Porsche Cayenne 2005 Owner's Manual page 270

Uniform Tire Quality Grading
Quality grades can be found where applicable on
the tire sidewall between tread shoulder and max-
imum section width.
270
Practical Tips, Minor Repairs
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Example
All passenger car tires must conform to Federal
Safety Requirements in addition to these grades.
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Treadwear
The treadwear grade is a comparative rating
based on the wear rate of the tire when tested un-
der controlled conditions on a specific govern-
ment test course. For example, a tire graded 150
would wear one and a half (1-1/2) times as well on
the government course as a tire graded 100. The
relative performance of tires depends upon the ac-
tual conditions of their use, however, and may de-
part significantly from the norm due to variations
in driving habits, service practices and differences
in road characteristics and climate.