Below are some tire specific terms used when speaking about tires. These are common words in the tire industry, so we may use them not realizing that a customer may not be familiar with the term. If you ever have a question, please don’t hesitate to ask!
Adjustment – An allowance given to the customer to be used toward the replacement of a tire because of warranty or service issues.
Alignment – The checking and adjustment of camber, caster and toe angles of the vehicle’s suspension to maintain proper steering and handling of the vehicle for maximum performance.
Air Pressure – Force exerted by air within a tire, expressed in pounds per inch in USA and Bar in Europe.
Aspect Ratio -A numerical term which expresses the relationship between the standing height of the tire and the cross section width. (Aspect Ratio of 70 means the tire section stands approximately 70 percent as high as it is wide between the sidewall.)
Balance -The equal distribution of the mass of the tire and wheel assembly for smooth driving. Balance is achieved by fitting weights to the wheel rim to off-set uneven weight distribution of the tire, wheel or brake assembly.
Bead -The part of the tire that is shaped to fit the rim at the rim flange and the bead seat. Made of high tensile steel wires that are wrapped in woven fabric and then held by the plies and molded rubber. On clincher tires or (beaded edge tires) the bead is a hard rubber core reinforced by cord material in a specialized shape.
Bias Tires – Pneumatic tires having crossed layers of ply cord (usually two, four or more) running diagonally from bead to tread.
Bias Belted Tires – These tires have a body similar to that of bias tires, with the addition of two or more belts under the tread to strengthen and stabilize the tread. The belts improve tread life by reducing tread movement during contact with the road.
Camber – The measurement of tilt of the tire and wheel assembly on the front end of the vehicle off vertical measured in degrees.
Carbon Black – Substance used in tire manufacturing as a reinforcing material in the rubber mixing process which gives the rubber a higher resistance to premature wear.
Clincher tires – Early type of tire construction (as used on Ford Model T pre-1926). Clincher beads have a hard rubber core reinforced by cord material in a specialized shape with no steel in the bead. Air pressure is very critical to proper fitment of these tires. These tires are also referred to as Beaded Edge tires.
Contact Patch – The area of the tire that comes in contact with the road.
Cord – The twisted fiber or filament of polyester, rayon, nylon or steel which gives the tire body and belts strength.
Cross Section – The linear distance between the exterior sidewalls of an inflated tire at the maximum width.
Crown – The center area of a tire’s tread footprint.
Detachable Rim – Early style automobile rim permanently fixed to the wooden wheel. This type of rim has one or two side rings and possibly a separate lock ring to secure the tire assembly on the rim (see diagram on page 49 under Stanweld rim).
Demountable/Detachable Rim – Same as above except this rim removes from the wood wheel and is secured to the wood wheel by a series of lugs and lug bolts and clamp rings. (See diagram on page 49 under Stanweld rim)
DOT Number – Number molded onto the tire indicating the Manufacturer and date of manufacture as registered with the United States Department of Transportation. The final four numbers in the “DOT Code” indicate the date of manufacture, the first two numbers reflect the week and the last two indicate the year. So a tire stamped with 2915 was made in the 29th week of 2015.
Footprint – The area of the tire tread that is actual contact with the ground or road surface.
Drop Center – The drop portion of a rim cross section between the bead seats or rim flanges in which a bead is placed during the mounting process.
ECE Number – ECE (Economic Commission of Europe) developed testing standards for vehicles and tires which apply to dimensions, loads, tire markings and speed ratings.
ETRTO – European Tire and Rim Technical Organization.
Green Tire – A tire that has not yet gone through the process of vulcanization or curing in the tire molding process.
Gross Vehicle Weight – Total weight of a vehicle including all fluids, cargo and passengers.
Inner Liner – The layer of rubber which is laminated to the inside of a tubeless tire to insure the air retention quality of the tire body.
High Pressure Tire – 100 percent aspect ratio tire with cross section equaling section height. This type tire was used on example would be 35×5. The height of the tire should be 35 inches, the cross section should be 5 inches on a 25 inch rim.
Kilopascal – Metric unit for air pressure specifically in European use tires. One psi equals 6.9 kPa.
Load Carrying Capacity – Maximum load for which the tire is designed under standard conditions.
Load Index – Relative load carrying capacity as originated by European community, refers to the maximum load carrying capacity in kilograms and/or pounds.
Load Range – A system of designations, which identifies the carrying capacity range of a tire. These markings shown on the tire indicate the ply rating established for the tire such as B (4-Ply rating), C (6-Ply Rating) and D (8-Ply rating). This system was established by the Rubber Manufacturers Association.
Matched Slicks – Rear drag tires that when inflated to recommend PSI, have matching circumferences.
Matching Balance system – A computer balancing system used to match the high point of a rim to the low point of a tire diameter, creating a more perfecting round total assembly.
Maximum Inflation Pressure – The maximum air pressure in kpa/bar or psi that a tire can be inflated while cold. Usually found on sidewall of tire.
M+S – The designation of a tire that meets the requirements given by RMA to be used for all seasons.
NHTSA – National Highway Traffic Safety Administration (www.nhtsa.dot.gov).
Overall diameter – The diameter of an unloaded inflated tire, measured from the crown on one side to the crown on the opposite side. The free radius equals one-half the overall diameter.
Over-Inflation – The condition that exists when a tire is inflated beyond the pressure corresponding to the actual load or beyond the vehicle manufacturer’s recommendation.
P-Metric – A tire sizing system where the section width is shown in millimeters, the aspect ratio, type of construction and finally rim diameter are shown in inches example; (P205/75R15).
Plus One – From original equipment size tire and wheel, choosing to go up in rim diameter one inch while keeping the same overall diameter. Usually always adds width to rim and tire and decreases sidewall section height. Key is to keep same exact diameter to keep rolling circumference same.
Ply – A layer of rubber-coated parallel cords forming the tire body or carcass.
Polyester Cord – A synthetic fiber that excels in maintaining
strength properties at high heat levels, and eliminates flat spotting.
Post Inflation – When tires are removed from the mold after the curing process, they are mounted on a rim and inflated to their proper inflation, during the cooling period, to allow the tire to cool keeping its correct shape and size.
PSI – A measure of air pressure commonly used throughout the world signifying pounds per square inch.
RMA – Rubber Manufacturers Association. (www.rma.org).
Radial Ply – A tire with cords running radially from bead to bead (90 degrees to center-line of the tire). Radials have the addition of one or more belts under the tread to strengthen and stabilize the tread.
Radial Runout – Up and down movement of a tire and wheel assembly.
Rayon – A fiber used in tire construction made from cotton or wood pulp by chemical process.
Retread – A tire with the letter “R” before the three letter code indicates the tire as a retread. Performance Plus Tire does not sell retreaded tires!
Revolutions Per Mile – (R.P.M.) – The number of revolutions that the mounted tires will make in one mile, at rated load and inflation.
Ribs – Part of the tire tread design created by grooves running circumferentially around the tire.
Rolling Resistance – The resistance of a tire to free rolling.
Roll Out – Term used for drag tire circumference, and is the number of inches the tire rolls before it has traveled back to its initial starting point.
Section Height – The height of a tire measured from the rim to the outside measurement of the tread.
Section Width – Measurement of distance through cross sectional width of a tire at widest part, exclusive of scuffing rib when inflated to normal pressure and not under load.
Shoulder – The edge of a tire’s tread where the tread joins the sidewall.
Single Tube Tire – This is one of the earliest types of tire constructions as used on early automobiles, motorcycles and bicycles, where the tire and tube are made together and are fitted onto a rim with a semi-circle cross-section. The cord angles of the construction allow for the tire to tighten on the rim as it is inflated. These tires often have lugs for securing to the rim. They are often glued on the rims as well.
Sipe – To cut across a tire tread to produce biting traction edges. Also refers to the thin slots in the tread of a tire designed to aid in wet traction and water removal.
Speed Rating – A speed designation of S, T, H, V or Z shown in the size marking of some tires.
Synthetic Rubber – Rubber made by man using chemicals as opposed to natural rubber harvested from trees. Most tires today are made of this type rubber.
Tire Storage – Tires should be stored horizontally in a clean, dry place out of direct sunlight. White wall tires should never be stacked without something to protect the white wall.
UTQG – Universal Tire Quality Grade – A comparative figure of the tire that indicates treadwear, traction and temperature grade. Since this is a comparative figure and does not take into account vehicle, driving style or maintenance into account, the Treadwear rating cannot project actual tread mileage, nor can it be used to accurately compare projected tread life of one brand against another.