Uniform Tire Quality Grading Stand-
ards Overview of Tire Quality Grading
Standards
Uniform Tire Quality Grading Standards are
U.S. government specifications. Their pur-
pose is to provide drivers with uniform relia-
ble information on tire performance data. tire manufacturers have to grade tires using three
performance factors: tread wear 0043, tire trac-
tion 0044and heat resistance 0087. All tires sold
in North America are provided with the cor-
responding quality class mark on the sidewall of the tire, even though these regulations do
not apply to Canada.
i The actual values for tires are vehicle-
specific and may deviate from the values in
the illustration.
Where applicable, the tire grading informa-
tion can be found on the tire sidewall between
the tread shoulder and maximum tire width.
For example: Treadwear Traction Temperature
200 AA A
All passenger car tires must conform to the
statutory safety requirements in addition to
these grades. Treadwear
The treadwear grade is a comparative rating
based on the wear rate of the tire when tested under controlled conditions on a specified
U.S. government course. For example, a tire
graded 150 would wear one and one-half
times as well on the government course as a tire graded 100.
The relative performance of tires depends
upon the actual conditions of their use, how-
ever, and may depart significantly from the
norm, due to variations in driving habits, ser-
vice practices and differences in road char-
acteristics and climate conditions. Traction
G
WARNING
The traction grade assigned to this tire is
based on straight-ahead braking traction
tests, and does not include acceleration, cor- nering, hydroplaning, or peak traction char-
acteristics.
The traction grades, from highest to lowest,
are AA, A, B, and C. Those grades represent
the tire's ability to stop on a wet surface as
measured under controlled conditions on
specified government test surfaces of asphalt
and concrete. A tire marked C may have poor
traction performance.
The safe speed on a wet, snow covered or icy road is always lower than on dry road surfa-
ces.
You should pay special attention to road con-
ditions when temperatures are around the
freezing point.
Mercedes-Benz recommends a minimum
tread depth of 00CFin (4 mm) for all four winter
tires (Y page 335) to maintain normal driving
characteristics in winter. Winter tires can
reduce the braking distance on snow-covered surfaces in comparison with summer tires.
Stopping distance, however, is still consider-
ably greater than when the road is not cov- Uniform Tire Quality Grading Standards
347Wheels and tires Z
Maximum load on one tire
Maximum load on one tire. This is calculated
by dividing the maximum axle load of one axle by two. PSI (pounds per square inch)
A standard unit of measure for tire pressure. Aspect ratio
Relationship between tire height and tire
width in percent. Tire pressure
This is pressure inside the tire applying an
outward force to each square inch of the tire's surface. The tire pressure is specified in
pounds per square inch (psi), in kilopascal
(kPa) or in bar. The tire pressure should only
be corrected when the tires are cold. Tire pressure of cold tires
The tires are cold:
R if the vehicle has been parked without
direct sunlight on the tires for at least three
hours and
R if the vehicle has not been driven further
than 1 mile (1.6 km) Tread
The part of the tire that comes into contact
with the road. Bead
The tire bead ensures that the tire sits
securely on the wheel. There are several steel
wires in the bead to prevent the tire from
coming loose from the wheel rim. Sidewall
The part of the tire between the tread and the
bead. Weight of optional extras
The combined weight of those optional extras that weigh more than the replaced standard
parts and more than 2.3 kg (5 lbs). These
optional extras, such as high-performance
brakes, level control, a roof rack or a high-
performance battery, are not included in the
curb weight and the weight of the accesso-
ries. TIN (Tire Identification Number)
This is a unique identifier which can be used
by a tire manufacturer to identify tires, for
example for a product recall, and thus identify the purchasers. The TIN is made up of the
manufacturer's identity code, tire size, tire
type code and the manufacturing date. Load bearing index
The load bearing index (also load index) is a
code that contains the maximum load bearing
capacity of a tire. Traction
Traction is the result of friction between the
tires and the road surface. TWR (Tongue Weight Rating)
The TWR specifies the maximum permissible
weight that the ball coupling of the trailer tow
hitch can support. 354
Definition of terms for tires and loadingWheels and tires
