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INSPECTION AND MAINTENANCE
66J22-03E
C. Tire Size
The tire size code is a combination of
letters and numbers used to define a
particular tire’s width, height, aspect
ratio, construction type, and service
description. See the “Tire Size” expla-
nation later in this section for more
details.
D. U.S. DOT Tire Identification Number
The Department of Transportation
(DOT) marking indicates that the tire
is in compliance with the U.S. Depart-
ment of Transportation Motor Vehicle
Safety Standards. The letters and
numbers following the DOT marking
is the Tire Identification Number
(TIN). The TIN identifies the tire man-
ufacturer and plant, tire size, and date
the tire was manufactured.
E. Uniform Tire Quality Grading (UTQG)
Tire manufacturers are required to
grade tires based on three perfor-
mance factors: treadwear, traction
and temperature resistance. Refer to
the “Uniform Tire Quality Grading”
section for more details.
F. Load Rating
Load rating is the maximum weight a
tire is designed to support in normal
service.
G. Max Inflation Pressure
Max inflation pressure is the maxi-
mum inflation pressure a tire is
designed for.
H. Tire Ply Material
These tire markings describe the type
of cord and number of plies in the
sidewall and under the tread.
I. Load Index and Speed Rating
The two- or three-digit number is the
tire’s load index, the maximum load a
tire can carry at the speed indicated
by its speed symbol at the maximum
inflation pressure. The higher the
number is, the greater the load carry-
ing capacity. The letter symbol
denotes the speed at which a tire is
designed to be driven for extended
periods of time. (Ratings are listed
below.)
*The letters ZR may be used on tires with a
maximum speed capability over 149 mph
and will always be used on tires with a
maximum speed capability over 186 mph.
J. M+S Marking
This marking indicates the tire has
some mud and snow capabilities and
is designed for all-season use.
Tire Size
The following illustration shows an exam-
ple of a typical passenger car tire size.
67D028
A. Tire Type
This letter code indicates the primary
intended use of the tire. The letter “P”
identifies a tire primarily intended for
use on a passenger vehicle.
B. Tire Width
This three-digit number indicates the
tire section width in millimeters from
sidewall to sidewall.
C. Aspect Ratio
This two-digit number represents the
tire section height divided by the tire
section width.
Letter Rating Speed Rating
Q 99 mph
R106 mph
S112 mph
T118 mph
U124 mph
H130 mph
V149 mph
W 168 mph*
Y 186 mph*
A B C D E
EXAMPLE
Tires: 6