Technical Report
Determination of Tire Energy Dissipation
Analysis and
Recommended Practices
April 1978
by
Glenn D. Thompson
Richard N. Burgeson
Notice
Technical reports are intended to present a technical analysis of an
issue and recommendations resulting from the assumptions and constraints
of that analysis. Agency policy constraints or data received subsequent
to the date of release of this report may alter the conclusions reached.
Readers are cautioned to seek the latest analysis from EPA before using
the information contained herein.
Standards Development and Support Branch
Emission Control Technology Division
Office of Mobile Source Air Pollution Control
Office of Air and Waste Management
U.S. Environmental Protection Agency

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Abstract
The vehicle tire has a very significant effect on the fuel consumption
of the vehicle. For example, during low speed operation the tire is the
major source of external energy dissipation by the vehicle. Because of
the large effects of the tires and because significant variations have
been observed among tires, it is important that the vehicles used for
EPA fuel economy measurements be equipped with appropriate tires.
As an initial step to insure test vehicles are equipped with appropriate
tires, EPA issued Advisory Circular AC-55A to require tire information
for those vehicles for which an alternate dynamometer power absorption
was requested. This Advisory Circular stated that requiring such tire
information, as type, size, manufacturer, sidewall cord materials, belt
material, and the number of sidewall and belt plies was an interim
approach until a standardized, acceptable test procedure for determining
tire energy dissipation was available.
This report analyzes the currently available methods and test equipment
for determining tire energy dissipation. It is concluded that a fully
transient procedure is preferred, however such a procedure could not be
conducted on equipment in current widespread use. It is however, feasible
to conduct thermally transient measurements on free rolling tires with
the prevailing equipment. Consequently, a Recommended Practice for the
Determination of Tire Energy Dissipation -Quasi Steady State Procedure
is provided as Appendix A of this report. In addition, a preferred,

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Recommended Practice for Determination of Tire Energy Dissipation -
Transient Procedure is provided as Appendix B.

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Determination of Tire Energy Dissipation
I.	Purpose
This report presents test procedures for the determination of tire
energy dissipation information. The determination of tire energy dissipation
information will enable more appropriate, realistic testing of vehicles
for both exhaust emissions and fuel economy measurements. The decisions
made in developing these test procedures for determination of tire
energy dissipation are documented in this report.
II.	Background
During low speed operation, the tire is the major source of energy
dissipation by the vehicle. Consequently, the vehicle tire has a very
significant effect on the fuel consumption and emissions (especially
oxides of nitrogen) of the vehicle.
A recent experimental effort reported variations in tire rolling resistance
with respect to tire type, tire size, and tire manufacturer. (1)*
Consequently, to improve exhaust emissions and fuel economy tests, EPA
issued Advisory Circular AC 55A to require tire information for those
vehicles for which an alternate dynamometer power absorption was requested.
This Advisory Circular stated that requesting such tire information as
* lumbers within parenthesis designate references given at the end
of the paper.

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type, si^e, manufacturer, sidewall cord materials, belt material, and
the number of sidewall and belt plies, was an interim approach until a
standardized, acceptable test procedure for determining tire energy
dissipation was available.
III. Discussion
The development of a laboratory test procedure to simulate the "real
world" experience of some device always represents compromises between
the simulation accuracy and the test expediency. The decisions in these
areas must, of course, depend on the purpose the user intends for the
resulting information. This section presents the questions which arose
during the development of the EPA recommended practices for tire energy
dissipation determination and the decisions which were made. The subsequent
sections present the actual recommended procedures for tire energy
dissipation determination.
A. Applications for Tire Energy Dissipation Information
Tire energy dissipation information is desired for the following reasons:
- Support of the EPA exhaust emission certification and fuel economy
measurement programs;-
To provide direction, incentive, and reward for the production of
low energy dissipation tires; and

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To provide public information and guidance on the fuel economy
effects of tire selection.
The information necessary to support the EPA exhaust emission and fuel
economy measurements is the most important and immediate need for EPA.
During the EPA tests the vehicle tires dissipate approximately 30
percent of the energy delivered to the vehicle wheels. The choice of
tires installed on the EPA test vehicles and on the production vehicles
is presently virtually uncontrolled.* By comparison, test vehicle
inertia simulation and the dynamometer power absorption each have approx-
imately the same effect on the vehicle energy dissipation over the
composite of the two cycles as do the vehicle tires. Each of these two
parameters, however, is controlled to approximately + 3 percent.
EPA awareness or control of tire selection for the test vehicles is only
important if variations exist among tires. This has been investigated
and average differences of approximately 25 percent were observed between
tire types. Within tire types, significant variations by manufacturers
were observed as were variations by tire size. (2)
The second reason for EPA interest, to provide incentive and reward for
the use of low energy dissipation tires is of major importance, but not
quite the same immediate concern as the previous reason. This incentive,
at least for OEM tires, already exists in the fuel economy standards.
* Some control does exist over tire selection in the case of vehicles
using requested alternate dynamometer power absorptions. However,
even this control is based on such paraneters as tire type, size,
manufacturer, etc., and does not directly consider the tire energy
dissipation.

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The important aspect is to focus the tire development efforts toward
improved tire performance for the consumer.
The third reason, to provide public information and guidance on the fuel
economy effects of various tires, is probably the most important long
range goal. This area is extremely important for fuel conservation
because of the important role of the tire on fuel consumption, and since
approximately 80 percent of all tires sold are aftermarket replacement
tires. Even with the potential national importance, this goal must be
considered as secondary for EPA compared to supporting current programs.
The important aspect is to avoid EPA actions or decisions which might
compromise this long range objective.
B. Tire Test Approaches
Practices for tire testing range from energy dissipation measurements
under steady state free rolling conditions to measurements under conditions
which simulate the tire experience on the vehicle. The major difference
is that simulation of the tire experience on a vehicle must involve
transient conditions and transmitted forces which are not present in the
simpler steady state practices. The following chart outlines the transient
versus steady state differences.

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Steady State	Vehicle Simulation
Wanned up tire	Initially cold tire, tire temperature increases
during the test
Constant inflation pressure Inflation pressure increases as the tire
temperature increases
Free rolling tire	Forces transmitted by the tire (driving
and braking)
Steady speed	Transient speeds
In addition to the transient versus steady state question, the question
of a dynamometer roll or wheel versus a flat surface belt type test
machine must be considered. All of these areas will be discussed in the
following sections.
1. Initially Cold Tire vs. Warmed Up Tire
Tire energy dissipation significantly decreases as the tire warms up, as
shown in Figure 1. (3) This effect occurs for two reasons. As the tire
warms up, the temperature of the contained air increases, which results
in an increase in inflation pressure and a subsequent decrease in the
tire deflection. In addition, the rubber hysteresis decreases with
increasing temperature, therefore the energy dissipation for a given
deflection also decreases with increasing tire temperature.
Any tire test which attempts to simulate vehicle use must start with a
cold tire. Depending on the length of the test period, a temperature
transient test procedure may have the advantage of requiring less total
test time than measurements on a tire at thermal equilibrium since

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Time (seconds)
Figure 1 - Typical Tire Energy Dissipation
Force vs. Time

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light-duty vehicle tires require approximately 30 minutes to reach
thermal equilibrium.
The disadvantage of the thermally transient test is that multiple or
continuous data sampling is required during the test. Also, the thermal
experience of the tire prior to the test becomes a significant factor in
the test results.
The thermally transient cycle is considered preferred for the EPA
recommended practice because of the improved simulation of the normal
tire experience. For example, considering the data of Figure 1, the
tire energy dissipation at thermal equilibrium is about 20 percent lower
than the average tire energy dissipation over the first 20 minutes of
the hire operation.
2. Inflation Pressure Build vs. Constant Inflation Pressure
This question is strongly related to the transient temperature question
since the temperature effect is primarily a temperature-pressure effect.
If simulation of the tire experience on the vehicle is important, then
the effects of the inflation pressure increase with increasing tem-
perature must be considered. As in the previous case, no major dis-
advantages are incurred with a test practice of this nature, therefore
this is considered to be the preferred method. Separation of this
effect into individual temperature and pressure effects is difficult and
is artificial since the separation does not occur during consumer vehicle
use.

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3. Forces Transmitted by the Tire vs. the Free Rolling Tire
When the tire is used on a vehicle, all tires often transmit negative
(braking) forces. In addition, the drive tires must transmit the
positive drive forces.
Unfortunately, measuring the tire energy dissipation for a tire under
tractive effort is considerably more difficult than measurements on a
free rolling tire. This difficulty occurs because the transmitted
tractive forces are much greater than the tire energy dissipation forces.
In effect two large quantities, the input force and the output force,
must both be measured and then subtracted to obtain the small difference
which is the tire energy dissipation. For example, the force necessary
to maintain a vehicle at a steady 50 mph are typically 100 to 150 pounds
at the road-drive tire interface. During accelerations the forces may
approach 1000 pounds. By comparison the drive tire dissipation forces
would typically be 30 pounds.
Because of the greater difficulty in performing tire energy dissipation
measurements on tires transmitting forces, few facilities exist which
can conduct such tests. Consequently, there is very little information
in the literature on tire energy dissipation during force transmission.
However, limited data reported by Calspan for a single tire indicates
that tire energy dissipation increases as the tractive effort of the
tire increases. (4) A plot of these data is presented in Figure 2. In
general, this is to be expected since the tire undergoes greater deformation

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Transmitted Longitudinal Force (lb)
Figure 2 - Tire Energy Dissipative
Force is Transmitted Force

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when transmitting high forces and this deformation must result in greater
tire energy dissipation. Consequently, energy dissipation measurements
on free rolling tires probably underestimate the on-road tire energy
dissipation. In addition, there is reason to believe that tires with
different construction parameters, such as ply angle, or different cord
materials, may behave differently when transmitting force. (5)
In general, measurements of tire energy dissipation when the tire is
transmitting force would be the preferred test method. However, at the
present time this is not considered practical for most test facilities.
A. Transient Speed vs. Steady Speed
In typical consumer use, vehicle tires are operated in speed transient
modes. Therefore, from the vehicle simulation standpoint, a speed
transient test is desired. The forces responsible for tire energy
dissipation are, however, relatively speed independent, at least for
moderate speeds. (6) Therefore, there is reduced need for a speed
transient cycle to consider direct speed induced effects on the tire
rolling resistance. The tire power dissipation however does increase
with speed since the power is the product of the force and velocity.
Therefore the rate of energy dissipation and the rate at which heat is
generated in the tire does.increase with vehicle speed. Consequently,
the thermal experience of the tire may be speed dependent even if the
forces are not.

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The speed transient experience of tires in consumer use is primarily
important because the drive tires are the vehicle mechanism for generating
the transient vehicle speeds and this requires the tires to transmit
large forces. Consequently, for a tire test procedure, a speed transient
cycle is primarily important if this is used as a method of requiring
the tire to transmit large forces. Therefore, the question of a speed
transient cycle for a tire test is really the same as the previous
question of tire force transmission.
A speed transient test, with mechanical inertia simulation, does have
some advantages as an approach for generating transmitted forces. The
primary advantage is that the inertia system is basically energy "conservative".
That is, energy supplied by the tire to accelerate the flywheels will be
returned to the tire during deceleration. Consequently only the net
energy supplied to the tire must be measured and the load forces supplied
to the test machine-by the inertia simulation need not be monitored. In
effect the flywheel approach eliminates the need to measure two large
quantities and compute a difference. Consequently only one transducer
need be calibrated with great precision. Even here some reduction in
transducer precision may be tolerable as long as the response is symmetric
in traction and braking. The only disadvantage is that the flywheel
bearing losses must be known to compensate for the measured energy
dissipation.
The mechanical flywheel, speed transient approach is the preferred
approach since this method requires the tire to transmit tractive

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force, correctly simulates the rate of energy dissipation during consumer
use and appears to have potential test machine advantages.
5. Flat Bed vs. Dynamometer Wheel
The final question is the advantages of a flat bed test machine versus a
cylindrical test wheel.
The flat bed has the obvious advantage of being the logical equivalent
of the road surface. There are also significant engineering advantages
to a flat belt test machine. The major advantage is that the tire
energy dissipation is different on a flat surface versus a cylindrical
surface. Consequently, correction factors must be used to compare data
from curved surface test machines to flat surface results. (7) Also,
conversion factors must be used to compare data from curved surface
machines of different diameters or even to compare curved surface data
collected by different types of transducers, i.e., torque versus force
sensors. These correction factors are, on the average, reasonably
accurate for a large collection of tires. However, they may not be
precisely accurate for any given tire. Consequently, tires may rank
differently for different cylindrical surface test machines. Conversely,
however, all flat bed machines should, at least, rank tires in the same
order.
The disadvantages of a flat bed machine are their cost and availability.
Only one such device, the Calspan facility, is currently commercially

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active. A smaller flat bed test facility, the prototype for the Calspan
machine, exists at the University of Pennsylvania. In addition, General
Motors has a flat bed tire test facility currently under construction.
Even though the flat bed approach is the preferred method, the limited
availability of these test machines precludes extensive use of this type
of tire test apparatus in the near future.
IV. Conclusions
The preferred tire test procedure should be thermally transient, require
the tire to transmit torque, and should be conducted on a flat test
surface. However, wide usage of such a procedure is not practical at
the current time because of test facility limitations.
Since EPA has a definite, immediate need for tire energy dissipation
information,a recommended practice for obtaining this information on
available facilities is necessary. The capability limitations of those
facilities which are widely available at this time preclude measurements
on tires which are transmitting force. Therefore a simpler procedure
which can be performed in the majority of the existing facilities should
be considered. This procedure should be a thermally transient, steady
state speed measurement of free rolling tire energy dissipation on a
cylindrical test machine. It is concluded that such an approach can
yield useful information, at least, when comparing tires tested at one
facility. A recommended practice of this nature is presented as Appendix
A of this report.

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It is also concluded that there are potential problems in any procedure
which only considers free rolling tires on a cylindrical surface. For
this reason data collection by more preferred procedures should be
encouraged. Consequently, a recommended practice for determination of
tire energy dissipation when the tires are transmitting forces to a flat
surface should be provided for eventual use. This fully transient test
procedure is presented as Appendix B of this report.

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References
1.	G-D. Thompson and M. Torres, "Variations in Tire Rolling Resistance"
EPA Technical Support Report for Regulatory Action. October 1977.
2.	IBID
3.	D.J. Schuring, "Rolling Resistance of Tire Measured Under Transient
and Equilibrium Conditions on Calspans Tire Research Facility",
Final Report to U.S. Department of Transportation, Office of Systems
Development and Technology under Contract DOT-TSC-OST-76-9, March 1976.
4.	IBID
5.	I. Gusakotf, telephone conversation.
6.	G.D. Thompson, "Light-Duty Vehicle Road Load Determination", EPA
Technical Support Report for Regulatory Action, April 1977.
7.	S.K. Clark, "Rolling Resistance Forces in Pneumatic Tires", Interim
Report prepared for the U.S. Department of Transportation, Transporation
Systems Center under Contract D0T-TSC-1031, January 1976.

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Appendix A
Recommended Practice for Determination of Tire Energy
Dissipation - Quasi Steady State Procedure

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This recommended practice provides a procedure to determine tire energy
dissipation for a free rolling tire at primarily steady state speed but
considering the thermally transient nature of the energy dissipation
during the tire warm up.
A. Test Dynamometer Requirements
The test dynamometer shall be a large diameter (greater than 1 m)
cylindrical surface machine. The test machine shall be capable of
supplying a force on the tire perpendicular to the test surface and be
able to measure the torques required to rotate the tire. During this
process the machine must be capable of maintaining a constant speed, and
capable of measuring this speed and the peripheral distance traveled by
the .test surface.
1.	Vertical force - The test machine shall be capable of imposing
constant forces between 2000 nt and 8000 nt on the tire perpendicular to
the test surface. The machine shall be capable of maintaining the load
on tire constant to within + AO nt and shall be capable of measuring
this load to within +10 nt.
2.	Tire Dissipation Forces - The test machine shall be capable of
measuring the torques required to rotate the test tire to within +
2 nt-m (1 ft-lb).
3.	Test Speed - The machine shall be capable of maintaining the desired
test speed to within + 1 m/sec (2 mi/hr) and shall be capable of measuring

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this speed to within +0.1 m/sec. (0.2 mi/hr)
4.	Loaded Radius - The test machine shall have a method of measuring
the loaded radius of the tire; that is, the perpendicular distance from
the axis of rotation of the tire to the test surface. This distance
measurement shall be accurate to within + 1 mm (+0.05 in.)
5.	The Test Surface - The test surface of the machine shall be a
bonded abrasive aggregate of approximately number 80 grit.
B. The Test Cell Requirements
The requirements for the test cell, is that the ambient temperature be
well~controlled. In addition, the support services of compressed air
should be available for tire inflation as should the necessary gauges to
measure tire inflation.
1.	Temperature - The temperature in the test cell and in any area used
to store the tire within four hours prior to testing shall be maintained
at 20C + 2C (68F + 4F).
2.	Tire Inflation Pressure Gauges - The gauges used to measure the
tire inflation pressures shall be accurate to within +0.5 kPaG (+ 0.07
psi) .

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C- Test Procedure
The test procedure consists of the following steps:
-	Tire break-in
-	Equilibration of the tire to the test ambient temperature
-	Installation of the tire on the test machine
Operation of the tire over the test cycle
1.	Tire Break-In - The test tires shall be mounted on appropriate rims
and shall be operated for a minimum of 100 km and a maximum of 500 km
prior to testing. An appropriate rim is one of an approved contour and
width as specified for the test tire in the current yearbook of the Tire
and Rim Association Inc. The tire break-in may be conducted with a
vehicle on a road or track surface, or may be accumulated on the tire
test machine. During the break-in period, the compressive load on the
tire shall be at least 80% of the maximum design load of the tire.
2.	Equilibration to the Test Temperature - After tire break-in the
tire shall be stored in an environment of 20C + 2C for a minimum of
four hours preceeding the test. During this period the tire inflation
pressure should be checked and adjusted if necessary to the cold inflation
pressure for the test. The test inflation pressures shall be the
appropriate design cold inflation pressures specified in the current

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Yearbook of the Tire and Rim Association Inc. for the tire size and
load. Any adjustment of the inflation pressure should occur approx-
imately one hour before the test period to provide adequate time for any
air introduced into the tire to reach the equilibrium temperature.
3.	Installation on the Test Machine - The tire shall be installed on
the test machine and the load on the tire perpendicular to the test
surface shall be adjusted to 80% of the maximum design load of the tire,
for the test pressure. The alignment of the loaded tire shall be:
Perpendicular to the test surface + 1
Slip angle 0+0.25
- Camber angle 0 + 0.50
At this time the inflation pressure of the tire shall be checked and
recorded. The tire inflation pressure may be adjusted, up to a maximum
adjustment of 10 kPa (1.5 psi) at this time. Tire inflation shall be
correct to within + 1 kPa (0.15 psi)
4.	Operation Over the Test Cycles - The test machine shall be accelerated
from rest to the test speed of 10 m/sec at the approximate rate of 1
2
m/sec . The test speed of 10 m/sec shall be maintained for 1,200 seconds
(20 min.), after which the tire shall be brought to a stop with a deceleration
2
rate of approximately 1 m/sec . A graphical representation of this test
cycle is given in the attachment of this appendix.

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The tire shall then be allowed to remain at rest on the test machine for
600 seconds (10 minutes).
After completion of the 10 minute stationary phase the tire shall be
2
accelerated from rest to a speed of 20 m/sec at the rate of 1 m/sec .
The test speed of 20 m/sec shall be maintained for 800 seconds (13.33
minutes) after which the tire shall be brought to a stop with a deceleration
rate of 1 m/sec. A graphical representation of this test cycle is
included in the attachment of this Appendix.
During all steady speed test phases the torques necessary to rotate the
tire and the velocities of the test surface shall be measured. These
data shall be recorded, preferably each second, but a minimum frequency
of once every five seconds is acceptable.
D. Data Analysis
The data analysis consists of three steps, computation of the total
energy required for each cycle, subtraction of the energy dissipation
from the residual friction of the test machine to determine the net tire
energy dissipation and finally the computation of an energy dissipation
coefficient.
1. Computation of the Total Energy Dissipation - The torque necessary
to drive the tire shall be multiplied by the angular velocity of this
shaft transmitting the drive torque to determine the instantaneous
power. That is:

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P. = T .0).
i 11
where:	= the power dissipated during the	time interval
= the torque measured during the i*"*1 time interval
= the angular velocity during the i*"*1 time interval
The instantaneous powers shall then be multiplied by the sample time
period and summed to give the total energy dissipation over each test
cycle:
E = E p.t.
s .11
l
where:
Eg = the total system energy dissipation
t^ = the length of the i^ time interval
2. The Tire Energy Dissipation - The tire energy dissipation shall be
calculated from the total system energy by subtraction of the energy
dissipation caused by the mechanical friction of the system. That is:
E = E - E
t s f
where:
E^ = the tire energy dissipation
= the energy dissipation caused by friction in the test machine
during the test cycle.

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The methods used to determine E^ will depend on the specific design of
the test machine. The quantity E^ should, of course, only include those
friction losses which were included in the measurement of E . If the
s
quanity varies with time during the test cycle this variation must be
considered,
A specific energy dissipation coefficient can now be computed from the
tire energy dissipation of each cycle by dividing this quantity by the
total distance the test surface traveled and by the load on the tire
perpendicular to this surface.
e = Efc/LD
where:
e = specific energy dissipation coefficient
L = the load on the tire normal to the test surface
D = the distance traveled by the test surface
It should be noted that e is a dimensionless coefficient and is equivalent
to the average rolling resistance coefficient over the test cycle.

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Attachment
to
Appendix A
Graphical Representation
of the Quasi Steady State Cycles

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20
Speed
(m/scc)
10
1200 second
low speed
segment
0
800 second
high speed
segment
600 second
"rest"
time
Graphical Representation of
the Quasi - Steady State Cycles

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Appendix B
Recommended Practice for Determine Hon of Tirp
Energy Dissipation - Transient Procedure

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This recommended practice provides a procedure to determine tire energy
dissipation under transient conditions. This recommended practice
closely simulates the tire experience on consumer vehicles. Conse-
quently it considers both driving tires exerting tractive forces and
non-driving or free rolling tires. The EPA driving cycles are chosen as
test cycles representative of consumer vehicle use.
A. Test Dynamometer Requirements
The tire test machine (dynamometer) should be a flat belt machine which
can accommodate two tires, one tire representing the vehicle driving
tire and one representing the non-driving tire. Each tire shall receive
a force normal to the test surface which is equivalent to 80% of its
load rating. The system should be driven by driving one tire, the
"driving tire" such that the peripheral velocity of the test surface
corresponds to the EPA driving schedules. Graphical plots and speed
versus time listings for each of the driving schedules are provided as
an attachment to this recommended practice. The torque or force requirement
of the driving tire shall be measured during each second of the driving
schedules. The tire forces and the instantaneous velocity of the test
surface shall be recorded throughout the cycle.
1. Vertical force - The test machine shall be capable of imposing
constant forces between 2000 nt and 8000 nt on the tire perpendicular to
the test surface. The machine shall be capable of maintaining the load
on tire constant to within + 40 nt and shall be capable of measuring
this load to +10 nt.

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2. Tire Dissipation Forces - The test machine shall be capable of
measuring the forces required to drive the test tire to within + 1 nt.
3- Test Speed - The machine shall be capable of maintaining the
desired test schedule speed to within + 1 m/sec (2 mi/hr) and shall be
capable of measuring this speed to within +0.1 m/sec- (0.2 mi/hr)
4.	Inertia Simulation - The tire test dynamometer shall be adjusted to
apply an inertia simulation appropriate for a vehicle with a mass equivalent
to the total normal load upon the test tires. That is, of the available
increments of simulated inertial mass, that simulated inertia which is
nearest to the total normal load force on the tires divided by the
2
gravitational constant (9.80m/sec ) shall be selected.
The inertia increments shall be 50 kg or less and the accuracy of the
inertial simulation shall be within + 1 kg of the selected inertia.
5.	Loaded Radius - The test machine shall have a method of measuring
the loaded radius of the tire; that is, the perpendicular distance from
the axis of rotation of the tire to the test surface- This distance
measurement shall be accurate to within + 1 mm (+0.05 in.)
6.	The Test Surface - The test surface of the machine shall be a
bonded abrasive aggregate of approximately number 80 grit.

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B. The Test Cell Requirements
The requirements for the test cell, is that the ambient temperature be
well controlled. In addition, the support services of compressed air
should be available for tire inflation as should and the necessary
gauges to measure tire inflation.
1.	Temperature - The temperature in the test cell and in any area used
to store the tire within four hours prior to testing shall be maintained
at 20C + 2C (68F + 4F).
2.	Tire Inflation Pressure Gauges - The gauges used to measure the
tire inflation pressures shall be accurate to with +0.5 kPa (0.07 psi).
C. Test Procedure
The test procedure consists of the following steps:
-	Tire break-in
-	Equilibration of the tire to the test ambient temperature
-	Installation of the tire on the test machine
-	Operation of the tire over the test cycle

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1.	Tire Break-In - The test tires shall be mounted on appropriate rims
and shall be operated for a minimum of 100 km and a maximum of 500 km
prior to testing. An appropriate rim is one of an approved contour and
width as specified for the test tire in the current yearbook of the Tire
and Rim Association, Inc. The tire break-in many be conducted with a
vehicle on a road or track surface, or may be accumulated on the tire
test machine. During the break-in period, the vertical load on the tire
shall be at least 80% of the maximum design load of the tire.
2.	Equilibration to the Test Temperature - After tire break-in the
tire shall be stored in an environment of 20C + 2C for a minimum of
four hours preceeding the test. During this period the tire inflation
pressure should be checked and adjusted if necessary to the cold inflation
pressure for the test. The test inflation pressures shall be the appropriate
design cold inflation pressure specified in the current Yearbook of the
Tire and Rim Association, Inc. for the test tire size and load. Any
adjustment of the inflation pressure should occur prior to the last hour
of the temperature equilibration period to provide adequate time for any
air introduced into the tire to reach the equilibrium temperature.
3.	Installation on the Test Machine - The tire shall be installed on
the test machine and the load on the tire perpendicular to the test
surface shall be adjusted to 80% of the maximum design load of the tire.
The alignment of the loaded tire shall be:
Perpendicular to the test surface + 0.30
Slip angle 0 + 0.25

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Camber angle 0 + 0.50
At this time the inflation pressure of the tire shall be finally checked
and recorded. The tire inflation pressure may be adjusted up to a
maximum of 10 kPa (1.5 psi) at this time. Tire inflation pressure shall
be correct to within + 1 kPa (0.15 psi)
A. Operation Over the Test Cycles -
a.	The tires shall be operated over the cold transient portion of
the EPA urban driving schedule (the first 505 seconds).
b.	The tire shall be operated over the hot stabilized portion of
the EPA urban driving schedule (from the 505 to the 1371 second
points).
c.	The tires shall be allowed to "rest" on the test machine for
10 minutes and then the first 505 seconds of the EPA urban cycle
shall be repeated. This is the hot transient segment of the test.
d.	After completion of the second 505 seconds of the EPA urban
cycle the tires shall be immediately operated over the EPA Highway
Fuel Economy Cycle.
During all dynamic test phases the force necessary to drive the tire
shall be monitored as shall the velocities of the test surface. These
data shall be recorded, each second.

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D. Data Analysis
The data analysis consists of three steps, computation of the total
energy required for each cyle, substraction of the energy dissipation
from the residual friction of the test machine to determine the net tire
energy dissipation and finally the computation of an energy dissipation
coefficient.
1. Computation of the Total Energy Dissipation  The force necessary
to drive the tire shall be multiplied by the test surface velocity to
determine the instantaneous power. This is:
p. = f.v.
i 11
where:
p^ = the power required during the i interval
f^ = the force measured during the i interval
v. = the velocity of the i interval
l
The instantaneous powers shall then be multiplied by the sample time
period and summed to give the total energy dissipation over each test
cycle:

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where:
Eg = the total system energy dissipation
t_^ = the length of the i*"*1 time interval
2. The Tire Energy Dissipation - The tire energy dissipation shall be
calculated from the total system energy by subtraction of the energy
dissipation caused by the mechanical friction of the system. That is:
E = E - E.
t s f
where:
E^ = the tire energy dissipation
E^ = the energy dissipation caused by friction in the test machine
during the test cycle.
The methods used to determine E^ will depend on the specific design of
the test machine. The quantity E^ should, of course, only include those
friction losses which were included in the measurement of E . If the
s
quantity E^ varies with time during the test cycle, this variation must
be considered.

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A weighted average energy dissipation coefficient can now be computed
for the urban cycle by dividing the total tire energy dissipation by
the total distance the test surface traveled and by the total load on
the tires perpendicular to this surface.
eu - -43 Ist)Ll
+ 0.57	+ Est)/(Dhe + Dst)L]
where:
ey = specific energy dissipation coefficent for the urban cycle
E = the tire energy dissipated over the initial segment of the
urban test cycle (4a)
E =	the tire energy dissipated over the second test segment of the
urban cycle (4b)
D =	the distance traveled during the initial segment of the urban
test cycle (4d)
D = the distance traveled during the second segment of the urban
S 
cycle. (4b)
the total load on both tires normal to the test surface

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the tire energy dissipated over the repeat of the first urban
test segment (4c)
=	the distance traveled over the repeat of the fii*st urban test
segment (4c)
0.43 and 0.57 are the weighting factors representing 43 percent of all
urban trips as starting with initially cold tires and 57 percent of
urban trips starting with warm tires.
It should be noted that is a dimensionless coefficient and is equivalent
to the average rolling resistance coefficient over the urban test
cycle.
An average energy dissipation coefficient can be computed for the
highway cycle in a similar, but simpler manner. This energy dissipation
coefficient is:
% " Ehw/DhwL
where:
e^ =	the energy dissipation coefficient for the highway cycle
=	the energy dissipation over the EPA highway cycle
=	the distance traveled over the highway cycle

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L =
the total load on both tires normal to the test surface
The energy dissipation coefficients for the two cycles can be harmonically
averaged to yield a composite energy dissipation coefficient. The
composite energy dissipation coefficient is given by:
	1	
ec	0.55 0.45
%
where:
e^ =	the composite energy dissipation coefficient
0.55 and 0.45 are the weighting factors based on 55 percent of all
mileage represented by the urban cycle and 45 percent of all mileage
represented by the highway cycle.

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Attachment to
APPENDIX B
EPA Urban and Highway Fuel
Economy Driving Schedules

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