Tire coding, Wheels and tires – BMW Z4 Roadster 2.5i 2005 User Manual

Page 82

Wheels and tires

Tire coding

Understanding the lettering on the tire sidewall
makes it easier to identify and choose the cor-
rect tires.

Tire size

e.g.

225/50 R 16 92 V

Nominal width in mm
Cross-sectional
ratio in %
Radial belt construction
Rim diameter in inches
Load index,
not on ZR tires
Speed code letter,
in front of the R on ZR tires

Speed code letter

Q= up to 105 mph / 160 km/h
T= up to 118 mph / 190 km/h
H= up to 131 mph / 210 km/h
V= up to 150 mph / 240 km/h
W= up to 167 mph / 270 km/h
Y= up to 186 mph / 300 km/h

Tire Identification Number

Tires with DOT codes meet the guidelines of
the U.S. Department of Transportation.
DOT code:
e.g.

DOT xxxx xxx 5004

Manufacturer's code
for tire brand
Tire size and
tire version
Tire age

Tire age

The date on which the tire was manufactured is
indicated by the code on the sidewall:
DOT … 5004 indicates that the tire was manu-
factured in week 50 of the year 2004.

BMW recommends the replacement of all tires
every 6 years at the latest, even if a tire usage of
10 years is possible.

Uniform Tire Quality Grading

Quality grades can be found where applicable
on the tire sidewall between tread shoulder and
maximum section width. For example:
Treadwear 200 Traction AA
Temperature A

DOT quality grades

Tread wear
Traction AA A B C
Temperature A B C

All passenger car tires must conform to
Federal Safety Requirements 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 conditions on a specified gov-
ernment test course.
For example, a tire graded 150 would wear one
and one-half, 1

γ, times as well on the govern-

ment 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 varia-
tions in driving habits, service practices and dif-
ferences in road characteristics 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 sur-
faces 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, cor-
nering, hydroplaning, or peak traction charac-
teristics.