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Adjustment - An allowance given to the customer to be used

toward the replacement of a tire because of warranty or

service issues.

Alignment - The checking and adjustment of camber, caster

and toe angles of the vehicle’s suspension to maintain proper

steering and handling of the vehicle for maximum performance.

Air Pressure - Force exerted by air within a tire, expressed in

pounds per inch in USA and Bar in Europe.

Aspect Ratio -A numerical term which expresses the relationship

between the standing height of the tire and the cross

section width. (Aspect Ratio of 70 means the tire section

stands approximately 70 percent as high as it is wide between

the sidewall.)

Balance -The equal distribution of the mass of the tire and

wheel assembly for smooth driving. Balance is achieved

by fitting weights to the wheel rim to off-set uneven weight

distribution of the tire, wheel or brake assembly.

Bead -The part of the tire that is shaped to fit the rim at the

rim flange and the bead seat. Made of high tensile steel wires

that are wrapped in woven fabric and then held by the plies

and molded rubber. On clincher tires or (beaded edge tires)

the bead is a hard rubber core reinforced by cord material in a

specialized shape.

Bias Tires - Pneumatic tires having crossed layers of ply cord

(usually two, four or more) running diagonally from bead

to tread.

Bias Belted Tires - These tires have a body similar to that

of bias tires, with the addition of two or more belts under the

tread to strengthen and stabilize the tread. The belts improve

tread life by reducing tread movement during contact with

the road.

Bolt Pattern -The pattern of holes on a rim or wheel which the

bolts that mount the wheel to the vehicle are affixed.

(See page 63)

Camber - The measurement of tilt of the tire and wheel

assembly on the front end of the vehicle off vertical

measured in degrees.

Carbon Black - Substance used in tire manufacturing as a

reinforcing material in the rubber mixing process which gives

the rubber a higher resistance to premature wear.

Clincher tires - Early type of tire construction (as used on Ford

Model T pre-1926). Clincher beads have a hard rubber core reinforced

by cord material in a specialized shape with no steel in

the bead. Air pressure is very critical to proper fitment of these

tires. These tires are also referred to as Beaded Edge tires.

Contact Patch - The area of the tire that comes in contact

with the road.

Cord - The twisted fiber or filament of polyester, rayon, nylon

or steel which gives the tire body and belts strength.

Cross Section - The linear distance between the exterior

sidewalls of an inflated tire at the maximum width.

Crown - The center area of a tire’s tread footprint.

Detachable rim - Early style automobile rim permanently

fixed to the wooden wheel. This type of rim has one or two

side rings and possibly a separate lock ring to secure the tire

assembly on the rim (see diagram on page 49 under

Stanweld rim).

Demountable/Detachable rim - Same as above except this

rim removes from the wood wheel and is secured to the wood

wheel by a series of lugs and lug bolts and clamp rings. (See

diagram on page 49 under Stanweld rim)

DOT Number - Number molded onto the tire indicating the

Manufacturer and date of Manufacture as registered with

the United States Department of Transportation. A tire with a

branded number near the DOT number classifies the tire as a

retread. Responsibility passes to the Retreader.

Footprint - The area of the tire tread that is actual contact with

the ground or road surface.

Drop center - The drop portion of a rim cross section between

the bead seats or rim flanges in which a bead is placed during

the mounting process.

ECE Number - ECE (Economic Commission of Europe)

developed testing standards for vehicles and tires which apply

to dimensions, loads, tire markings and speed ratings.

ETRTO - European Tire and Rim Technical Organization.

Green Tire - A tire that has not yet gone through the process

of vulcanization or curing in the tire molding process.

Gross Vehicle Weight - Total weight of a vehicle including all

fluids, cargo and passengers.

Inner Liner - The layer of rubber which is laminated to the

inside of a tubeless tire to insure the air retention quality of the

tire body.

Hub centric - Wheels manufactured to match and true the

diameter of the bead seats off of the center hole of rim.

High Pressure tire - 100 percent aspect ratio tire with cross

section equaling section height. This type tire was used on example

would be 35x5. The height of the tire should be 35

inches, the cross section should be 5 inches on a 25 inch rim.

Kilopascal - Metric unit for air pressure specifically in European

use tires. One psi equals 6.9 kPa.

Lateral runout - Side to side movement of a

wheel assembly.

Load Carrying Capacity - Maximum load for which the tire is

designed under standard conditions.

Load Index - Relative load carrying capacity as originated by

European community, refers to the maximum load carrying

capacity in kilograms and/or pounds.

Load Range - A system of designations, which identifies the

carrying capacity range of a tire. These markings shown on the

tire indicate the ply rating established for the tire such as B (4-Ply

rating), C (6-Ply Rating) and D (8-Ply rating). This system was

established by the Rubber Manufacturers Association.

Lug centric - Wheels manufactured to match and true the bead

seat diameters off the lug holes.

Matched slicks – Rear drag tires that when inflated to recommend

PSI, have matching circumferences.

Matching balance system - A computer balancing system used

to match the high point of a rim to the low point of a tire diameter,

creating a more perfecting round total assembly.

Maximum Inflation Pressure - The maximum air pressure in kpa/

bar or psi that a tire can be inflated while cold. Usually found on

sidewall of tire.

M+S - The designation of a tire that meets the requirements given

by RMA to be used for all seasons.

NHTSA - National Highway Traffic Safety Administration


Overall diameter - The diameter of an unloaded inflated tire,

measured from the crown on one side to the crown on the opposite

side. The free radius equals one-half the overall diameter.

Overinflation - The condition that exists when a tire is inflated

beyond the pressure corresponding to the actual load or beyond the

vehicle manufacturer’s recommendation.

P-Metric - A tire sizing system where the section width is shown

in millimeters, the aspect ratio, type of construction and finally rim

diameter are shown in inches example; (P205/75R15).

Plus One - From original equipment size tire and wheel, choosing

to go up in rim diameter one inch while keeping the same overall

diameter. Usually always adds width to rim and tire and decreases

sidewall section height. Key is to keep same exact diameter to

keep rolling circumference same.

Ply - A layer of rubber-coated parallel cords forming the tire body

or carcass.

Polyester Cord - A synthetic fiber that excels in maintaining

strength properties at high heat levels, and eliminates flat spotting.

Post Inflation - When tires are removed from the mold after the

curing process, they are mounted on a rim and inflated to their

proper inflation, during the cooling period, to allow the tire to cool

keeping its correct shape and size.

PSI - A measure of air pressure commonly used throughout the

world signifying pounds per square inch.

RMA - Rubber Manufacturers Association. (www.rma.org).

Radial Ply - A tire with cords running radially from bead to bead

(90 degrees to centerline of the tire). Radials have the addition of

one or more belts under the tread to strengthen and stabilize

the tread.

Radial runout - Up and down movement of a

wheel assembly.

Rayon - A fiber used in tire construction made from cotton or

wood pulp by chemical process.

Ribs - Part of the tire tread design created by grooves running

circumferentially around the tire.

Revolutions Per Mile - (R.P.M.) - The number of revolutions that

the mounted tires will make in one mile, at rated load and inflation.

Rolling Resistance - The resistance of a tire to free rolling.

Roll out - Term used for drag tire circumference, and is the number

of inches the tire rolls before it has traveled back to its initial

starting point.

Section Height - The height of a tire measured from the rim to the

outside measurement of the tread.

Section Width - Measurement of distance through cross sectional

width of a tire at widest part, exclusive of scuffing rib when inflated

to normal pressure and not under load.

Shoulder - The edge of a tire’s tread where the tread joins

the sidewall.

Single Tube Tire - This is one of the earliest types of tire constructions

as used on early automobiles, motorcycles and bicycles,

where the tire and tube are made together and are fitted onto a rim

with a semi-circle cross-section. The cord angles of the construction

allow for the tire to tighten on the rim as it is inflated. These

tires often have lugs for securing to the rim. They are often glued

on the rims as well.

Sipe - To cut across a tire tread to produce biting traction edges.

Also refers to the thin slots in the tread of a tire designed to aid in

wet traction and water removal.

Speed Rating - A speed designation of S, T, H, V or Z shown

in the size marking of some tires. (See pg. 47)

Synthetic Rubber - Rubber made by man using chemicals as

opposed to natural rubber harvested from trees. Most tires

today are made of this type rubber.

Tire Storage - Tires should be stored horizontally in a clean,