A Comprehensive Evaluation of 2001 Patrol Vehicle Tires (October 2001)


Title: A Comprehensive Evaluation of 2001 Patrol Vehicle Tires
Series: N/A
Author: NLECTC
Published: October 2001
Subject: Technology for law enforcement
pages: 9
bytes: 21KB

Figures, charts, forms, and tables are not included in this ASCII plain-text file.
To view this document in its entirety, download the Adobe Acrobat graphic file
available from this Web site or order a print copy from NLECTC at 800-248-
2742.

---------------------------
National Law Enforcement and Corrections Technology Center
A Program of the National Institute of Justice
Bulletin
October 2001

A Comprehensive Evaluation of 2001 Patrol Vehicle Tires

In July 2001, the National Law Enforcement and Corrections Technology
Center (NLECTC) of the National Institute of Justice conducted the fourth
comprehensive evaluation of patrol vehicle tires.1 This NLECTC bulletin is a
synopsis of the results from that evaluation; a detailed report is also available
that contains statistical analysis of the test data. Page 5 of this bulletin contains
information on how to obtain the report.

The major manufacturers of police tires were asked to participate and submit
samples of tires for evaluation. Four companies donated tires for testing. The
four tire brands tested were the Firestone Firehawk PV41, General XP-2000
V4, BF Goodrich Touring T/A VR4, and Goodyear Eagle RS-A. In addition to
the four "police" tires, an additional "nonpolice," or regular passenger car, tire
was evaluated. This was done in response to the many inquiries received by
NLECTC from law enforcement agencies regarding the appropriateness of
installing regular passenger car tires not specifically designed for typical law
enforcement operational use on police vehicles. Many agencies face budgetary
restrictions or other influences in the procurement process (e.g., requirements to
give local vendors priority in the procurement of goods and services) that may
require them to consider purchasing these types of tires. This nonpolice tire was
selected at random from a local tire supplier where the tests were performed.
The manufacturer of this tire does not market or make any claim that this tire is
appropriate for use on a police vehicle. For this reason, the tire is not identified
by name in this report. It is referred to as Brand X. The data presented for the
Brand X tire is for comparison purposes only and should be used only to draw
generalized conclusions about the performance of tires typically designed for
passenger car applications when compared to tires specifically designed and
engineered for use on police vehicles. The technical descriptions of these tires
may be found on page 8. 

Each brand was subjected to eight tests to measure its performance in wet and
dry road conditions and determine its tread wear characteristics. The tires were
tested on a 2001 Ford Police Interceptor and a 2001 Chevrolet Impala. These
two cars were used as test vehicles because they will represent the vast
majority of police cars in service use by law enforcement agencies during the
next 2 years. 

Because driving conditions in different parts of the country vary widely, no
specific "winners" or "losers" were identified. It is important that your
department place the appropriate weights on those portions of the test data
most representative of the conditions that you may encounter. A sample
distribution of category weights is shown in table 1.

In addition, it is important to note that the most suitable tire for an agency's
needs may depend on the make and model of the patrol vehicle on which the
tires will be used--the best tire for use on the rear-wheel-drive Ford Police
Interceptor may be different from the best tire for the front-wheel-drive
Chevrolet Impala, as these vehicles have different handling and performance
characteristics, which influence overall tire performance.

The test results may be used in two ways. First, they may be used as is to
determine the tires that best meet the needs of your department. In this case,
you should emphasize some portions of the evaluation to reflect the needs of
your department. Second, the overall test results may be used to adjust the
manufacturer's bid price for these tire brands. In each test category, the
absolute difference between a tire and the best scoring tire is divided by the
best tire's score, resulting in a "deviation factor." This factor is then multiplied by
a category weight, such as those listed in table 1, to produce a weighted
category score. The total of these weighted scores for a particular tire is then
used to adjust the tire's bid price.

Static Circle Test

Dry Pavement Surface



Objective: Determine the road-holding performance characteristics of the test
tires in a steady-state turning situation on a dry pavement surface. The course
used has a flat polished concrete surface on which a circle measuring 628.3 feet
in circumference has been marked. The driver is allowed 2 laps to accelerate
and stabilize the vehicle at the highest speed possible while remaining within the
marked lane. Once the vehicle is stabilized, the following 5 laps are timed. The
vehicle is then turned around and this process (2 warm-up laps, 5 timed laps) is
repeated in the opposite direction around the circle to account for any minor
differences in the vehicle's suspension design or setup that may favor turning in a
particular direction. The average of the 10 timed laps is used to determine the
final score for this portion of the evaluation, which is expressed in lateral G's
attained. Lateral G's are the measurement of the resistance of lateral movement
before the tire loses adhesion and the vehicle begins to slip. Deficiencies in tire
adhesion or the tendency of the tire to slip under hard, steady-state cornering
maneuvers, will result in slower speeds, longer lap times, and a relatively lower
overall score on this portion of the evaluation.

Methodology: Following a 2-lap warmup, each test vehicle equipped with the
make and model of tire to be evaluated makes a minimum of 5 timed laps
around the static circle course. The vehicle is then turned around and the
process (2 warm-up laps, 5 timed laps) is repeated in the opposite direction
around the circle. The final score for each brand of tire on this portion of the
evaluation is the average of the 10 timed laps and is expressed as lateral G's
attained. Table 2 shows the results from the dry pavement portion of the test.

Wet Pavement Surface

Objective: Determine the road-holding performance characteristics of the test
tires in a steady-state turning situation on a wet pavement surface having a
constant 3/8-inch to Ť-inch of water depth. The course used has a flat polished
concrete surface on which a circle measuring 628.3 feet in circumference has
been marked. The driver is allowed 2 laps to accelerate and stabilize the vehicle
at the highest speed possible while remaining within the marked lane. Once the
vehicle is stabilized, the following 5 laps are timed. The vehicle is then turned
around and this process (2 warm-up laps, 5 timed laps) is repeated in the
opposite direction around the circle to account for any minor differences in the
vehicle's suspension design or setup that may favor turning in a particular
direction. The average of the 10 timed laps is used to determine the final score
for this portion of the evaluation, which is expressed in lateral G's attained.
Lateral G's are the measurement of the resistance of lateral movement before
the tire loses adhesion and the vehicle begins to slip. Deficiencies in tire
adhesion, or the tendency of the tire to slip under hard, steady-state cornering
maneuvers, will result in slower speeds, longer lap times, and a relatively lower
overall score on this portion of the evaluation.

Methodology: Following a 2-lap warmup, each test vehicle equipped with the
make and model of tire to be evaluated makes a minimum of 5 timed laps
around the static circle course. The vehicle is then turned around and the
process (2 warm-up laps, 5 timed laps) is repeated in the opposite direction
around the circle. The final score for each brand of tire on this portion of the
evaluation is the average of the 10 timed laps and is expressed as lateral G's
attained. Table 3 shows the results from the wet pavement portion of the test.

Serpentine Test

Dry Pavement Surface

Objective: Determine each tire's transient response characteristics and
performance on a dry pavement surface. The course used is straight and flat
with 550 feet of asphalt and 150 feet of concrete. Pylons are set in a straight
line and spaced 100 feet apart. The approach speed is 60 mph, and the driver
is required to weave through the pylons while maintaining speed as close to the
approach speed as possible. Serious deficiencies in transient response will
result in longer elapsed times, slower speeds, and a lower overall score on this
portion of the evaluation.

Methodology: Following a 2-mile tire warmup, each test vehicle equipped with
the make and model of tire to be evaluated is driven through the serpentine
course a minimum of 15 times. The final score for each tire is the average of the
fastest 12 runs. Table 4 presents the results from the dry pavement portion of
this test. 

Wet Pavement Surface

Objective: Determine each test tire's transient response characteristics and
performance on a wet pavement surface. The course used is straight and flat
with approximately 420 feet of asphalt. Pylons are set in a straight line and
spaced 60 feet apart. The approach speed is 35 mph, and the driver is required
to weave through the pylons while maintaining speed as close to the approach
speed as possible. Serious deficiencies in transient response during wet
pavement maneuvering will result in longer elapsed times, slower speeds, and a
lower overall score on this portion of the evaluation.

Methodology: Following a 2-mile tire warmup, each test vehicle equipped with
the make and model of tire to be evaluated is driven through the serpentine
course a minimum of 15 times. The final score for each tire is the average of the
fastest 12 runs. Table 5 shows the results of the test under wet pavement
surface conditions.

Stopping Distance

Dry Pavement Surface

Objective: Determine the performance characteristics of the test tires in a
simulated "panic" stop of a patrol vehicle on a dry pavement surface. The
course used has a straight, flat, granite asphalt surface. A center lane marks
where the braking maneuvers are to be done. The approach speed is just over
60 mph. The test vehicle is in the Anti-Lock Brake System (ABS) mode when
the driver applies the brakes as close to 60 mph as possible. Both the exact
speed at brake application and the distance from brake application to complete
stop are electronically recorded. Average deceleration rate is then determined.
Deficiencies in tire adhesion will result in longer stopping distances and a
relatively lower score on this portion of the evaluation.

Methodology: Following a 1-mile tire warmup, each test vehicle equipped with
the make and model of tire to be evaluated makes a minimum of six measured
panic stops with the ABS in operation. The final score for each tire on this
portion of the evaluation is the average of the six measured stops. Table 6
presents the test results for the dry pavement portion of this test.

Wet Pavement Surface

Objective: Determine the performance characteristics of the test tires in a
simulated "panic" stop of a patrol vehicle on a wet pavement surface. The
course used has a flat, granite, asphalt surface. Pylons are set up to mark where
the braking maneuvers are done. The approach speed is just over 60 mph. The
test vehicle is in the ABS mode when the driver applies the brakes as close to
60 mph as possible. Both the exact speed at brake application and the distance
from brake application to complete stop are electronically recorded. Average
deceleration rate is then determined. Deficiencies in tire adhesion will result in
longer stopping distances and a relatively lower score on this portion of the
evaluation.

Methodology: Following a 1-mile tire warmup, each test vehicle equipped with
the make and model of tire to be evaluated makes a minimum of six measured
panic stops with the ABS in operation. The final score for each tire on this
portion of the evaluation is the average of the six measured stops. Table 7
shows the results of the tests performed under wet pavement surface
conditions.


High-Speed Handling

Objective: Determine the tire's high-speed pursuit handling characteristics and
performance on a 1.43-mile (7,553 feet) road racing type course. The course
contains high-speed curves, low-speed corners, and straightaways, and with
the exception of traffic, simulates actual pursuit conditions in the field. This
evaluation is a test of the manufacturers' success in blending the transient
response, cornering, and rapid deceleration characteristics of a tire. Serious
deficiencies in any of these critical areas will result in longer lap times and a
lower overall score on this portion of the evaluation.

Methodology: Following 2 warmup laps, each test vehicle equipped with the
make and model of tire to be evaluated is driven over the course by 3 drivers
for at least 15 timed laps. The final score for each tire will be the average of the
fastest 4 laps by each of the drivers, for a total of 12 laps. Table 8 presents the
results of this test.

Tire Wear Measurement

Objective: Determine each tire's wear characteristics when subjected to the
entire performance evaluation. Tread depth measurements are taken of the new
right front tire of each test set of each brand, model, and size of tire tested.
(New, for the purpose of this evaluation, means after a specific break-in
routine, but before any testing.) The right front tire was chosen for these
measurements because it typically exhibits the most wear in the test situations
used in this evaluation. Tread depth measurements are taken for a second time
prior to the final test phase, which is high-speed handling evaluation. Finally,
measurements are taken for a third time at the conclusion of the high-speed
handling evaluation, which completes the testing.

Methodology: Following a specific tire break-in routine, but before any testing
is done, tread depth measurements are taken of the new right front tire of each
brand, model, and size of tires tested. The measurements are taken in four
places across the tread of the tire, from outside to inside, and in four areas
around the circumference of the tire, 90 degrees apart, for a total of at least 16
measurements per right front tire. These same right front tires are once again
measured prior to the high-speed handling, and for a third time at the conclusion
of the high-speed handling, which is the final test phase, to determine the total
amount of tread depth lost during the entire test procedure. The average tread
depth total is the average of all of the individual tread depths measured on a
given tire. The final score for each tire will be the average tread depth of the
right front tire that was worn away during the testing process. Table 9 presents
the overall tire wear results.

The tire wear measurements shown in this bulletin resulted from extremely
severe operating conditions. As such, they may not be an accurate predictor of
achievable tire mileage when used in normal police patrol service, and should
not be used to extrapolate actual tire life.

This publication is also available for viewing online as text or downloading to
your computer via NLECTC's Justice Technology Information Network, or
JUSTNET, which can be found on the Internet at www.justnet.org. JUSTNET
is your information gateway, via the Internet and its World Wide Web, to
NLECTC information, products, and services as well as information on other
new technologies and equipment available to the law enforcement, corrections,
forensics, and criminal justice communities.

NLECTC would like to thank the Ford Motor Company; the Chevrolet
Division of General Motors Corporation; Bridgestone-Firestone, Inc.; General
Tire Company; Michelin America Small Tires, a division of Michelin North
America (manufacturers of the BF Goodrich tire); and Goodyear Tire and
Rubber Company for their cooperation. In addition, NLECTC greatly
appreciates the use of the First Coast Technical Center test facility at St.
Augustine, Florida, the TRW test facility in Green Cove Springs, Florida, and
the Federal Law Enforcement Training Center at Glynco, Georgia.

---------------------------

For a copy of the full tire testing report, call the National Law Enforcement and
Corrections Technology Center at 800-248-2742 or e-mail
asknlectc@nlectc.org. The center also publishes an annual report on police
patrol vehicle testing. Copies may be obtained through the same telephone
number and e-mail address.

The National Law Enforcement and Corrections Technology Center is
supported by Cooperative Agreement #96-MU-MU-K011 awarded by the
U.S. Department of Justice, National Institute of Justice. Analyses of test results
do not represent product approval or endorsement by the National Institute of
Justice, U.S. Department of Justice; Aspen Systems Corporation; or
Independent Testing & Consulting, Inc. 

The National Institute of Justice is a component of the Office of Justice
Programs, which also includes the Bureau of Justice Assistance, Bureau of
Justice Statistics, Office of Juvenile Justice and Delinquency Prevention, and
Office for Victims of Crime.


Police Tire Descriptions

The basic construction material used in all the tires was basically the same. The
tires were constructed from nylon, polyester, and steel. The tires tested on both
the Ford Police Interceptor and the Chevrolet Impala were the BF Goodrich
Touring T/A VR4, the Firestone Firehawk PV41, the General XP 2000 V4,
and the Goodyear Eagle RS A. The tire size tested was P225/60R 16. The
following are descriptions of the tires tested: [See Adobe Acrobat file for
descriptions.]

What the Descriptions Mean

All tires contain very useful information molded into the sidewall. It shows the
name of the tire, its size, whether it is tubeless or tube type, the maximum load
and maximum inflation, the important safety warning, and much other
information.

Passenger Tires

To assist in interpreting the information presented on page 8, shown here is an
artist's rendition of the sidewall of one of the tires evaluated. "P" stands for
passenger, "225" represents the width of the tire in millimeters, "60" is the ratio
of height to width, "V" is the speed rating, "R" means radial, and "16" is the
diameter of the wheel in inches. 

Some speed-rated tires carry a Service Description instead of showing the
speed symbol in the size designation. The Service Description, 97V in this
example, consists of the load index (97) and speed symbol (V).

A "B" in place of the "R" means the tire is belted bias construction. A "D" in
place of the "R" means diagonal bias construction.

The maximum load is shown in lb (pounds) and in kg (kilograms), and
maximum pressure in psi (pounds per square inch) and in kPa (kilopascals).
Kilograms and kilopascals are metric units of measurement.

The letters "DOT" certify compliance with all applicable safety standards
established by the U.S. Department of Transportation (DOT).

Adjacent to this is a tire identification or serial number. This serial number is a
code with up to 11 digits that are a combination of numbers and letters.

The sidewall also shows the type of cord and number of plies in the sidewall
and under the tread. DOT requires tire manufacturers to grade passenger car
tires based on three performance factors: treadwear, traction, and temperature
resistance.

Treadwear

The treadwear grade is a comparative rating based on the wear rate of the tire
when tested under controlled conditions on a specified government test track.

A tire graded 200 would wear twice as long on the government test course
under specified test conditions as one graded 100.

It is wrong to link treadwear grades with your projected tire mileage. The
relative performance of tires depends upon the actual conditions of their use
and may vary due to driving habits, service practices, differences in road
characteristics, and climate.

Traction

Traction grades, from highest to lowest, are A, B, and C. They represent the
tire's ability to stop on wet pavement as measured under controlled conditions
on specified government test surfaces of asphalt and concrete.

Temperature

The temperature grades, from highest to lowest, are A, B, and C. These
represent the tire's resistance to the generation of heat when tested under
controlled conditions on a specified indoor laboratory test wheel.

Source: Tire Industry Safety Council