Adjustment - An allowance given to the customer to be used
toward the replacement of a tire because of warranty or
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
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
Bias Tires - Pneumatic tires having crossed layers of ply cord
(usually two, four or more) running diagonally from bead
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
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
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
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
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
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
Radial runout - Up and down movement of a
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
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
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,