BMW XM Owner's Manual page 341

Uniform Tire Quality Grading
Quality grades can be found where applicable
on the tire sidewall between tread shoulder
and maximum section width.
E.g.: Treadwear 200; Traction AA; Tempera-
ture A
DOT Quality Grades
Treadwear
Traction AA A B C
Temperature A B C
All passenger vehicle tires must conform to
Federal 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 gov-
ernment test course. E.g., a tire graded 150
would wear one and one-half, 1 g, 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, service
practices and differences in road characteris-
tics and climate.
Traction
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 specified 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 braking traction tests,
and does not include acceleration, cornering,
hydroplaning, or peak traction characteristics.
Online Edition for Part no. 01405A8A608 - VI/23
Wheels and tires
Temperature
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 conditions
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. The grade C corresponds
to a level of performance which all passenger
car tires must meet under the Federal Motor
Vehicle Safety Standard No. 109. Grades Band
A represent higher levels of performance on
the laboratory test wheel than the minimum
required by law.
Warning
The temperature grade for this tire is estab-
lished for a tire that is properly inflated and
not overloaded. Excessive speed, underinfla-
tion, or excessive loading, either separately
or in combination, can cause heat buildup
and possible tire failure.
M+S
Winter tires, as well as all-season tires with
better winter performance than summer tires,
can be identified by the M+S marking on the
tire side wall.
Tire tread
Safety information
Warning
If the tire tread depth is too low, driving safety
may be impaired in critical situations such as
aquaplaning or slush on the road. There is
a risk of accident. The tire tread depth may
not fall below 0.12 in/3 mm for summer tires
MOBILITY
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