Us Department Of Transportation - Aston Martin DB 9 2007 Manual

Tread Wear Indicators
Tread wear indicators (A) are
incorporated into the construction of
all tires. These indicators are integral
moulded ribs spaced at regular
intervals around the circumference of
the tire and extend across the full
width of the tread, in all primary
grooves.
When a tire has worn causing one or more of the indicators
to be flush with the outer face of the tread the tire has
reached its wear limit. It then becomes illegal in certain
countries and must be replaced.

US Department of Transportation

Uniform Tire Quality Grades
The following information relates to the tire grading system
developed by the National Highway Traffic Safety
Administration, which grades tires by tread wear, traction
and temperature performance.
All passenger vehicle 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 a tire tested, under controlled conditions, on a
specified government test course. For example, a tire graded
150 would wear one and a half times (1½) 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 normal due to variations in driving
habits, service practices and differences in road
characteristics and climate.
Traction
The traction grades, from highest to lowest, are AA, A, B, and
C. The 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 performance.
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