BMW M COUPE, Owner'S Manual

Page: 99 / 167

99 n
Index
Data
Te
chnolog
y
Repairs
Maintenance
Controls
Overview
Tire replacement
To maintain good handling and vehicle
response, use only tires of a single
tread configuration from a single manu-
facturer. BMW tests and approves
wheel and tire specifications. Refer to
page
103 .
DOT Quality Grades
Tread wear
Traction AA A B C
Temperature A B C
All passenger vehicle tires must
conform to Federal Safety Require-
ments in addition to these grades.
<
Tread wear
The tread wear grade is a comparative
rating based on the wear rate of the tire
when tested under controlled condi-
tions on a specified government test
course.
For example, 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 condi-
tions of their use, however, and may
depart significantly from the norm due
to variations in driving habits, service
practices and differences in road char-
acteristics 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 speci-
fied government test surfaces of
asphalt and concrete. A tire marked C
may have poor traction performance.
The traction grade assigned to
this tire is based on straight-
ahead braking traction tests, and does
not include acceleration, cornering,
aquaplaning, or peak traction charac-
teristics.
<
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 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 a sudden flat
tire. The grade C corresponds to a level
of performance which all passenger
vehicle tires must meet under the
Federal Motor Vehicle Safety Standard
No. 109. Grades B and A represent
higher levels of performance on the
laboratory test wheel than the minimum
required by law.
The temperature grade for this tire
is established for a tire that is
properly inflated and not overloaded.
Excessive speed, underinflation, or
excessive loading, either separately or
in combination, can cause heat buildup
and possible tire failure.
<
Uniform Tire Quality Grading
Quality grades can be found where
applicable on the tire sidewall between
tread shoulder and maximum section
width. For example:
Tread wear 200
Traction AA
Temperature A