Tire & Vehicle Dictionary


This dictionary was compiled from several sources across the tire, vehicle service, commercial trucking, retreading and OTR equipment markets.

FABRIC – An array of parallel cords used in tire manufacturing.

FABRIC FATIGUE – Fabric degradation and resultant tire cord breakdown due to repeated flexing and heat.

FIBERGLASS – A material used in belt construction, consisting of fine spun glass coated with adhesive. Preferred spelling is fiberglas.

FIFTH WHEEL – Coupling device attached to a tractor or dolly that supports the front of a semi trailer and locks it to the tractor or dolly. The fifth wheel’s center is designed to accept a trailer’s kingpin, around which the trailer and tract or on dolly pivot in turns.

FILLER STRIP – Free flowing rubber used under the tread when added thickness is needed.

FIXED TANDEM – Assembly of two axles and suspension that is attached to the chassis in one place, and cannot be moved fore and aft.

FLANGE – Curved metal extremes of a rim that retain the tire on the rim base.

FLANGE HEIGHT – Measured from top of flange to bead seat, and is the difference between overall diameter and nominal rim diameter, divided by two.

FLANGE SEAL/L-RING/O-RING – An L- or O-shaped rubber seal used in some tubeless OTR tire mountings to prevent air loss between the tire beads and the flange and rim base, and flange and loose taper seat.

FLAP – Rubber protector used in tube type truck tires to prevent injury to the tube by the bead toes and at the valve slot of the rim.

FLAT BASE – In common usage, it applies to any truck rim not having a center depression. A demountable flange (consisting of one- or two-piece side/lock ring) permits the removal of the tire and holds it in place after installation.

FLAT SPOT – Irregular wear in an isolated spot or spots around the tire tread.

FLIPPER STRIP – Another name for a ply turnup in new tire manufacturing.

FLOTATION – Generally referring to large low pressure tires, the ability of a tire to pass over soft surfaces without sinking in. 

FLOTATION TIRE – Tire designed to minimize soil penetration and compaction.

FLUSH FIT – Condition where the mounting pad of the wheel goes into place freely and without obstruction against the hub-mounting surface.

FOLLOWER JOINT – Non-load-carrying ball joint that maintains the position of the steering knuckle and provides the correct steering axis inclination angle; sometimes called pilot joint or friction joint.

FOOT POUND – One pound of force at the end of a one foot long lever; a measurement of torque i.e., 3ft. bar x 150 lbs. = 450 foot pounds).

FOOTPRINT – The mark left by a loaded tire's tread as it comes in contact with the road surface.

FOOTPRINT AREA – Area of contact in square inches the tire has with the road. This is dependent upon both load and inflation pressure, as well as tire dimensions.

FORE-AND-AFT WEIGHT TRANSFER – Load factor where weight is transferred from the front tires to the rear tires during acceleration and from the rear to the front tires during braking.

FOR-HIRE CARRIER – Company in the business of transporting freight belonging to others.

FORK LIFT/LIFT TRUCK – Machine having metal arms extended in front for picking up and moving pallets or skids.

FRAME – Backbone structure around which the vehicle is assembled.

FREE RADIUS – Measurement in inches from the wheel axle centerline to the top of the tire when inflated. The radius that is not under load.

FREE ROLLING WHEEL – Non-powered wheel position on a vehicle, such as steering axle, tag axle or trailer wheel positions.

FILLER – Material used to fill the area above the bead between the outer and inner portion of the sidewall. Also used in enlarged form to stiffen the lower sidewall of a tire.

FRICTION – Force between the tires and the road surface which causes the tire to grip the road.

FRONT WHEEL INDEPENDENT/DEAD REAR – Suspension system found only on front wheel drive cars. It has a solid rear axle that does not transmit driving torque since the car has front wheel drive. It just holds up the rear wheels.

FRONT WHEEL INDEPENDENT/LIVE REAR – Suspension system found only on rear wheel drive cars. The rear wheels are connected together through an axle that is in turn connected to the frame. A live rear axle includes the differential and transmits driving torque through itself to the rear wheels.

FULL CAP – New tread rubber added to the buffed casing, covering the crown and shoulder areas.

G – Unit of acceleration. "g" is a symbol that represents the acceleration of gravity. Acceleration at 1g equals 32 feet per second.

GEAR RATIO – Number of revolutions of a driving gear required to turn a driven gear through one full revolution. For a pair of gears the ratio is found by dividing the number of teeth on the driven gear by the number of teeth on the driving gear. Changing tire size will change the effective gear ratio. An increase in loaded radius will increase ratio, increase speed and reduce power.

GEARED SPEED – Calculated vehicle speed at the engine's governed rpm in each transmission gear, or (commonly) in top gear.

GLAD HANDS – Separable mechanical connector used to join airline hoses when combination vehicles are coupled together.

GRADE – Steepness of a grade, expressed as a percentage. Example: A vehicle climbing a 5% grade rises five feet for every 100 feet of forward travel.

GRADEABILITY – Vehicle’s ability to climb a grade at a given speed. Example: A truck with a gradeability of 5% at 60 mph can maintain 60 mph on a grade with a rise of 5%.

GREEN TIRE – Tire which has not been vulcanized or cured.

GROOVE – Circumferential channels between the tread ribs of a tire. Either angled or circumferential, grooves are voids that promote water channeling. Grooves the most efficient means of channeling water from in front of to behind the tire. By designing grooves circumferentially, water has less distance to be channeled. Circumferential grooves provide the shortest distance from the front to the rear edges of the contact patch. Lateral and angled grooves help break up the wedge of water that forms at higher speeds, reducing the chance of hydroplaning and increasing tire contact with the road.

GROOVE CRACKS – Splitting or cracking of the rubber (undertread) at the base of the grooves, between tread ribs. Primarily caused by growth in textile casings.

GROOVING – Tread cutting process in which grooves of varying depths and angles are cut into a tire's tread to improve forward traction, braking, or lateral stability.

GROSS AXLE WEIGHT RATING (GAWR) – Maximum weight that the front or rear axle can carry. The front and rear gross axle weight must not exceed the front and rear GAWRs.

GROSS COMBINATION WEIGHT RATING (GCWR) – Total weight of the loaded tow vehicle and the loaded trailer.

GROSS VEHICLE WEIGHT (GVW) – Total weight of the vehicle, including passengers, fuel, cargo and attachments.

GROSS VEHICLE WEIGHT RATING (GVWR) – 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 the GVWR.

GROWTH/TIRE GROWTH – Stretching of textile tire cord materials due to heat and loss of strength, resulting in the casing increasing in size.

GUM STOCK/CUSHION GUM – Rubber compounds containing only the necessary ingredients for vulcanizing. Reinforcing fillers are not present in gum stock.

GUTTER – The recessed area on a truck rim base that holds the lock ring in place.

28° GUTTER BEVEL – Truck rims are beveled to provide for the gutter and this bevel matches a 28° taper at the inside of the cast spokes, holding the rim in place.

HAZMAT – Hazardous materials, as classified by the U.S. Environmental Protection Agency (EPA). The U.S. Department of Transportation strictly regulates transport of hazardous materials.

HEADACHE RACK – Heavy protective barrier mounted behind the tractor's cab. Designed to prevent problems caused by load shifting forward from the trailer and crushing the cab.

HEEL & TOE WEAR – Uneven wear of tread blocks on a tire. The trailing edge of the block often tends to wear at a faster rate that the leading edge.

HELPER SPRING – Additional spring device permitting greater load on axle.

HIGH FLOTATION SIZING SYSTEM FOR LIGHT TRUCKS – System using overall diameter in inches, section width in inches, type of tire construction, and rim diameter in inches (e.g.: 33x12.50R15LT).

HIGH PRESSURE DIE CAST – Wheel manufacturing process using aluminum, alloys in special high-pressure die casting machines.

HIGHWAY TIRES – Also called summer tires as they are designed for wet-and-dry weather driving, but not for use on snow and ice.

HORSEPOWER (HP) – Measure of power referring to the amount of work that can be done over a given amount of time. One horsepower is defined as 33,000 foot-pounds of work in one minute. Example: Lifting 33,000 pounds one foot in one minute, or lifting 3,300 pounds 10 feet in one minute.

HOT CAP – An incorrect term referring to mold cure retreading. Mold cure retreading is a method in which uncured rubber is added to a buffed casing and cured in the mold at temperatures of approximately 290°-300°. This temperature allows uncured rubber to flow in the matrix forming the tread design during vulcanization.

HOURS-OF-SERVICE – U.S. Department of Transportation safety regulations which govern the hours of service of commercial vehicle drivers engaged in interstate trucking operations.

HUB – Base of an axle end, having studs protruding from its face upon which the wheel is mounted to the vehicle.

HUB CENTRIC – Situation where the center bore hole of a wheel is made to match up with the hub diameter of the vehicle; the wheel is then centered by the center hole, rather than the lug nuts.

HUBODOMETER – Register showing miles traveled by vehicle mounted directly on the axle hub. Popular means to record mileage for leasing of vehicles or tires particularly on trailers, since there is no other odometer present.

HYDROPLANING – Loss of traction at high speeds caused by a wedge of water, which lifts a tire off the road surface. Also known as aquaplaning.

HYDROSTATICALLY INFLATE – To inflate with water in place of air. HYDROPLANING – Loss of road contact due to the buildup of water: between tire tread and road surface. It occurs when factors, including speed, water depth, tread depth and inflation pressure, so combine that lifting force is exerted under the tire.

HYSTERESIS – The energy lost and not returned, when tire materials are subjected to stress in any direction. Lost energy is converted to heat through molecular interaction, and since rubber has poor thermal conductivity, internal temperatures of a tire can build up rapidly under repeated flexing.

IDLER ARM – Device attached to the frame of the car that duplicates the movement of the Pitman arm and keeps the center link aligned.

IMBALANCE – Non-uniform distribution of mass in a tire and wheel assembly about its axis of rotation.

IMPACT BREAK – Rupture to a tire resulting from shock of striking a chuckhole, rock curb, etc. and not caused by cutting.

INCLUDED ANGLE – On a truck, the sum of the camber and kingpin inclination angles. This angle is designed into the steering knuckle and must remain constant.

INDEPENDENT SUSPENSION – Suspension system in which the front or rear pair of wheels of a car are independently connected to the frame or underbody. In this system, deflection of the wheel on one side will not affect the wheel on the other side.

INDUSTRIAL SOLIDS – Non-pneumatic tires, often used on forklifts where flats are a constant problem.

INERTIA – Tendency of any mass at rest to stay motionless, or any mass which is moving to remain moving in a straight-line.

INNERLINER – Layers of low permeability rubber that are laminated to the inside of a tubeless tire to ensure the air retention quality of the tire body.

INNER TUBE – Tire-shaped rubber air chamber, containing a valve and placed inside the tire casing. It seals in the air, which supports the load, but is not capable of supporting the load without the strength of a tire and rim surrounding it.

INSIDE CURING RIM – Metal support for a retreading curing tube that fits inside a tire.

INTER-AXLE DIFFERENTIAL – Gear device equally dividing power between axles and compensates for unequal tire diameters.

ISO METRIC SIZING SYSTEM – International Standards Organization (ISO) metric tire sizing system combines the metric system with a service description. The service description provides the load index along with the speed-rating symbol.

ITRA – International Tire & Rubber Association.

JACK – Mechanical, hydraulic, or pneumatic lifting device to raise chassis for repairs or tire changes.

JACKKNIFING – Occurs when the trailer over-comes the tractor, pushing the tractor drive wheels sideways, forcing the combination into a V-shaped attitude, resulting in a complete loss of control with no possibility of recovery.

JAKE BRAKE – See Engine Brake.

KETTLE – Curing method (new or retreaded) using an autoclave that uses steam and air to create the heat and pressure needed to vulcanize tire rubber.

KILOPASCALS (KPA) – Unit of air pressure; in metric terms it takes 6.89 kPa to equal 1 psi.

KINETIC BALANCE – See Balance.

KISSING BETWEEN DUALS – Intermittent contact of tires in dual as they flex, caused by inadequate dual spacing or by overload.

KINGPIN – In referring to an axle, it is the pin around which a steer axle’s wheels pivot. In referring to a trailer, it is the anchor pin at the center of a semi trailer’s upper coupler, which is captured by the locking jaws of a tractor's fifth wheel to attach the tractor to the semi trailer.

KINKED BEAD – Sharp, permanent bend in bead wire at one or more points around the circumference of the bead.

LADEN WEIGHT – See Gross Vehicle Weight.

LADING – Load or the freight in a vehicle

LANDING GEAR – Retracting legs that support the front of a semi trailer when it is not coupled to a tractor.

LATERAL CLEARANCE – Smallest distance laterally between the tire and the nearest fixed point of the vehicle.

LATERAL RUN-OUT – Tire/wheel assembly that does not run true to its plane, such as a damaged wheel moving in a wobbling, side-to-side manner.

LATERAL STABILITY – Limiting side movement. Tread grooves running circumferentially around the tire resist side forces for maximum traction on turns. Also, stabilizing tread plies limit side-to-side movement of the tread ribs caused by the expansion and contraction of tread areas as sidewalls flex.

LATERAL WEIGHT TRANSFER – Load factor in cornering where weight is transferred from the inside tires to the outside tires.

LCV/LONG COMBINATION VEHICLE – In general, vehicles longer than a standard doubles rig, which consists of a tractor and two 28-foot semi trailers. Examples of LCVs that are permitted in some U.S. western states and eastern toll roads: Twin 48-foot trailers, triple 28-foot trailers.

LEAD – Slight pull to one side.

LEAF SPRINGS – Series of steel leaves used on suspension systems that are bolted together in the middle. Under compression, they flatten and expand in length, then rebound to their original arched shape.

LIFT AXLE – Extra, unpowered axle needed only when the vehicle is loaded, allowing it to meet federal and state vehicle weight standards. The lift axle is mounted to an air spring suspension that raises the axle when it is not required.

LIFT POINTS – Contact point on the chassis of a vehicle used to hoist the vehicle for servicing; to prevent serious problems and permanent damage, owners' manuals should always be checked for proper lift point locations.

LIGHT TRUCK HIGH FLOTATION SYSTEM – Tire sizing system that is the same as the Light Truck Numeric System with tire diameter added to the front. It lists the section width in inches, construction type, rim diameter in inches, plus the light truck designation.

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.

LINEARITY – Ability of a vehicle to respond linearly to the driver’s steering input at low cornering levels.

LIQUID BALLAST – Liquid solution, usually calcium chloride, put inside a tire as a means to add unsprung weight. Usually used in agricultural or OTR equipment applications.

LIVE AXLE – The drive axle on a vehicle.

LOAD BASE – Used in calculating load distribution, it is the distance between the center of the rear axle (or center between tandem axles) and the center of payload. Negative load base occurs when the payload is behind the rear axle, taking load off the front axle.

LOAD DISTRIBUTION – Distribution of load on truck or trailer chassis, or the relationship of the gross load on the front and rear axles to the total gross load.

LOAD DISTRIBUTION CALCULATION – Payload on the front axle is equal to the total payload multiplied by the load base (in inches) and divided by the wheelbase (in inches). Formula: PLFA = PL x LB/WB. To complete the calculation of load per axle, it is necessary to obtain the unladen weight of the vehicle and estimate its breakdown by axle.

LOAD INDEX – Numerical code that specifies the maximum load a tire can carry at the speed indicated by its speed symbol, at maximum inflation pressure.

LOAD & INFLATION TABLE – Chart in the tire manufacturer’s databook listing the carrying capacity of a tire at each of several air pressure increments from the lowest range of practical use to its maximum capacity.

LOAD RANGE – Replaces the former ply rating term and identifies load and inflation limits.

LOAD RATING – Weight that a wheel is designed to support in normal service.

LOAD RATING/LOAD RANGE – Method of rating a tire’s load-carrying capacity (denoted by letters such as B, C, D, etc.) with respect to its ply rating.

LOAD-CARRYING CAPACITY – Load a particular size tire can carry at a given inflation pressure under certain driving conditions, as established by the Tire and Rim Association.

LOAD TRANSFERENCE – Changing of the amount of load distributed to each axle while the vehicle is in motion, due to the effects of braking, cornering, ascending, or descending grades, etc. Also know as rollster.

LOADED RADIUS/STATIC LOADED RADIUS – Measurement in inches from the wheel axle centerline to the ground when the tire is properly inflated for the load.

LOADED SECTION HEIGHT – Height of the section of the tire that is making contact with the road.

LOADING – Amount of weight put on tires. Increased load can increase cornering force.

LOCK RING – Metal ring which snaps into the rim gutter, holding the side ring in place.

LOGBOOK – Book carried by truck drivers in which they record their hours of service and duty status for each 24-hour period. Required in interstate commercial trucking by the U.S. Department of Transportation.

LONG TON/GROSS TON – Equal to 2,240 pounds.

LOPING/ROAD LOPING – Term used to describe bouncing in OTR and agricultural equipment, caused by natural vibration and intensified by the tires. Considered a driver comfort issue, though severe loping can impact work.

LOW BED/LOW BOY – Low platform trailer for heavy equipment hauling, usually on 15-inch diameter tires.

LOW PRESSURE TIRES – Larger cross-section tires for operation at lower pressure. Increased air capacity permits lower pressure.

LOW PRESSURE INDICATOR – Unit or combination of units which provides a visible or audible warning signal whenever a tire’s air pressure is below a predetermined value.

LOW PROFILE – Refers to the aspect ratio of a tire where the section height is smaller than section width.

LOWER SIDEWALL – Part of the sidewall nearest the bead.

LOW TEMPERATURE GUM – Rubber compound which cures at a lower than standard temperature.

LTL/LESS-THAN-TRUCKLOAD – A quantity of freight less than that required for the application of a truckload (TL) rate, usually less than 10,000 pounds.

LTL CARRIER – Trucking company which consolidates less-than-truckload cargo for multiple destinations on one vehicle.

LT-METRIC – 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. System uses the section width in millimeters, aspect ratio, type of construction, and rim diameters in inches (e.g.: LT235/85R16).

LTP-METRIC – Newer (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).

LUG – A discontinuous tread element.

LUG CENTRIC – Centering of a wheel by matching it up with the lug nuts, rather than by the center bore hole of the wheel; hub centric is the more accurate centering method.

LUG TEARING – A rupture or rip of a tread lug.

"M" DIAMETER – Diameter at the base of a tread design, or the matrix undertread diameter.

M+S/M&S – Tire sidewall designation indicating that the tire meets the RMA definition of a mud and snow tire.

MACPHERSON STRUT – Front suspension assembly that combines the functions of the shock absorber, the upper steering pivot, and the wheel spindle in a single unit.

MAG – Misleading description of specialty wheels; with exception of pure racing wheels, as specialty wheels contain little or no magnesium.

MANDREL – Curved support inserted into a tire during retread processing to prevent the casing from collapsing while building tread or curing a repair.

MASTERBATCH – Homogenous mixture of rubber and other materials for use as a raw material to produce a tread compound.

MATCH MOUNTING – Mounting procedure that matches the high point of a tire with the low point of its wheel. A dot or mark on the tire is matched with a dot, a sticker, or the valve hole on the wheel.

MATRIX/MATRICES – Aluminum or steel rings or segments which form the cavity in which a tire (new or retreaded) is actually cured, and from which the tread pattern is formed.

MATRIX SKIRT – A portion of the matrix that supports the tire sidewall during curing.

MATRIX UNDERTREAD DIAMETER (MUD) – In retreading, the ideal buffed diameter for a casing to be cured in a specific matrix.

MAXIMUM INFLATION PRESSURE – Maximum air pressure, to which a cold tire may be inflated, this figure (in psi and kPa) is molded onto the sidewall of a tire.

METRIC TIRE SIZE SYSTEM – Tire sizing system, originating in Europe, using the cross section in millimeters, aspect ratio, speed category, tire construction and the rim diameter in inches (e.g.: 185/70SR13).

MILL – Device used in retreading consisting of two rotating rolls used to warm, mix and blend rubber compounds.

MILLING – Process of breaking down raw rubber and blending it with curative ingredients and other compounds.

MILLIMETRIC SIZING SYSTEM – Similar to the Metric system except that the rim diameter is also represented in millimeters.

MODULUS – Term used to measure cured rubber’s resistance to a 300% stretching.

MOISTURE BLOWS – Ply separations caused by moisture in the casing, which when subjected to heat, becomes steam and expands.

MOLD – Equipment that impresses the tread pattern into uncured tread rubber as it vulcanizes the new tread (in retreading) or the entire tire (new tire).

MOLD CURE – Retreading process by which uncured tread rubber is adhered to the casing and vulcanized by use of steel or aluminum molds, which impress a tread pattern into the tread compound while curing.

MOLD VENTS – Thin, string-like strands of cured rubber on a new tire, the result of rubber compounds that filled venting holes in the mold during vulcanization.

MOLDING SHRINKAGE – Shrinkage in rubber gauge as uncured rubber is vulcanized, usually with the 2% to 3% range.

MOUNTING PAD – Surface area of the back of the wheel’s center that contacts the brake drum or hub flange of the vehicle.

MOUNTING DIAMETER – To find this measurement, subtract the total rim drop – multiply the rim drop from one side by 2 – from the overall diameter of the wheel. Example: 0.75 inch rim drop X 2 = 1.5 inches. If the overall diameter is 18 inches, the mounting diameter is 18 – 1.5 = 16.5 inches.

MULTI-PIECE REPAIR – Also commonly called a "patch and plug" repair as such a tire repair utilizes a vulcanized repair stem or plug and a reinforced patch to fill a tire injury and reinforce the injured area.

NATURAL RUBBER – Elastomer produced from latex, a milky sap obtained from the rubber tree. An elastic and. porous form of rubber.

NEGATIVE CAMBER – Condition where the top of the tire is leaning inward from the tire’s vertical centerline, as viewed from the top.

NEGATIVE CASTER – Setting where the steering axis is inclined forward at the top as viewed from the side; a condition which tends to cause instability.

NEGATIVE OFFSET – When the back of the bolt pad is closer to the inside of the wheel; when the mounting face at inboard of the rim centerline extends assembly away from vehicle resulting in wider tracking.

NHTSA – National Highway Traffic Safety Administration.

NIBBLING – Jerking action that occurs in a vehicle, due to the distortion within some tires as they are forced to traverse pavement ridges at a slight angle.

NOMINAL – Tire dimensions figured from the actual numbers in the size.

NOMINAL RIM DIAMETER – Diameter of a tire rim, bead seat to bead seat 180° opposite, given in nearest whole numbers (e.g. 15-inch)

NOMINAL WlDTH – Rim measurement Measured between the flanges at the bead seat.

NON-DESTRUCTIVE TESTING/NDT – A method of testing or examining a tire casing during the retreading process in such a way as to not hurt the integrity of the casing. Commonly called "NDT," such testing can be done by x-ray, sonar, electric current or various other methods.

NON-DIRECTIONAL TREAD – Arrangement of bars, grooves and ribs in and) manner that gives equal traction in forward or; reverse direction.

NUMERIC SIZING SYSTEM – First system developed for tire sizing was used until the late 1960s, but provided only the cross section width of the tire and the rim diameter in inches. If the section width ended in zero (e.g., 7.00-14 or 7.50-14), the tire had a common aspect ratio of about 92. For section widths not ending in zero (e.g., 8.25-15), the tire was considered "low profile" with an aspect ratio of about 82.

NYLON – Synthetic fiber.

ODOMETER – A register showing miles driven by a vehicle, usually located in the speedometer.

OE/ORIGINAL EQUIPMENT – Refers to tires or other components sold to automobile, truck or heavy equipment manufacturers to equip their new vehicles.

OEM/ORIGINAL EQUIPMENT MANUFACTURER – This term refers to the primary vehicle manufacturer or any secondary manufacturers that produce components for new vehicles.

OFF-ROAD – Term generally used to describe passenger, light truck/SUV or medium/heavy truck tires that are used on surfaces other than pavement.

OFFSET – Distance from the centerline to the mounting face of a wheel.

OFF-THE CAR BALANCING – Procedure in which a tire/wheel assembly is balanced by a bubble or computerized electronic balancer while the assembly is off the vehicle.

ONE-PIECE-WHEEL – Describes a specialty wheel that is cast in one single piece.

ON-/OFF-ROAD – Generally refers to medium/heavy truck tires used on varying surfaces.

OPEN SPLICE – A defect in a retreaded tire caused by failure of the rubber to knit together properly during curing.

ORBITREAD MACHINE – A combined extruder-builder that continuously applies uncured tread rubber to a tire casing in ribbon form.

O RING/L RING – An O- or L-shaped rubber ring used on tubeless OTR tires to seal air between the loose taper seat and the rim base.

OSHA – Occupational Health & Safety Administration

OTR – Off-The-Road, in reference to tires made for heavy mining, quarry, carrying, haulage or construction equipment.

OUNCE INCHES – Expression of the force exerted by a heavy spot (or counterbalance weight) on a tire. Multiply the weight times its distance from the axle center, i.e.. 3 oz. X 7 inches = 21 ounce inches.

OUT-OF-ROUND – Tire or wheel defect in which the tire or wheel is not round.

OUT-RIGGER – Device with retractable mechanical legs used to stabilize equipment such as cranes, ditch diggers, etc., while working.

OUTSIDE DIAMETER – Measurement of a tire when mounted on a wheel and properly inflated.

OVERALL DIAMETER – Maximum height of a tire when mounted on a wheel and inflated to rated pressure.

OVERALL DIAMETER – A retreading measurement used to size a buffed tire casing, usually made on an inflated casing using calipers or a diameter-type rule.

OVERALL WIDTH – Measured from the outer edge of the front of the rim to the outer edge of the back of the rim.

OVERCURE – Vulcanizing uncured rubber for a longer period than necessary or desired. This condition can result in deterioration of the rubber’s physical properties.

OVERDRIVE – Gearing in which less than one revolution of a transmission’s input shaft causes one turn of the output shaft. The purpose of overdrive is to reduce engine rpm in high gear for better fuel economy. Example: A transmission with an overdrive top gear has a ratio of 0.70 to one. Turning the input shaft 0.7 revolutions causes 1.0 revolution of the output shaft.

OVERFLOW/FLASH – Excess tread rubber at the mold parting line or at the edge of the matrix skirt which should be trimmed or buffed off a finished new or retreaded tire.

OVERINFLATION – Inflation of a tire above recommended air pressure, with the resulting negative impacts of rough ride, bruise damage, irregular wear, decreased control and handling, and suspension system strain.

OVERLOADING – Carrying more weight on a tire than its listed maximum carrying capacity, or when a tire’s load carrying capacity – as determined by its size, construction and inflation pressure – is exceeded.

OVERSIZE – Installing a tire larger than needed to carry the load. A common practice on passenger vehicles to increase tire size when replacing OE tires.

OVERSTEER – Cornering condition where rear tires operate at a greater slip angle than the front tires; the tendency of a car to turn more sharply than the driver intends while negotiating a turn.

OWNER-OPERATOR – Trucker who owns and operates his own truck(s). Generally defined as someone who owns and operates less than five tractor/trailers.

OXIDATION – Reaction of a material with oxygen, usually resulting in degradation of the material.

OZONE – A faintly blue form of oxygen produced by the discharge of electricity into the air.

OZONE CHECKING – Cracking of rubber brought about by continued exposure to ozone in the air which, if extensive, is destructive to a tire.

OZONE COMPOUND/ANTI-OZONE COMPOUND - Rubber compounded with certain chemicals to retard ozone damage.

P-METRIC SYSTEM – Tire sizing system, adopted by U.S. tire makers in 1977, using the section width in millimeters, aspect ratio, type of tire construction, and rim diameter in inches (e.g.: P225/70R15).

PADDING GUM – In retreading, heat –resistant rubber used under the tread rubber to build the casing’s size for proper mold fit.

PARALLELISM – Axles are determined to be parallel, thus minimizing tire wear, if a measurement between two or more axles is equal at both ends of the axle.

PATCH – Repair unit such as used for a nail hole.

PATCH/REPAIR UNIT – Reinforcing material, made of rubber and fabric and/or steel cord, used to strengthen the area around a filled tire injury.

PATCH/PLUG – A single repair unit that combines a repair plug or stem with a reinforcing patch. Also known as a combination repair unit.

PAYLOAD – Actual weight of cargo being carried, including packaging, etc. (GVN - unladen weight = payload).

P&D – Pickup and delivery, in reference to the type of truck fleet or operation.

PEAKING – Condition, usually in cushion rubber, resulting from local material starvation and excessive flow from adjacent areas.

PENETRATION – Damage to a tire caused by a piercing object not going completely through the casing.

PERFORATION – Damage completely through a tire caused by a piercing object.

PIGTAIL – Cable used to transmit electrical power from the tractor to the trailer. So named because it is coiled like a pig’s tail.

PIGGYBACK – Semi trailer built with reinforcements to withstand transport by a railroad flatcar. Also known as TOFC.

PINTLE HOOK – Coupling device used in double trailer, triple trailer and truck-trailer combinations. It has a curved, fixed towing horn and an upper latch that opens to accept the drawbar eye of a trailer or dolly.

PITCH – Length from a point on one tread block to the same point on the next tread block. Pitch is varied around a tire to minimize noise.

PLASTICIZER – Chemical compound added to natural and synthetic rubber to impart softness, flexibility or resiliency.

PLUG REPAIR – Filling of a nail hole by forcing repair material into the damaged area to fill it.

PLY – Layer of rubber-coated parallel cords, made of fabric, polymer, fiberglass or steel that make up the cord body of a tire.

PLY ADHESION – Strength of the bonding between adjacent plies, usually expressed as the force required to separate them.

PLY SEPARATION – Parting of the rubber compound between adjacent plies.

PLY RATING – Strength index of a tire, which replaced the old system of marking the actual number of carcass plies in a tire on its sidewall, and is an indication of comparable strength. This system is currently being replaced by the term ‘load range’.

PLY TURNUP – Extension of a carcass ply to its end after wrapping around the bead.

PLOWING – Loss of cornering capability of the font of the vehicle. The car tends to go straight.

PLUS 1/PLUS 2 CONCEPT/PLUS SIZING – Concept to improve handling and performance through the mounting of tires with wider section widths and lower section heights to rims of 1, 2 and sometimes even 3 inches greater diameter.

PNEUMATIC TIRE – Tire designed to be filled with air.

POLYESTER – Strong and lightweight synthetic cord material used in casing construction.

POLYMER – Chemical compound made up of a large number of identical components linked together like a chain.

POROSITY – Minute air pockets in rubber caused by poor mold fit, insufficient rubber or lack of curing pressure.

POSITIVE CAMBER – Condition where the top of a tire is leaning outward from the tire’s vertical centerline, as viewed from the top.

POSITIVE CASTER – Setting where the steering axis is inclined rearward at the top, as viewed from the side; makes possible the self-centering force that tends to return the wheel to the direction the vehicle is traveling.

POSITIVE OFFSET – When the back of the bolt pad is closer to the street side of the wheel; when the mounting face is outboard of the rim centerline, draws assembly towards the vehicle resulting in narrower tracking.

POST INFLATION/PRESSURE TEMPERING – Process of inflating a retreaded tire immediately after removal from a mold or autoclave and keeping it inflated until it has cooled.

POTENTIOMETER – In a retreading shop, a voltmeter that reads low voltage developed at the thermocouple junction as a means to establish temperature.

POWER TRAIN – Components used in transmission of power from the engine to the wheels.

PRECURE – Retreading process of bonding a previously cured tread to a prepared casing using a thin layer of cushion gum (natural rubber), at curing temperatures ranging from 210˚F to 320˚F.

PRECURED TREAD – Retreading tread rubber that has been vulcanized (cured) with the tread element configuration molded into it.

PRE-DRYING – Removing moisture from a tire casing prior to retreading by drying the casing in a heated room.

PRESSURE BUILDUP – Heat causes air to expand, resulting in a normal increase in air pressure. Any increase exceeding 15% above starting cold pressure should be investigated.

PRESSURE PLATE – Retreading term referring to ring-shaped plates in tire molds that can be adjusted to change the cross section of retreaded tires.

PRESSURE TREAD – Proprietary system for applying extruded, patterned, uncured tread stock onto a buffed tire casing, without the use of molds, in a single operation.

PRIVATE CARRIER – Business which operates trucks primarily for the purpose of transporting its own products and raw materials. The principal business activity of a private carrier is not transportation.

PROBE – Pointed tool, like an ice pick or awl, used to determine the extent of injuries during the tire inspection.

PROCESSING – Various stages in the production of new or retreaded tires.

PRODUCTION RETREAD SHOP – Shop that schedules its production not on the basis of day-to-day orders but rather on long runs of purchased casings in order to secure the lowest cost per unit.

PROTECTOR PLY – In a four-belt structure, the top steel belt is designed to protect the three structural belts from injury.

PSI/POUNDS PER SQUARE INCH – Standard measurement of air pressure where 1 psi equals 6.895 kPa or 1 kPa equals .1450 psi.

PTO/POWER TAKEOFF – Device used to transmit engine power to auxiliary equipment. A PTO often drives a hydraulic pump, which can power a dump body, concrete mixer or refuse packer. Some designs mount to a standard opening on the transmission, while others attach at the front or rear of the engine.

PULL – Tendency of a vehicle to veer to one side.

PULL TRAILER – Short, full trailer, supported by axles front and rear, with an extended tongue.

PUNCTURE REPAIR – An off-the-wheel repair to any tire injury caused by a puncturing object. The type or repair used on punctures is determined by the size of the injury.

PUP TRAILER – Short semi trailer, usually between 26 and 32 feet long, with a single axle.

PYRAMID BELT – Belt design in which the upper layer is narrower than the lower layer.

PYROMETER – An instrument to measure the temperature of a tire. In a retreading operation, a pyrometer is commonly used to measure mold surface temperatures or tread rubber temperatures (when used with a penetrating needle).

RACK-AND-PINION STEERING – Steering system now most used for front-wheel drive cars in which a gear at the end of the steering column meshes with a rack of steel teeth; the rack is then connected to the steering arms.

RADIAL CRACKING – Cracking of sidewall rubber running perpendicular to the tire beads. May result from underinflation or exposure to ozone.

RADIAL PLAY – Side-to-side movement of a ball joint.

RADIAL PLY – Refers to the ply or plies used in tire in which the cords run at right angles to the bead and parallel to the tire radius.

RADIAL RUNOUT – Tire assembly that does not form a true circle; the radii of the circle are not equal. Most usual causes are bent wheel (out-of-round) or tire not mounted properly (beads not seated).

RADIAL TIRE – Tire built with casing plies that cross the crown at an angle of 90˚.

RADIUS – Measurement in inches from the wheel axle centerline to the ground when the tire is properly inflated for the load. Also known as loaded radius or static loaded radius.

RADIUS RODS – Metal arms attached to frame and axles for alignment

RAM EXTRUDER – A hydraulically powered batch-loading machine for producing various extruded shapes of uncured rubber for the production of either new or retreaded tires.

RASP – A tool – either a hand tool or an attachment used with a powered drill or buffer – with raised points that is used to texturize and/or shape rubber surfaces.

RATE OF CURE/OPTIMUM CURE – Time required at a specific temperature for a rubber compound to reach its optimum physical characteristics.

RAYON – Synthetic cord material used in casing and belt construction; provides high dynamic strength and good rubber adhesion.

REAM – To clean an injury or hole in a tire prior to repairing.

REAR SPACING/BACKSPACING – Distance from the center mating surface of a wheel to the outer rear edge of the wheel.

RECAP – An incorrect, antiquated term referring to a retread.

RECAPPING – An old term now considered improper, for retreading.

RECIRCULATING BALL SYSTEM – Conventional type of steering system in which steering motion is transferred through a gearbox.

REEFER – Refrigerated trailer with insulated walls and a self-powered refrigeration unit, commonly used for transporting food.

REGROOVING – Act of cutting new tread grooves into the crown of the tire after the original tread is worn down. A practice forbidden by many state laws.

REINFORCEMENT – Any material, usually rubber and fabric, vulcanized to the tire to return strength to the cord body at an injury.

REINFORCEMENT REPAIR – A repair made to a tire casing when an injury extends through more than 25% – but less than 75% – of the tire body. Such a repair requires both a material to fill the injury and a reinforcement patch.

RELUGGING – A method of retreading large OTR equipment tires where the extruded lugs are manually applied to the buffed casing and then are vulcanized to the casing using an autoclave.

REMOLDING – A bead-to-bead retreading process by which both the tread and sidewalls are replaced, giving a new tire appearance.

REPACKING – Repacking of wheel bearings with quality, heavy-duty grease according to manufacturer’s specifications.

REPAIR GUM – Generally applies to warmed uncured rubber stock used to fill a tire injury in a section repair. Can also refer to cushion gum.

RETARDER/BRAKE RETARDER/ENGINE RETARDER/JAKE BRAKE – Device used to assist brakes in slowing a truck or tractor/trailer combination. The most common type of retarder on over-the-road trucks manipulates the engine valves to create engine drag. Other types of retarders include exhaust retarders, transmission-mounted hydraulic retarders and axle-mounted electromagnetic retarders.

RETREAD – A means of extending the life of a tire that has worn its original tread, yet still has a sound carcass. The casing is prepared by buffing off tread rubber and vulcanizing new tread rubber stock in its place. A casing to which tread rubber has been affixed to extend the useable life of the tire after the original tread has been worn out.

RETURNABILITY – Ability of a vehicle to return to a straight-ahead attitude after removal of steering input.

REVERSION – Excessive heating of a cured rubber compound leading to deterioration of its physical properties.

RIBS – Rubber elements at the tire tread which contact the ground, oriented in a generally circumferential direction.

RIDE HEIGHT – Distance between the frame of the vehicle and the road.

RIM – Metal support for a tubeless tire or a tire and tube assembly upon which the tire beads are seated. Also called wheel.

RIM (Truck) – A metal assembly consisting of a base and either a side ring or a side and lock ring combination, which are removable from one side for tire mounting. The opposite side has a fixed flange to retain the tire. Note: Passenger and tubeless rims do not have removable side and lock rings.

FLAT BASE – No taper at either bead seat (obsolete).

INTERMEDIATE – One tapered bead seat of 5° at the fixed flange.

ADVANCED – Both bead seats tapered 5°.

SEMI-DROP CENTER – Both bead seats tapered 5°.

DROP CENTER – Passenger rim has both bead seats tapered 5°, tubeless truck rims have bead seats tapered 15°.

RIM DIAMETER – Diameter of the bead seat on a wheel, not the diameter of the rim edge.

RIM DROP – Area of the wheel’s rim having the smallest diameter, or the space between the rim edge and the beat seat.

RIM FLANGE – Outermost edge of a wheel’s rim to which clip-on weights are attached.

RIM OFFSET – A measurement in inches from the center of the rim (between the flanges) to the tip of the 28° gutter bevel.

RIM PULL – Actual amount of effort, in pounds, available at point of contact of tire and road surface.

RIM WIDTH – Distance between the front bead seat and the rear bead seat.

RMA – Rubber Manufacturers Association.

ROAD HAZARD – Injury to a tire sustained in normal operation, excluding collision or vandalism and that is not reparable by accepted standards.

ROAD WHEEL – Large diameter (typically 67 inches) steer wheel capable of rotating at selected speeds; used to simulate road surface for tire testing.

ROLL-OFF – Bead unseating due to running a tire while flat. Also, the sudden loss of air due to side forces, such as hard cornering, combined with underinflation.

ROLLSTEER – Steering effect induced by load transference from side to side. The axles may move out of their normal parallel) relationship due to spring deflection.

ROLLING RADIUS – Tire dimension from center of the axle to the ground; measured with tire loaded to rated capacity. Used in calculating geared speed.

ROLLING RESISTANCE – Force required to keep a tire moving at a uniform speed. The lower the rolling resistance, the less energy needed to keep a tire moving.

ROTATION – Changing of tire/wheel assemblies from front to rear or from side-to-side on a vehicle according to a set pattern. Common method to help provide even treadwear.

RPM/REVOLUTIONS PER MILE – Number of revolutions a tire makes in a mile at a given load, inflation, and speed.

RUBBER-TO-VOID-RATIO – Ratio between the rubber area and the groove area in a tire footprint.

RUBBING – Condition where a tire rubs against the wheel well or the exhaust system.

RUN FLAT – Damage sustained by a tire due to driving with insufficient air pressure or while flat.

RUN-FLAT – Type of tire designed to maintain driver control when totally deflated, allowing the driver to proceed to the nearest repair facility.

RUNOUT GAUGE – Device used to check and correct radial and lateral runout.

SAE – Society of Automotive Engineers.

SAFETY BEAD – Raised area circling the rim of the wheel and located slightly inward from the bead sear; required on all specialty wheels driven in street use to keep the tire from slipping into the rim bell, if accidentally deflated.

SAFETY LEDGE – Raised area (hump) around the circumference of the bead seat area of passenger wheels Its function is to prevent the tire beads from becoming unseated during hard cornering or while running with low air pressure. A must with tubeless passenger tires.

SCRAP PILE – Discarded tire casings having service life exhausted through wear or damage.

SDC – Semi-drop center rim.

SECONDARY FAILURE – Failure which occurs as a result of a primary failure.

SECTION HEIGHT – Distance from the bottom of the bead to the top of the tread.

SECTION REPAIR – Repair and reinforcement made to the casing when an injury has extended through the tread or sidewall of a tire. The damaged cord is removed and a new cord is replaced in the form of a repair unit or patch. A major repair in the sidewall or tread of a tire. This repair unit must have cord material for reinforcement, made specifically for the type tire-bias-ply or radial.

SECTION WIDTH – Distance from sidewall to sidewall, exclusive of any raised lettering.

SELF-ALIGNING TORQUE – Force which causes a tire/wheel assembly to return to its straight-ahead position after a turn.

SELF-CLEANING TREAD – Tread pattern with tapered grooves and ribs, bars, etc., arranged in a manner that resists packing loose materials, (mud, etc.) in the grooves.

SELF-VULCANIZATION – Vulcanization at room temperature or above, activated by chemical agents without the application of heat from an outside source.

SEMI TRAILER – Truck trailer supported at the rear by its own wheels and at the front by a fifth wheel mounted to a tractor or dolly.

SEMI-TRAILING ARM – Rear suspension system that sues a large A-arm for each wheel; its pivot axis is set between the 0˚ angle of a swing axle and the 90˚ of a trailing arm to a line running straight across the car.

SEPARATION – Parting or debonding of any adjacent parts of the tire (ply to ply, ply to rubber, etc.), usually due to excessive heat.

SERIAL NUMBER – Individual, consecutive numbering of tires during production. It may be a combination of letters and numbers molded on the sidewall.

SERIES – This is the part of the size designation for tires that gives the ratio of the height of a tire (from the rim to the top of the tread) to the width of the tire (from sidewall to sidewall). It is also referred to as the aspect ratio of a tire.

SERVICE DESCRIPTION (LOAD INDEX/SPEED SYMBOL) – Speed rating system which describes the load capacity and high speed of a tire; includes numerical load indexes and alphabetical speed symbols.

SETBACK AXLE – Front steering axle moved rearward from the generally accepted standard position to provide shorter turning radius and more of a vehicle’s weight shifted to front axle.

SET-UP – Premature vulcanization of a rubber compound during processing or storage.

SHELF LIFE – A time limitation for the storage of uncured retread materials (usually 6 months), beyond which certain properties are lost. Storage of materials in a cool, dark, dry environment insures quality.

SHIM – Thin metal plates used as spacers in vehicle alignment.

SHIMMY – Rapid oscillation or wobble of a wheel and tire assembly about the steering axis.

SHIPPING WEIGHT – Dry weight of a truck including all standard equipment, but excluding fuel and coolant.

SHOCK ABSORBER/SHOCKS – A "damper" between the body or frame of the car and the suspension; used to cushion road bumps and bounces and keep the tire in contact with the road.

SHOULDER – The outside edge of the tread face as it wraps slightly over the outer and inner sidewalls, and designed to provide continuous contact with the road while maneuvering.

SHOULDER BLOCKS – Raised rubber-compound segments on the part of the tire tread nearest the sidewall.

SHOULDER GAUGE – Total thickness of a tire in the shoulder area. This is invariably the thickest part of the tire and this gauge directly affects the running temperature of a tire.

SHREDDED WIRE – Short pieces of fine steel wire mixed into a tread or undertread compound.

SIDE RING – Demountable metal flange to hold the tire on the rim base. It can be self contained, locking into the gutter, or may be held in place by a lock ring, depending on the type.

SIDEWALL – Side of a tire between the tread shoulder and the rim bead.

SINGLE BEAD – Refers to a tire built with only one wire bundle in the bead.

SINGLE-PIECE REPAIR – A combination repair unit that features both a stem or plug element and a reinforcement patch element, used to repair puncture injuries.

SINGLES – Tire and wheel assembly, mounted, alone, on one side of an axle.

SIPES – Small, narrow slots molded into the ribs of the tread design which increase the traction edges of the tire and increase the traction ability of the tire on wet pavement. Sipes are especially helpful on wet, icy, or snow covered surfaces

SIZE – Combination of tire width, construction type, aspect ratio and rim size used in differentiating tires.

SKID – To slip, or lose traction, sliding out from the intended direction.

SKID DEPTH – Commonly refers to the depth of a tread.

SKID RESISTANCE – Maintenance of grip on the road and resistance to slide or slip, either longitudinally or laterally.

SKINS – Slang reference to vehicle tires

SKIVE – To cut into. Cut away rubber from an injury in preparation for a section repair.

SLEEPER – Sleeping compartment mounted behind a truck cab, sometimes attached to the cab or even designed to be an integral part of it.

SLEWED AXLES – Axles out of parallel.

SLIDING FIFTH WHEEL – Fifth wheel mounted to a mechanism that allows it to be moved back and forth for the purpose of adjusting the distribution of weight on the tractor's axles. Also provides the capability to vary vehicle combination lengths.

SLIDING TANDEM/SLIDER – Mechanism that allows a tandem axle suspension to be moved back and forth at the rear of a semi trailer, for the purpose of adjusting the distribution of weight between the axles and fifth wheel.

SLIP – Change in distance traveled per tire revolution due to driving or braking conditions; expressed as a percentage of the distance traveled under a free rolling condition.

SLIP ANGLE – Difference between the direction a tire is traveling and the direction it is pointing.

SLOTS – Grooves generally positioned in the ribs and shoulder areas of some tires that aid in wet pavement traction.

SNOW TIRE – A heavily lugged passenger tire primarily designed to deliver enhanced traction in snow. While it is now commonly called a winter tire, snow tires and winter tires are technically different, as winter tires are designed to improve traction on ice, slush and wet pavement in addition to snow. Now identified by M+S icon on the sidewall.

SOAPSTONE – Lubricant used to prevent sticking between tire and tube.

SOLIDS – Industrial tires made without an air chamber.

SPACER – For demountable rims, used in cast spoke mountings, it is a band having the circumference of the spoke wheel and the rims. It fits between two rims in dual mounting to provide clearance between duals.

SPEEDABILITY – Top speed a vehicle can attain as determined by engine power, engine governed speed, gross weight, driveline efficiency, air resistance, grade and load.

SPEED RATING – An alphabetical code assigned to a tire indicating the range of speeds at which the tire can carry a load under specified service conditions.

SPINDLE/KNUCKLE – Device connected to a vehicle's control arm by a ball joint; it is moved by the steering arm to change the direction of the wheels and to transmit braking torque.

SPLIT RIM – Term used to describe an 2 or 3 piece rim that employs a demountable flange.

SPREAD AXLE/SPREAD TANDEM – Tandem axle assembly spaced further apart than the standard spacing of 54 inches. The federal bridge formula favors trailer axles with an eight or nine foot spread by allowing higher weight than on tandems with standard spacing. Trailer axle, usually 6 to 9 feet ahead of another axle and located near the center of the trailer.

SPREADER – Any device, manual or hydraulic, used to spread tire beads for inspection, repair, service, etc.

SPRING – Flexible or elastic member supporting spring weight of vehicle with recovering properties of resuming to original shape when released after being distorted.

SPRING BRAKE – Emergency or auxiliary brake system utilizing a spring load as a force for braking. May be automatically actuated by low air pressure or mechanically controlled for use as a parking brake.

SPRING CLIP – Small metal brackets insuring proper alignment of spring leaves.

SPRING RATE – Rate of deflection versus amount of load applied in other words, how much force is needed to bend a spring a given distance.

SPRING SEAT – Support on which spring is anchored.

SPRUNG WEIGHT – Total weight of a vehicle that is supported by the suspension system.

SPECIFIC GRAVITY – Weight of given volume of substance compared to that of an equal volume of water.

SPEEDOMETER – Instrument to indicate velocity in miles per hour.

SPECIAL MILEAGE TIRE – Regrooveable tire manufactured with an extra layer of rubber between the cord body and the original tread design. This extra layer is designed for the purpose of regrooving, and is specifically labeled as a special mileage commercial tire.

SQUIRM – Footprint distortion of a rolling tire; usually hourglass in shape on a straight road and crescent-shaped on curves.

STABILITY – Ability of tires to maintain direction of a vehicle on curves without causing excessive body sway.

STABILIZER – Device used to stabilize vehicle during turns sometimes referred to as a sway bar.

STABILIZING PLIES – Two or more plies, of steel, fiberglass, etc., forming a belt around the circumference of a tire, between carcass and tread rubber. It reduces tread distortion of radial and bias belted tires.

STACKED BELT – Belt design in which both layers are of equal width.

STANDARD LOAD – P-Metric tire with a maximum inflation pressure of 35 psi.

STANDARD RIM – A wheel that has been calibrated and found to meet the precise measurements specified by Tire and Rim Association, or, where applicable, by European Tire & Rim Association.

STAR PATTERN – Proper method for sequential torquing of lug nuts in a 5-lug bolt circle.

STATIC – Having no motion.

STATIC BALANCE – Balance at rest. A condition in which a tire and wheel assembly has equal weight around the wheel’s axis of rotation.

STATIC LOADED RADIUS – Measurement from the middle of the axle to the road surface; measured with the tire inflated to required pressure and carrying the rated load.

STEEL BELT – Belt material used in tires with high stiffness that provides good handling and low tread wear.

STEEL BELTED RADIAL – Radial construction tire that features one or more steel belts to add stability and protection.

STEER AXLE – Front axle on a truck by which the vehicle is steered.

STEER WHEELS – Wheel(s) that direct the course of a vehicle.

STEERING ARMS – Another name for tie rod arms, arms attached to front axle steering system to effect turn of wheels.

STEERING AXIS – Imaginary line drawn through the center of the steering pivots. The axis about which the wheel pivots when turned.

STEERING AXIS INCLINATION – Truck angle where the inward tilt (side to side) of the kingpin or spindle support arm, at the top, from the vertical. Thus a line drawn down through the center plane of the tire and a line through the kingpin, or ball joints, would come closer together at the ground than at the top.

STEERING KNUCKLE – Steel forging which includes the wheel spindle. In cars it is the spindle support arm which pivots on ball joints. In trucks with non-independent front suspension, it pivots on the kingpin.

STEERING RESPONSE – Reaction time between driver input at the steering wheel and the directional change of the vehicle.

STEERING SYSTEM – Major control mechanism that multiplies driver input on the steering wheel into the motion of turning a vehicle's front wheels.

STITCHING – Hard-rolling method used to both remove trapped air and improve rubber contact for better adhesion, during repair and retreading.

STRAIGHT TRUCK – A non-articulated hauling vehicle.

STRING REPAIR – An uncured strip of rubber that is used to temporarily fill a tire puncture.

STRIP STOCK/STRIPPING STOCK – A rubber stock used to extend the wing of tread rubber.

STUD HOLES – Small cavities along a tire's tread designed to hold tire studs for increased traction on snow-covered surfaces.

SULFUR – Chemical element used in the vulcanization process.

SUSPENSION – System of devices supporting the upper part (body and chassis) of a vehicle on its axles.

SUSPENSION PACKAGE – Specialized kit of suspension components designed specifically for individual makes and models of vehicles; usually sold to improve performance.

SUV – Sport utility vehicle.

SWING AXLE – Rear suspension system comprised on half shafts with universal joints only at their inward ends on either side of the differential.

SWING OUT – Tendency of the rear tires of a vehicle to break away during sudden steering maneuvers.

SYMMETRICAL TREAD PATTERN – Unlike asymmetrical patterns, symmetrical tread patterns have a consistent look across the tire’s face, with both halves of the tread face having the same design.

SYNTHETIC RUBBER – Rubber made from chemicals as a substitute for natural rubber; properties can be tailored for specific needs.

TANA – Tire Association of North America.

T&RA – Tire and Rim Association

TACHOMETER – Instrument to indicate engine speed in revolutions per minute.

TACK – Term used to describe the sticky quality of a rubber compound.

TALC – Powder lubricant to prevent sticking between tube and tire.

TANDEM AXLES – Combination of two axles having a common suspension.

TANDEM DRIVE – Two powered axles in combination.