Load range
Load range: A letter-based strength classification for tires that groups them by maximum cold inflation pressure and load capacity.
Semi Truck Tire Glossary
Short definitions for tire terms that show up on sidewalls, work orders, inspection notes, and fleet policies.
Load index
Load index: A numeric code appearing in a tire's service description that corresponds to a specific maximum load capacity in a published table.
Ply rating
Ply rating: A historical shorthand for tire strength that originated in the era of bias-ply tires, where the number of actual cord plies determined...
Service description
Service description: The part of the sidewall marking that states load index, speed symbol, load range, and sometimes single or dual service...
Load and inflation table
Load and inflation table: A tire manufacturer's published chart showing the load capacity for a specific tire size and model at different cold...
GAWR
GAWR: Gross Axle Weight Rating — the maximum rated weight for a single axle system as set by the vehicle manufacturer, accounting for the combined...
GVWR
GVWR: Gross Vehicle Weight Rating — the maximum rated weight of the entire vehicle as certified by the manufacturer, covering the chassis, frame,...
Aspect ratio
Aspect ratio: The ratio of the tire's sidewall height to its section width, expressed as a percentage.
Section width
Section width: The distance between the outer sidewalls at the widest point of an inflated, unmounted tire, measured in millimeters on...
Overall diameter
Overall diameter: The outer diameter of an inflated, unloaded tire measured from tread surface to tread surface through the centerline.
Rim width
Rim width: The interior width of the wheel measured between the rim flanges where the tire beads seat.
Dual spacing
Dual spacing: The clearance relationship between two tires mounted side by side in a dual assembly, usually described by the distance between tire...
Steer tire
Steer tire: A tire mounted on the front steering axle of a tractor or truck — the position that directly controls steering response, handling...
Drive tire
Drive tire: A tire mounted on a powered drive axle — the axle or axles that receive torque from the driveshaft.
Trailer tire
Trailer tire: A tire mounted on a trailer axle — the rear axle or axles on the pulled unit rather than on the tractor.
Dual tire
Dual tire: One of two tires mounted side by side on the same wheel end, sharing the load of a drive or trailer axle position.
Single tire
Single tire: A tire used alone on a wheel end rather than paired with a second tire as a dual assembly.
Wide-base tire
Wide-base tire: A single wide tire that replaces a dual assembly at one wheel end, often called a wide-base single or super single.
Radial tire
Radial tire: A tire with casing cord plies running radially from bead to bead at roughly 90 degrees to the direction of travel, stabilized by belt...
Cold inflation pressure
Cold inflation pressure: Tire pressure measured before the vehicle has been driven more than one mile or after it has sat for at least three hours away...
TPMS
TPMS: Tire Pressure Monitoring System — an electronic system that monitors tire pressure in real time and alerts the driver when pressure drops below a...
Casing
Casing: The structural body of the tire beneath the tread rubber — comprising the radial cord plies, steel belt layers, bead wire bundles, and sidewall...
Tread depth
Tread depth: The depth of usable tread measured in the major tread grooves with a proper gauge.
Tread wear indicator
Tread wear indicator: A raised bar molded into major tread grooves at approximately 2/32 inch depth.
Sidewall
Sidewall: The flexible section of the tire between the tread shoulder and the bead — the area that compresses and rebounds under load with each revolution.
DOT date code
DOT date code: The last four digits of the Tire Identification Number — first two digits are the production week (01–52), last two are the year.
Tire Identification Number
Tire Identification Number: The full identifier molded into the tire sidewall beginning with "DOT." It includes the plant or manufacturer code, tire...
Valve stem
Valve stem: The inflation fitting through which a tubeless tire is filled, checked, and sealed.
Out-of-service
Out-of-service: An enforcement action requiring a commercial vehicle or driver to stop operating until a defect is corrected.
Zipper failure
Zipper failure: A sudden lateral sidewall rupture that can occur when a tubeless tire that was run flat or severely underinflated is reinflated.
Retread
Retread: A tire produced by inspecting a used casing, buffing its surface to a precise profile, optionally repairing damage that meets retreader...
Recap
Recap: Common trucking slang for a retread tire — both terms refer to the same product: a used casing that has been inspected, buffed, and retreaded...
Casing credit
Casing credit: A monetary credit a retreader or tire supplier applies toward a purchase in exchange for a returned casing that passes inspection.
Heat separation
Heat separation: A failure mode where tire layers, typically tread-to-belt or belt-to-belt, begin to come apart after excessive heat damages the...
Wheel end
Wheel end: The complete mechanical assembly at each wheel position, including hub, bearings, seals, spindle, wheel mounting hardware, and related brake...
Toe
Toe: An alignment angle describing how the front edges of a pair of tires point relative to the direction of travel.
Alignment
Alignment: The adjustment and measurement of wheel and axle angles, including toe, camber, caster, thrust angle, and axle tracking where applicable.
Rotation
Rotation: The practice of moving tires between axle positions or wheel positions to even out normal position-based wear.
Rolling resistance
Rolling resistance: The energy a tire consumes as it flexes and recovers while rolling under load.
Speed rating
Speed rating: A code indicating the maximum speed at which a tire is designed to carry its rated load over an extended period.
Void ratio
Void ratio: The proportion of the tread face that is open groove or void space compared with rubber contact area.
Bead
Bead: The reinforced edge of a tire that seals against the wheel rim flange and holds the tire in position.
Belt
Belt: Reinforcing layers of steel or other cord material located between the tread rubber and the radial casing plies.
Innerliner
Innerliner: The innermost layer of a tubeless tire — a specialized rubber compound that functions as the air barrier, replacing the inner tube used in...
Shoulder
Shoulder: The transition zone where the tread face meets the tire sidewall.
Tread rib
Tread rib: A continuous circumferential ridge of rubber on the tread face, defined by grooves on each side.
Tread groove
Tread groove: The open channel between tread ribs or lug blocks that channels water from the contact patch and contributes to wet-weather traction.
Sipe
Sipe: A narrow cut (typically less than 1.5 mm wide) made into a tread block or rib to add biting edges for wet, snowy, or icy traction.
Cord
Cord: The reinforcing fiber material — typically steel wire, nylon, polyester, or aramid — used to construct the structural layers of a tire.
Wheel rim
Wheel rim: The metal wheel assembly on which the tire is mounted.
Bead seat
Bead seat: The precision-machined surface on the wheel rim where the tire bead rests and seals.
Wheel runout
Wheel runout: The deviation from perfect roundness in a mounted tire and wheel assembly.
Wheel balance
Wheel balance: The even distribution of weight around the mounted tire and wheel assembly.
Inflation cage
Inflation cage: A safety restraint device required by OSHA (29 CFR 1910.177) when inflating tires that may have been run flat or that have unknown...
Axle weight
Axle weight: The actual measured load carried by a single axle at any given time.
Tandem axle
Tandem axle: Two drive axles mounted close together on a tractor, sharing the drive load.
Steer axle
Steer axle: The front axle that steers the vehicle.
Federal Bridge Formula
Federal Bridge Formula: A federal formula under 23 U.S.C.
Maximum inflation pressure
Maximum inflation pressure: The maximum cold inflation pressure at which a tire can be operated, molded on the tire sidewall.
Slow leak
Slow leak: A gradual loss of tire pressure that occurs over days or weeks rather than hours.
Valve core
Valve core: The small spring-loaded pin inside the valve stem that controls airflow.
Thermal pressure rise
Thermal pressure rise: The increase in tire pressure that occurs as the tire heats up during operation.
Flat spot
Flat spot: A localized area of reduced tread depth on one side of the circumference, caused by wheel lockup during braking, extended parking on a...
Cupping
Cupping: A wear pattern characterized by repeating scalloped dips or high-and-low spots around the tire circumference, usually caused by suspension...
Irregular wear
Irregular wear: Any tread wear pattern that does not progress evenly across the full tread width and circumference.
Cord exposure
Cord exposure: A condition where the structural fiber material beneath the tread rubber or inside the sidewall has become visible through the outer...
Sidewall bulge
Sidewall bulge: A localized outward protrusion of the tire sidewall caused by internal structural damage — broken cords, separated plies, or belt edge...
Ozone cracking
Ozone cracking: Surface cracking of the tire sidewall rubber caused by prolonged exposure to ozone, UV light, and weathering.
Tread separation
Tread separation: A failure mode where the tread rubber separates from the belt package or where belt layers separate from each other, typically...
CVSA
CVSA: The Commercial Vehicle Safety Alliance — an organization of enforcement agencies from the United States, Canada, and Mexico that establishes...
DVIR
DVIR: Driver Vehicle Inspection Report — a federally required document (49 CFR Part 396) that commercial drivers must complete at the end of each duty...
Dual matching
Dual matching: The practice of ensuring that two tires mounted in a dual assembly are closely matched in overall diameter, tread depth, and inflation...
Tread depth gauge
Tread depth gauge: A tool for measuring tread depth in major tread grooves.
Roadside inspection
Roadside inspection: An inspection of a commercial motor vehicle conducted at the roadside by authorized enforcement personnel, typically under DOT...
Highway service
Highway service: A tire application category for high-speed (55 mph or above), primarily Interstate or long-haul operation.
Regional service
Regional service: A tire application category for mixed highway and local operation — typically including city pickup and delivery, moderate highway...
Tire matching
Tire matching: The practice of ensuring that tires in dual assemblies — or across an axle — are matched by size, load range, tread depth, and in some...
Cost per mile
Cost per mile: A tire economics metric calculated as total tire cost divided by expected or actual removal mileage.
Fleet tire program
Fleet tire program: A managed system for purchasing, maintaining, tracking, and replacing tires across a commercial fleet.