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A-2
Term used for tire sizes 16.00 and larger in nominal cross section. Also referred to as earthmover or off-the-road tires (O.T.R.).
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Aging
Deterioration of rubber properties by oxidation over a period of time.
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Air stop
Registered for trademark for Michelin tubes.
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Alignment
Wheel alignment is the mechanics of keeping all interrelated parts which affect steering in proper adjustment. There are five steering angles involved:
(a) Camber
The inward or outward tilt of the wheel at the top from the vertical. Positive tilts outward and negative tilts inward. It is measured in degrees.
(b) Caster
The forward (negative), or rearward (positive) tilt of the kingpin at the top from the vertical, when referring to trucks. In cars having independent front suspension, the upper ball joint is set forward or rearward in relation to the lower ball joint. Caster is measured in degrees. See 'trail distrance'.
(c) Toe-in/Toe-out
The front tires of a vehicle are adjusted closer together in the front than at the back for toe-in. The opposite setting is toe-out. It is measured in fractions of an inch.
(d) Kingpin inclination/steering axis inclination
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. See 'center distance'.
(e) Turning radius (Toe-out on turns)
The front tires assume a toe-out relationship to one another when making a turn. This makes allowance for the fact that they are forming different size circles around a common center. (Sometimes called the Ackerman System).
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Ambient temperature
The surrounding air temperature.
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Angular vibration
Side to side movement or shimmy of a tire. See 'BALANCE, DYNAMIC.'
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Anti-skid system
Computer Brake Control. A system installed on many vehicles to prevent skids caused by wheel lock-up. It allows for automatic adjustments in braking pressure for maximum braking force without loss of steering control.
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Aquaplaning
See 'hydroplaning'.
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Aspect ration
The ratio of 'section height' to 'section width'. Section height divided by section width of a tire expressed as 78 series, 70 series, etc. The section height is 70% of the section width when referring to 70 series. These are low profile tires, and may be called ultra low profile.
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Awl
A pointed or flat tool used to probe nail holes and injuries.
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Axle live
Driven axle.
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Axle, ratio
See 'GEAR RATIO'.
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Balance patch
A factory installed patch used to bring a tire within quality control balance tolerances before distribution. It is placed inside the tire casing and looks much like a nail hole repair patch.
Tire balance
A tire properly weighted so that it rotates without causing bounce or vibration:
Unbalance
A tire that is not weighted properly can cause vibration. The condition is exaggerated by centrifugal force which increases as speed is increased and by the distance the heave spot is from the wheel axis. (See 'ounce inches'.)
Static balance - (kinetic)
A tire that has a heavy spot at any point around its circumference. The heaviest point will come to rest at the bottom when the tire is rotated on a free bearing. On a vehicle, the tire will tramp or bounce.
Dynamic unbalance
Exists only when the wheel is rotating and is caused when a heavy spot in the tire is not in the center plane of the wheel, or when a heavy spot is not in the same plane as the static counter-balance weight. On a vehicle the tire would wobble from side to side.
On-car-balancing
Balancing of tire using a machine capable of balancing tire, wheel and brake assembly while the tire is properly mounted on the vehicle.
Off-car-balancing
The tire assembly is removed from the car and mounted on a balancing machine.
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Balance weight
The most common are lead blocks of varying sizes marked by weight in ounces (or fractions of an ounce) and having metal dips for attaching to the rim flange
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Ball joints
Upper and lower ball joints, attached to upper and lower A-frames and spindle support arm in vehicles having independent front suspension, provide for pivoting of front wheels for steering.
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Ballasting
The addition of weight, liquid or dry, inside the tire to act as a counterbalance, to increase traction, reduce wheel spin and dampen out bounce:
Liquid
Usually water mixed with calcium chloride to prevent freezing and increase specific gravity.
Dry
A fine powder of barium sulphate. Sometimes referred to incorrectly as lead ballast because of one brand name, "Ledballast".
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Bead expander
Any of several devices used in the mounting of tubeless tires to prevent inflation air from escaping and bring the tire beads against the tapered bead seat area (rim). Also see 'spreader tire'.
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Bead movement (bead rocking)
Movement of bead on rim caused by improper inflation, excessive loading, improper design, improper seating or improper rim or tire size.
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Beads
The parts of the tire that seat on the rim. Bead heel, sole and toe form a foot-like shape.
Bead points
A feathered rubber extension of the bead toe used where a flap is not required; protects the tube from chafing between bead toes and rim base.
Bead seat diameter
The measurement of tire diameter, at the bead heel, where it seats on the rim. It is marked on the tire sidewall following 'section width'.
Bead wires
Steel wires wound circumferentially and placed in the beads, and by their tension prevent the beads from lifting over the rim flanges.
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Belted
Refers to a tire having a stabilizing belt, of two or more plies of steel, fiberglass, etc., running circumferentially around the tire between the carcass and the tread rubber. The carcass can be either radial or bias ply.
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Bias belted
A tire consisting of a conventional bias ply carcass with the addition of a belt of rayon, nylon, fiberglass, or steel running circumferentially in the tread area. See 'BELTED'.
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Bias ply-conventional bias-ply
A tire having two or more carcass plies arranged in a criss-cross manner and diagonally to the beads and travels approximately 1/3 the distance around the circumference before attaching to the other bead. Each cord in the next ply is arranged in the same manner, but in the opposite direction.
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Bleeding
The harmful practice of reducing the pressure in tires that have been run, warmed up and thus increased from their starting pressure.
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Blemish - (blem)
A tire having a slight imperfection in appearance that will not affect tire life or safety.
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Blister
A localized bubble on the surface of a tire, normally caused by a separation between plies or between surface rubber and a ply.
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Blowout
Instantaneous rupturing of tire body, causing complete loss of air pressure.
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Boot
A simple protective device (sometimes a piece of tube, tire, etc., cut to size) placed between the casing and tube. It offers temporary protection for the tube against pinching by an injury in the casing. It is not a repair of the injury and is unsafe to use.
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Bottom dumps
Trailers that unload through bottom gates.
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Brake fade
The loss of effectiveness of braking, usually after becoming hot from continual or repeated use in a short period of time.
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Brakes-disc
A braking system, effective in forward or reverse direction, consisting of a revolving steel disc (rotor) and brake pads which make contract with this disc under hydraulic pressure. It is resistant to fading in severe heat and wet conditions.
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Brakes-drum
Single leading brake shoe type
The use of a single hydraulic plunger and a common pivot point expands two shoes against the drum with equal pressure whether braking from forward or reverse direction. Leading brake shoe usually termed 'primary shoe', trailing shoe termed 'secondary shoe'.
Double leading brake shoe type
The use of two hydraulic plungers and separate pivots allows for more effective braking in the forward direction, though not very effective in reverse.
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Brand number
An identification burned into sidewall rubber of a truck tire by some customers. Often it is coded to show company's initials, mounting date, etc.
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Breakaway
The loss of traction as in turning with such force that the tire suddenly loses all contact with the ground. A tire having greater tread stability than a Bias ply (bias-belted or radial) can resist breakaway longer.
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Bridge (LEMNA)
A metal support easily installed in the valve slot of a rim without dismounting the tire. It prevents the flap and tube from bulging through the slot under high pressure and high heat conditions.
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Bridgewasher
A protective thin metal washer sometimes installed at the valve stem between the flap and rim base to prevent tube and flap from protruding through the valve slot due to high pressure and high temperature.
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Bruise
An injury to a tire, weakening, breaking, or separating cords in the carcass without cutting or tearing of surface rubber.
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Burred wheel
Wheel with rough slivers or projections of metal around rim edges.
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Buttress
Heavy rubber reinforcements in the tire shoulder. It provides support at the edge of the tread, limits shoulder area flexing and protects the shoulder of off-road tires.
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Butyl
A non-porous synthetic rubber used to manufacture most tubes and as an air proof liner for tubeless tires.
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Cab
Driver's compartment of a truck.
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Calcium chloride
Chemical added to prevent freezing of water ballast in farm tires and EM tires.
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Calendering
A thin layer of rubber inside the tire casing covering the carcass cords, protecting them from moisture and giving protection to the tube against chafing by the cord-body. In tubeless tires, calendering consists of a layer of air proof rubber (Butyl).
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California wheel
An incorrect term reflecting a brand name for a previous manufacturer of cast spoke wheels. A popular wheel in the East and Midwest but not frequently used in California or other Western states.
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Camber
See 'alignment'.
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Camber axle
An axle beam formed in a slight arc, curving upward at the center to allow the tires to tilt outward at the top. It compensates for normal axle sag under load.
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Capping
See 'retreading'.
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Carbon black
A by-product of the petroleum industry used as a pigment and to give body in the manufacture of rubber products, both natural and synthetic. Carbon is the black residue from burning petroleum.
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Carcass
The cord body (ply/plies). The foundation structure of a tire that provides strength to hold air pressure within the casing.
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Carrying capacity
The maximum load that should be permitted on a given tire, wheel, or rim, etc., as recommended by the manufacturer's data book.
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Casing
The tire without tube, flap, or tim.
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Casing factor
That portion of the load supported by casing stiffness instead of air pressure.
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Caster
See 'alignment'.
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Cement
An adhesive rubber compound dissolved in solvent used to provide building tack and cured adhesion. May be brushed or sprayed on the buffed surface.
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C.G.
Center of gravity. A point within the length, width, and height of a vehicle about which all the vehicle weight is balanced.
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Chain drive
Rear axle driven by means of a chain belt.
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Change-over
Removing new original equipment tires in trade for a different make, size or type.
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Channel
See 'groove'.
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Chassis
The basic truck frame, including suspension, steering, driving and power components, excluding cab or body.
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Chassis, cab
Truck chassis including driver compartment.
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Chassis, cowl
Truck chassis with front fenders and hood complete with instrument panel. For use with custom built body and cab.
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Check valve
A one way valve used to prevent pressure loss.
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Checking
Minute cracking in surface of rubber caused by aging and oxidation.
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Chemical cure
Vulcanization at room temperature or above, activated by chemical agents without the application of heat from an outside source.
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Chipping
Flaking or tearing away small bits of tread rubber.
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Chunking
Tearing or breaking away pieces of tread rubber
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Circumferential break
A tire injury running parallel to the bead.
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Circumferential crack
A crack in a tire running parallel to the beads. Usually consists of cracks in the grooves of the tread
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Clearance
Between dual - See 'dual spacing'.
Vehicle to tire: Minimum -
A. To a fixed part: 5/8' (15mm)
B. To a moveable part: 1' (25mm)
Vertical
The distance between the top of the tread and some part of the vehicle closest above it, after subtracting the axle stop clearance and any increase in tread depth from the existing tire.
Longitudinal
The distance between the tread and the closest point forward or rearward, reduced by increase in tread depth and rearward movement of the axle under load (1/3 the distance between shackle pin centers).
Lateral
he distance between the tire sidewall and the nearest point on the vehicle, reduced by any increase in rim offset and 1/2 any increase in tire section from the existing tire.
Front wheel clearance
The distance between the tire and the closest point on the vehicle laterally, longitudinally and vertically, checked to lock and all intermediate points.
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Coefficient of friction
The horizontal force required to move a body (on a relatively smooth level surface) divided by the weight of the body. The coefficient of rolling friction is the maximum retarding force (that can be applied to a rolling body on a relatively smooth level surface without causing a cessation of rolling) divided by the weight at the contact surface.
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Coil spring
Spring stock coiled in cylindrical form.
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Commercial tires
Generally indicating truck and industrial tires.
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Conventional tire
See 'bias-ply'.
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Containerization
Shipping system based upon large cargo-carrying containers that can be easily interchanged between trucks, trains, and ships without rehandling of contents.
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Contract carrier
An operation transporting under contract with an individual shipper.
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A strand of fabric material or steel cable used in the ply of a tire.
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Cost per mile
The actual cost of a tire after considering all costs (price of tire, price of retreads, repairs, services, etc.) less any credits (warranty, etc.), divided by the total number of miles it has run. True cost per mile can be figured only after the tire is no longer serviceable and should include costs to the user incurred as a result of downtime.
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Cracking tread or groove
Splitting in grooves caused by excessive strain.
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Cross section
See 'section width'.
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Cross member
Structural shape tying in side rails of frame.
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Crown
The tread area of a tire.
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Crown radius
The measurement of the curvature of a tire tread between the shoulders of the tire. Expressed as a percentage, it indicates the relative flatness of the tire tread area.
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Crown width
The distance shoulder to shoulder measured along the buffed contour.
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Cure time
The time required at a reference temperature for a compound to reach optimum physical properties.
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Curing
Process of heating or otherwise treating a rubber or plastic compound to convert it from a thermoplastic or fluid material into the solid, relatively heat-sensitive state desired in the commercial product. When heating is employed, the process is called vulcanization.
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Cushion gum
A soft, tack rubber compound used in retreading and repair to facilitate bonding between different rubber compounds and between plies, etc.
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Dead axle
The non-powered axle of a tandem rear mounting in which the other axle is powered.
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Deflection rate
Generally refers to rate of spring deflection to inches per 1000# load.
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Demountable rim
See 'rim and wheel terms'.
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Differential
An arrangement of gears at the center of a drive axle that allows the wheels on one side to go faster (or slower) than wheels on the other side, as in rounding curves.
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Directional tread
An arrangement of bars, grooves and ribs in any manner that gives most effective traction when the tire revolves in only one direction.
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Disc wheel
The combination of a rim and a metal disc riveted or welded together. The disc is usually offset from the centerline of the rim to allow for dual tire mounting and to provide sufficient clearance between duals. Disc wheels are attached to the hub with either single nuts or double cap nuts.
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Dish
Offset. See 'rim and wheel measurements'.
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DOT.
Department of Transportation, a federal agency.
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DOT number
The symbol DOT means the tire meets or exceeds Department of Transportation safety standards. Following DOT are a maximum of eleven numbers.
Example: DOT FT TW A2NX 092:
DOT-Meets or exceeds standards.
FT-Identifies manufacturing plant
TW-Code for tire size.
A2N or A2NX-3 or 4 digits optional with manufacturer to identify characteristics of the tire.
092-Week of mfg., in this case, 9th week of 1972.
Prior to May 22, 1971 only the manufacturer's plant was identified by three numbers -- (Example DOT 129). Retreaded tires must also have a new serial number and can be determined by the letter "R" following DOT letters. |
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Dowel pin
A pin aligning or securing two parts to prevent movement between them.
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Downtime
The vehicle operating time lost due to maintenance difficulties, tire damages, etc.
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Drag link
Connection between Pitman Arm and Steering Ball (Steering Arm) on front axle of a vehicle.
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Drift
See 'tire deviation angle'.
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Drive train
Components used to propel vehicle.
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Drivers
Drive axle tires (slang usage).
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Drivers, rim
Riveted or welded metal blocks or extrusions on both sides of the valve slot to prevent valve damage due to rim slippage on cast spokes.
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Drop center rims
See 'rim types'.
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Dual axles
See 'tandem axles'.
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Dual bead tires
Heavy service and large truck tires using two or more sets of bead wires in each bead rather than one.
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Dual mountings
Tandem axles, both powered directly by the engine. (Slang term, twin screw.)
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Dual spacing
A measurement in inches from the center of the tread of one tire, to the center tread of the other tire in dual, which provides clearance between duals for air circulation.
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Dump body
Metal body generally hinged at rear and dumped by hydraulic means. Size generally given in cubic yard water level capacity.
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Durometer
A device to indicate the hardness of rubber.
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Dust cover
A soft, flexible valve cap to protect valve assembly from dust while in shipment and storage. It is not capable of sealing the air pressure and should not be used in service.
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Dust shield
Sheet metal disc or plate placed on brake assembly to keep debris from brake assembly.
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Dynameter
Electric or hydraulic instrument used in determining power output of engine, or friction in chassis components.
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Dynamic balance
See 'balance'.
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Elastometer
A term which includes natural rubber and the many synthetic materials that possess rubber-like properties.
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End dump
A term used to describe various dump trucks or trailers that tilt to unload at the rear.
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Engine break
(Energy retarder)
A system that allows for slowing of a vehicle that is independent of the conventional braking systems. A driver would normally down-shift to slow his descent of a hill, using engine compression. The 'engine brake increases the effectiveness of this retarding force.
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Extruder
A machine that shapes a rubber compound into a usable form. Uncured rubber is heated, to soften, and forced through dies having the desired shape and dimensions.
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Fabric fatigue
Fabric degradation and resultant tire cord breakdown due to repeated flexing and heat.
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Flange seal
An "L" shaped rubber seal used in some earthmover tubeless tire mountings. It prevents air loss between the tire beads and the: (1) flange and rim base, and (2) flange and loose taper seat. Also see 'O ring'.
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Flap
A 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.
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Flat spot
Irregular wear in an isolated spot or spots around the tire tread.
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Flipper strip
See 'ply turnup'.
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Flotation
Ability to float generally referring to large low pressure tires. (The ability of a tire, to pass over soft surfaces without sinking in.)
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Foot pound
One pound of force at the end of a one hot last lever; a measurement of torque i.e., 3ft. bar x 150 Ibs.= 450 foot pounds).
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Fork lift (lift truck)
A machine having metal arms extended in front for picking up and moving pallets or skids.
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Frame
The backbone structure around which the vehicle is assembled.
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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.)
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Free rolling wheel
A non-powered wheel position on a vehicle, such as steering axle, tag axle or trailer wheel positions.
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