed to provide traction, cushion road shock and carry a load under varying conditions.
An alphanumeric code molded into the sidewall of the tire that describes the tire's size, including width, aspect ratio, rim diameter, load index and speed rating. Most designations use the P-Metric system, although racing tires often use non-DOT nomenclature.
A metal or paper tag permanently affixed to a highway vehicle, which indicates the appropriate tire size and inflation pressures for the vehicle.
When a tire is coming in contact with part of the car.
The amount of laps or time run during the useful life of a set of tires.
When a racing series mandates that competitors can run only one "spec" or specified brand of tires. See "Spec."
A drag racing phenomenon when a loss of traction and/or tire distortion causes the tires to shake violently. Normally, the car becomes out of control and the driver's vision is blurred from the movement. See also back-pedaling.
A solvent, which is applied to the surface of tires, changes the chemical characteristics of the tread rubber. Sanctioning bodies and most weekly tracks have banned the use of tire softeners because they are based on aromatic hydrocarbons (such as benzene or xylene), which are toxic with repeated exposure. They may also cause damage to the structure of the tire and increase the risk of failure.
The amount of laps or time run during the useful life of a set of tires.
The loss of rubber from tire treads due to use.
The portion of a tire that comes into contact with the road.
The usable thickness of the tread. Small pinholes, called depth holes, are placed in the tread so tread depth can be measured.
This refers to the groove design on the operating surface of a tire. Most patterns are molded into the tread at the factory, but a custom grooved tire is also said to have a tread pattern.
The tread section that runs around the circumference of the tire separated by the tread grooves.
The width of a tire's tread.
Tread Wear Indicator: Narrow bands, sometimes called "wear bars," that appear across the tread of the tire when only 2/32 inch of treads remains. This applies to DOT type tires.
A hopping action of the rear wheels during heavy acceleration. Traction is lost and regained in rapid cycles after power is applied to the rear wheels.