Vehicle Care 10-51
(B) Tire Width : The three‐digit
number indicates the tire section
width in millimeters from
sidewall to sidewall.
(C) Aspect Ratio
: A two‐digit
number that indicates the tire
height‐to‐width measurements.
For example, if the tire size
aspect ratio is 60, as shown in
item C of the illustration, it would
mean that the tire's sidewall is
60 percent as high as it is wide.
(D) Construct ion Code
: A
letter code is used to indicate
the type of ply construction in
the tire. The letter R means
radial ply construction; the
letter D means diagonal or
bias ply construction; and the
letter B means belted‐bias ply
construction.
(E) Rim Diameter
: Diameter of
the wheel in inches.
(F) Service Description
: These
characters represent the load
index and speed rating of the
tire. The load index represents
the load carrying capacity a tire
is certified to carry. The speed
rating is the maximum speed a
tire is certified to carry a load.
Tire Terminology and
Definitions
Air Pressure : The amount
of air inside the tire pressing
outward on each square
inch of the tire. Air pressure is
expressed in kPa (kilopascal)
or psi (pounds per square inch).
Accessory Weight
: The
combined weight of optional
accessories. Some examples
of optional accessories are,
automatic electric drive unit,
power steering, power brakes,
power windows, power seats,
and air conditioning.
Aspect Ratio
: The relationship
of a tire's height to its width.
Belt
: A rubber coated layer of
cords that is located between
the plies and the tread. Cords
may be made from steel or other
reinforcing materials.
Bead
: The tire bead contains
steel wires wrapped by steel
cords that hold the tire onto
the rim.
Bias Ply Tire
: A pneumatic
tire in which the plies are laid
at alternate angles less than
90 degrees to the centerline
of the tread.
Cold Tire Pressure
: The
amount of air pressure in a tire,
measured in kPa (kilopascal)
or psi (pounds per square inch)
before a tire has built up heat
from driving. See Tire Pressure
on page 10‑54.
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