745
Maintenance
4. Tire ply composition and mate-rial
The number of layers or plies of rub-
ber-coated fabric in the tire. Tire
manufacturers also must indicate the
materials in the tire, which include
steel, nylon, polyester, and others.
The letter "R" means radial ply con-
struction; the letter "D" means diago-
nal or bias ply construction; and the
letter "B" means belted-bias ply con-
struction.
5. Maximum permissible inflationpressure
This number is the greatest amount
of air pressure that should be put in
the tire. Do not exceed the maximum
permissible inflation pressure. Refer
to the Tire and Loading Information
label for recommended inflation
pressure.
6. Maximum load rating
This number indicates the maximum
load in kilograms and pounds that
can be carried by the tire. When
replacing the tires on the vehicle,
always use a tire that has the same
load rating as the factory installed
tire.
7. Uniform tire quality grading
Quality grades can be found where
applicable on the tire sidewall
between tread shoulder and maxi-
mum section width.
For example:
TREADWEAR 200
TRACTION AA
TEMPERATURE A
Tires degrade over time, even when
they are not being used. Regardless
of the remaining tread, we recom-
mend that tires be replaced after
approximately six (6) years of normal
service. Heat caused by hot climates
or frequent high loading conditions
can accelerate the aging process. Tread wear
The tread wear grade is a compara-
tive rating based on the wear rate of
the tire when tested under controlled
conditions on a specified govern-
ment test course. For example, a tire
graded 150 would wear one-and-a-
half times (1½) as well on the gov-
ernment course as a tire graded 100.
The relative performance of tires
depends upon the actual conditions
of their use, however, and may
depart significantly from the norm
due to variations in driving habits,
service practices and differences in
road characteristics and climate.
These grades are molded on the
side-walls of passenger vehicle tires.
The tires available as standard or
optional equipment on your vehicle
may vary with respect to grade.
Maintenance
46
7
Traction - AA, A, B & C
The traction grades, from highest to
lowest, are AA, A, B and C. Those
grades represent the tire’s ability to
stop on wet pavement as measured
under controlled conditions on spec-
ified government test surfaces of
asphalt and concrete. A tire marked
C may have poor traction perform-
ance.
The traction grade assigned to this
tire is based on straight-ahead brak-
ing traction tests, and does not
include acceleration, cornering,
hydroplaning, or peak traction char-
acteristics. Temperature -A, B & C
The temperature grades are A (the
highest), B and C representing the
tire’s resistance to the generation of
heat and its ability to dissipate heat
when tested under controlled condi-
tions on a specified indoor laboratory
test wheel.
Sustained high temperature can
cause the material of the tire to
degenerate and reduce tire life, and
excessive temperature can lead to
sudden tire failure. Grades B and A
represent higher levels of perform-
ance on the laboratory test wheel
than the minimum required by law.
Tire terminology and definitions
Air Pressure:
The amount of air
inside the tire pressing outward on
the tire. Air pressure is expressed in
pounds per square inch (psi) or kilo-
pascal (kPa).
Accessory Weight: This means the
combined weight of optional acces-
sories. Some examples of optional
accessories are, automatic transmis-
sion, power seats, and air condition-
ing.
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.
