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Wheels and tires, All about wheels and tires – Mercedes-Benz SL-Class 2014 Owners Manual User Manual

Page 591

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All about wheels and tires

Uniform Tire Quality Grading

Standards

Overview of Tire Quality Grading

Standards

Uniform Tire Quality Grading Standards are

U.S. government specifications. Their

purpose is to provide drivers with uniform

reliable information on tire performance data.

Tire manufacturers have to grade tires using

three performance factors: treadwear

grade :, traction grade ; and temperature

grade =. These regulations do not apply to

Canada. Nevertheless, all tires sold in North

America are provided with the corresponding

quality grading markings on the sidewall of

the tire.
Where applicable, the tire grading

information can be found on the tire sidewall

between the tread shoulder and maximum

tire width.
Example:

R

Treadwear grade: 200

R

Traction grade: AA

R

Temperature grade: A

All passenger car tires must conform to the

statutory safety requirements in addition to

these grades.

i

The actual values for tires are vehicle-

specific and may deviate from the values in

the illustration.

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,

however, and may depart significantly from

the norm, due to variations in driving habits,

service practices and differences in road

characteristics 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,

cornering, hydroplaning, or peak traction

characteristics.

!

Avoid wheelspin. This can lead to damage

to the drive train.

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

surfaces.
You should pay special attention to road

conditions when temperatures are around

freezing point.
Mercedes-Benz recommends a minimum

tread depth of ã in (4 mm) on all four winter

tires. Observe the legally required minimum

tire tread depth (

Y

page 577). Winter tires can

reduce the braking distance on snow-covered

surfaces in comparison with summer tires.

The braking distance is still much further than

All about wheels and tires

589

Wheels

and

tires

Z