pressure: Force exerted by air
within a tire, expressed in pounds per square inch or kilopascals.
Aspect ratio: The dimensional relationship between tire section height
and section width; section height divided by section width.
Bead: The area of the mounted tire which seats against the wheel.
Bead filler: A rubber extrusion in the bead area of a tire; used to
permit a smooth contour of casing plies around the bead and to the lower
sidewall. Also used in enlarged form to stiffen the lower sidewall of a tire.
Bead seat: The position where the tire rests and seals on the
inside of the rim.
Belted bias tire: A bias tire with additional reinforcing belt(s) between
the casing plies and the tread.
Bias tire: A tire built with two or more casing plies which cross
each other in the crown at an angle of 30 or 45 degrees to the tread
Body: Tire structure except for tread and sidewall rubber.
Bulge: Acceptable section repair in a radial tire not to exceed 3/8"
(9.6mm) in height. This "bulge" may be identified by a blue
Cap and casing: A commercial truck tire that has been retreaded; usually
bought as an emergency replacement.
Carcass: The body of a tire; another term for casing.
Casing: The main body of a tire; includes the sidewall, steel belts (if
applicable), and surface underneath the tread of a tire.
Cold inflation: The pressure in a tire that has been driven less than 1
mile or has been standing for three hours or more.
Compounding: Refers to the mixture of ingredients that go into the
rubber used in a tire. Different chemicals or types of compounds affect wear,
traction, cut resistance or other properties of a tire.
Cross section width: External sidewall to sidewall measurement of inflated
tire, exclusive of ornamental ribs and lettering. Sometimes called section
Crown: The region between the shoulders of the tire.
Cure: To vulcanize; also time and temperature conditions used to vulcanize a
Custom retreading: The service provided when used tires are brought to a
technician for retreading.
DOT: A tire branding symbol which denotes the tire meets requirements of the
Department of Transportation.
Drive position: Axle providing steering power to the vehicle (i.e., front
Duals: Two tire and wheel assemblies, mounted on one side of an axle.
Dual position: Tandem wheels, such as on a tractor-trailer.
Durometer: A measure of the hardness of a rubber compound; its
resistance to penetration of a spring-loaded blunt needle.
ETRTO: European Tire and Rim Technical Organization.
Footprint: The mark left by a loaded tire's tread as it comes in
contact with the road surface.
Green tire: A tire which has not been vulcanized or cured.
Grooves: Circumferential channels between the tread ribs of a tire.
Gross Vehicle Weight (GVW): The total weight of the vehicle, including
passengers, fuel, cargo and attachments.
Gross Vehicle Weight Rating (GVWR): The maximum permissible loaded weight
of the vehicle and takes into account the capabilities of the engine,
transmission, frame, spring, brakes, axles and tires. The GVW must not exceed
H-Rated: A speed rating category for tires which is used on
vehicles with a top speed up to 130 mph.
Innerliner: The layers of low permeability rubber which are
laminated to the inside of a tubeless tire to insure the air retention quality
of the tire body.
Load-carrying capacity: the load a particular size tire can carry at
a given inflation pressure under certain driving conditions, as established by
the Tire and Rim Association.
Lock Ring: The third piece of a 3-piece rim assembly which locks
the side ring to the rim base.
Lower sidewall: The part of the sidewall nearest the bead.
LT-Metric: A sizing system using the section width in millimeters,
aspect ratio, type of construction and rim diameters in inches (e.g.:
LTP-Metric: A new (1992) light truck personal use sizing systems
using the section width in millimeters, aspect ratio, type of construction and
rim diameters in inches (e.g.: LTP235/75R15).
M+S, M/S or M&S: a tire sidewall designation indicating that the tire
meets the RMA definition of a mud and snow tire.
Metric Tire Size System: A tire sizing system using the cross section
in millimeters, aspect ratio, speed category, tire construction and the rim
diameter in inches (e.g.185/70SR13).
Multi-Piece Rim Assembly: A rim consisting of more than one part.
Usually two pieces (rim base, and side ring) or three pieces (rim base, side
ring and lock ring) for use with tube type tires.
NHTSA: National Highway Traffic Safety Administration.
Overinflation: The inflation of a tire above recommended pressure to
achieve improved performance; negative byproducts are rough ride, bruise damage
and suspension system strain.
P-Metric System: A tire sizing system using the section
width in millimeters, aspect ratio, type of tire construction and rim diameter
in inches (e.g.: P225/70R15).
Plies: The layers of fabric that make up the cord body of a tire.
Polymer: A chemical compound made up of a large number of identical components
linked together like a chain.
PSI: Pounds per square inch.
Pull stage: The recommended end of a tire tread's useful life;
measured in 32nds of an inch deep.
Radial tire: A tire built with casing plies that cross the crown at
an angle of 90 degrees.
Recap: Another term for a retreaded tire.
Retread: A used casing which has new tread rubber applied to it.
Ribs: The rubber elements at the tire tread which contact the ground,
oriented in a generally circumferential direction.
Rim: The component that supports the tire and contains the inflation
pressure. It may be single piece or multi-piece.
RMA: Rubber Manufacturers Association.
S-Rated: A speed rating category for vehicles with a top speed up to 112 mph.
Section height: the distance from the bottom of the bead to the top of
Section width: The distance from sidewall to sidewall, exclusive of any
Shoulder: Outer edges of tire tread.
Sidewall: The portion of a tire between the
thread shoulder and the rim bead.
Sipes: Small, narrow
slots molded into the ribs of the tread design which increases the traction
edges of the tire and increases the traction ability of the tire on wet
Speed rating system (Speed Category Markings): An alphabetical
system describing a tire's capability to travel at established and
Steel Belt: A belt material used in tires. Its high stiffness
provides good handling and low tread wear.
Steer position: Front tires that actually steer the vehicle.
TIA: ITRA (International Tire & Rubber
Association) and TANA (Tire
Association of North America) merged into one organization TIA (Tire Industry Association) on
July 1, 2002.
T-Rated: A speed rating category for vehicles with a top speed up to 118 mph.
Top Cap Treading: Only the top or tread (crown) area is buffed and a tread
rubber with abrupt shoulder applied. This type of treading is used mostly on
truck tires in highway service where appearance is not as important as economy.
Trail position: Axle not providing steering power to the vehicle
Tread: The grooved or patterned exterior part of the tire which contacts the
Tread buffing: A process in which a portion of the tire tread is
removed by buffing or grinding it down: similar to tread shaving.
Tread depth: The distance measured near the centerline of the tire,
from the base of the tread design to the top of the tread.
Tread grooves: The space between two adjacent tread ribs, lugs or bars.
Tread life: Length of service in miles before the tread wears out.
Tread radius: The radius of curvature of the tread arc across the
Tread rib: A tread section running circumferentially around a tire.
Tread rubber: Compounded natural or synthetic rubber that is placed on
a buffed casing and vulcanized to produce a new wear surface.
TRMG: Tread Rubber Manufacturers Group.
Tread wear indicators: Narrow bars of rubber molded at a height of
2/32" (1.6mm) across the bottom of the tread grooves. When the tread wears
to these bars, the tire should be replaced.
Tread width: The tread width is the distance from outer edge to outer
edge of the tread.
Underinflation: A tire having less than recommended air pressure for the
load carried. The tire could build up excessive heat that may be dangerous and
result in sudden tire destruction.
Undertread: The rubber between the base of the tread and the tire
Undulation: A slight indentation or wavy appearance on the sidewall
surface of an inflated radial tire. Radial body ply cords run straight across
the tire from bead to bead and the joining of the ply material in the sidewall
area may sometimes cause this condition. Undulating is a common characteristic
of radial tires and will not effect the performance of the tire.
Valve Stem: The tube through which air flows in or out of a tube or
Variable Integrated Pitch: Variations in angles and sizes of a tire's
tread elements that reduce ride noise levels.
Veneering: Application of a thin layer of rubber materials used in
bead-to-bead retreading to cover the prepared sidewall.
V-rated: A speed category for vehicles with a top speed of more than 130 mph.
Load index V-speed rated capped at 149 mph.
Vulcanization: The linking together, under heat and pressure, of rubber
compound polymers which changes material from a sticky, putty-like substance to
an elastic, bouncy substance.
Wide Oval Tire: One which has an aspect ratio lower than 75. The Wide
Oval design has several advantages other than striking appearance, such as
greater handling stability.
Z-Rated: A speed category for a vehicle of a top speed of more than 149 mph.
Zero Offset: A condition where the centerline of the wheel coincides
exactly with the mounting face.
Zipper Rupture: The steel cords that extend bead-to-bead become damaged
and weaken from running the tire underinflated causing a rupture to occur in
the sidewall flex area of steel radial tires releasing a tremendous force of
air pressure. This serious subject is discussed, in depth, under Tires from
A-Z. If you repair tires, please take the time to become informed.