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NHTSA Trailer Equipment Requirements
characteristics of the tire and also provides a tire
identification number for safety standard certification and
in case of a recall.
Information on Passenger Vehicle Tires
Figure 7-1. Passenger Vehicle Tires
A "P" indicates the tire is for passenger vehicles.
B This three-digit number gives the width in millime-
ters of the tire from sidewall edge to sidewall edge.
In general, the larger the number, the wider the
tire.
C This two-digit number, known as the aspect ratio,
gives the tire's ratio of height to width. Numbers of
70 or lower indicate a short sidewall for improved
steering response and better overall handling on
dry pavement.
D "R" stands for radial. Radial ply construction of
tires has been the industry standard for the past 20
years.
E This two-digit number is the wheel or rim diameter
in inches. If you change your wheel size, you will
have to purchase new tires to match the new
wheel diameter.
F (Number) This two- or three-digit number is the
tire's load index. It is a measurement of how much
weight each tire can support. You may find this
information in your owner's manual. If not, contact
a local tire dealer.
NOTE: You may not find this information on all
tires because it is not required by law.
(Letter) The speed rating denotes the speed at
which a tire is designed to be drive n for extended
periods of time. The ratings range from 99 miles
per hour (mph) to 186 mph. These ratings are
listed below.
NOTE: You may not find this information on all
tires because it is not required by law.
NOTE: See
Figure 7-1
and speed ratings.
42
014608
for complete list of letter
G U.S. DOT Tire Identification Number. This begins
with the letters "DOT" and indicates that the tire
meets all federal standards. The next two numbers
or letters are the plant code where it was manufac-
tured, and the last four numbers represent the
week and year the tire was built. For example, the
numbers 3197 means the 31st week of 1997. The
other numbers are marketing codes used at the
manufacturer's discretion. This information is used
to contact consumers if a tire defect requires a
recall.
H The "M+S" or "M/S" indicates that the tire has
some mud and snow capability. Most radial tires
have these markings; hence, they have some mud
and snow capability.
I Tire Ply Composition and Materials Used. The
number of plies indicates the number of layers of
rubber-coated fabric in the tire. In general, the
greater the number of plies, the more weight a tire
can support. Tire manufacturers also must indicate
the materials in the tire, which include steel, nylon,
polyester, and others.
J Maximum Load Rating. This number indicates the
maximum load in kilograms and pounds that can
be carried by the tire.
K Maximum Permissible Inflation Pressure. This
number is the greatest amount of air pressure that
should ever be put in the tire under normal driving
conditions.
Table 7-2. Tire Letter and Speed Rating
Letter Rating
Q
R
S
T
U
H
V
Y
NOTE: For tires with a maximum speed capability
over 149 mph, tire manufacturers sometimes use the
letters ZR. For those with a maximum speed capability
over 186 mph, tire manufacturers always use the
letters ZR.
Uniform Tire Quality Grading (UTQGS)
Quality grades can be found where applicable on the tire
sidewall between tread shoulder and maximum section
width. For example: TREADWEAR 200 TRACTION AA.
Owner's Manual for Mobile Generator Sets
Speed Rating
99 MPH
106 MPH
112 MPH
118 MPH
124 MPH
130 MPH
168 MPH
186 MPH
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