NATIONAL BUREAU OF STANDARDS REPORT

10 010

EXAMINATION OF

MILEAGE MEASURING DEVICES

(Prelim inary Report of a Manual for Weights and

Measures Officials)

<NB^>

U.S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
NATIONAL BUREAU OF STANDARDS

The National Bureau of Standards1 was established by an act of Congress March 3, 1901. The Bureau's overall goal is to strengthen and advance the Nation’s science and

technology and facilitate their effective application for public benefit. To this end, the Bureau conducts research and provides: (1) a basis for the Nation's physical measure- ment system, (2) scientific and technological services for industry and government, (3) a technical basis for equity in trade, and (4) technical services to promote public safety.

The Bureau consists of the Institute for Basic Standards, the Institute for Materials Research, the Institute for Applied Technology, the Center for Computer Sciences and

Technology, and the Office for Information Programs.

THE INSTITUTE FOR BASIC STANDARDS provides the central basis within the United States of a complete and consistent system of physical measurement: coordinates

that system with measurement systems of other nations: and furnishes essential services leading to accurate and uniform physical measurements throughout the Nation’s scientific community, industry, and commerce. The Institute consists of a Center for Radiation Research, an Office of Measurement Services and the following divisions: Applied Mathematics—Electricity—Heat—Mechanics—Optical Physics—Linac

Radiation2—Nuclear Radiation 2—Applied Radiation 2—Quantum Electronics3 —

Electromagnetics3—Time and Frequency3—Laboratory Astrophysics3 —Cryogenics3

. THE INSTITUTE FOR MATERIALS RESEARCH conducts materials research lead- ing to improved methods of measurement, standards, and data on the properties of

well-characterized materials needed by industry, commerce, educational institutions, and

Government; provides advisory and research services to other Government agencies;

and develops, produces, and distributes standard reference materials. The Institute consists of the Office of Standard Reference Materials and the following divisions: Analytical Chemistry—Polymers—Metallurgy—Inorganic Materials—Reactor

Radiation—Physical Chemistry.

THE INSTITUTE FOR APPLIED TECHNOLOGY provides technical services to pro- mote the use of available technology and to facilitate technological innovation in industry and Government: cooperates with public and private organizations leading to the development of technological standards (including mandatory safety standards'), codes

and methods of test; and provides technical advice and services to Government agencies

upon request. The Institute also monitors NBS engineering standards activities and

provides liaison between NBS and national and international engineering standards

bodies. The Institute consists of the following technical divisions and offices: Engineering Standards Services—Weights and Measures—Flammable Fabrics

Invention and Innovation—Vehicle Systems Research—Product Evaluation

Technology—Building Research—Electronic Technology—Technical Analysis

Measurement Engineering.

THE CENTER FOR COMPUTER SCIENCES AND TECHNOLOGY conducts re- search and provides technical services designed to aid Government agencies in improving cost effectiveness in the conduct of their programs through the selection, acquisition,

and effective utilization of automatic data processing equipment; and serves as the principal focus within the executive branch for the development of Federal standards for automatic data processing equipment, techniques, and computer languages. The Center

consists of the following offices and divisions: Information Processing Standards—Computer Information—Computer Services —Systems Development—Information Processing Technology.

THE OFFICE FOR INFORMATION PROGRAMS promotes optimum dissemination

and accessibility of scientific information generated within NBS and other agencies of

the Federal Government; promotes the development of the National Standard Reference Data System and a system of information analysis centers dealing with the broader

aspects of the National Measurement System; provides appropriate services to ensure

that the NBS staff has optimum accessibility to the scientific information of the world,

and directs the public information activities of the Bureau. The Office consists of the following organizational units: Office of Standard Reference Data—Office of Technical Information and

Publications—Library—Office of Public Information—Office of International

Relations.

1 Headquarters and Laboratories at Gaithersburg, Maryland, unless otherwise noted: mailing address Washington. D C. 20234.

- Part of the Center for Radiation Research.

a Located at Boulder. Colorado 80302.
NATIONAL BUREAU OF STANDARDS REPORT

NBS PROJECT NBS REPORT

4047211 March 17, 1969 10 010

EXAMINATION OF

MILEAGE MEASURING DEVICES

(Prelim inary Report of a Manual for Weights and

Measures Officials)

by

S. H asko and C . H . Schreyer

IMPORTANT NOTICE NATIONAL BUREAU OF <

for use within the Government

and review. For this reason, whole or in part, is not autt Bureau of Standards, Washinj

the Report has been specitical

Approved for public release by the

Director of the National Institute of

Standards and Technology (NIST)

on October 9, 2015.

ress accounting documents intended

is subjected to additional evaluation

re listing of this Report, either in he Office of the Director, National

by the Government agency for which

copies for its own use. <NBS>

U.S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

CONTENTS

Page

Procedure for the Calibration of Fifth Wheel

Testing Equipment 1

1 . Introduction 1 2. Calibration of Fifth Wheel 1 2. 1. Layout of Measured Course 3

2.2. Fifth Wheel Calibration Procedure 9

Procedure for the Examination and Test of Rental Car

Odometers Using Fifth Wheel Testing Equipment 20

1. Introduction 2 0

2. Selection of Test Site 20

3. Test Preparation 24

4. The Test 26

5. Test Report Form 30

6. Reporting a Test 30

6.1. Test Data 30

6.2. Test Calculations 30

Appendix 35
ILLUSTRATIONS

Figure 1

Figure 2

Figure 3

F igure 4

Figure 5.

Figure 6.

Figure 7.

Figure 8.

Figure 9.

Figure 10.

Figure 11.

Figure 12.

Figure 1 3.

Figure 14.

Figure 1 5.

Figure 16.

A schematic drawing of a typical fifth wheel assembly.

Laying out a measured course.

Fifth wheel in calibration position on measured course.

Determination of signs (plus + or minus -) and the limitations of alignment for start and finish of fifth wheel

calibrations.

A suggested fifth wheel calibration report form.

Measuring distance from fifth wheel to starting point of

measured course.

Synchronizing electrical contactor of fifth wheel with

starting point of test.

A completed fifth wheel calibration report form.

Typical speedometer-odometer assembly of a motor vehicle.

A special cable-driven odometer.

A hub odometer.

A suitable test site.

Fifth wheel in test position on test vehicle.

Alignment of numbers of tenth mile indicator.

Suggested Test Report Form.

A completed Test Report Form.

ii
PROCEDURE

for the

CALIBRATION OF FIFTH WHEEL TESTING EQUIPMENT

1. Introduction

The fifth wheel is a commercially available mileage-measuring

device recommended for use by weights and measures officials as a

portable standard test instrument for testing the accuracy of odometers

on rented highway vehicles. The fifth wheel may also be used for testing taximeters. Information on the design of a fifth wheel device, including illustrations and general specifications, may be found in National

Bureau of Standards Technical Note 195, titled "Report on Technical

Investigation of Odometers." Copies of this report may be obtained

from the NBS Office of Weights and Measures. For the convenience of

the reader, a schematic drawing of the fifth wheel assembly is shown

in Figure 1. Specifications for additional test equipment as used in

these procedures are given in the appendix.

2. Calibration of Fifth Wheel

A fifth wheel must be calibrated on a carefully selected and accurately measured road course. A concrete or "black-top" asphalt

roadway having no loose stones or gravel is preferred over macadam

because of marking or tacking required during measurement. The site

should consist of 1 1 /4 to 1 1/2 miles of flat, straight road with little
ELECTRICAL

COUNTER ELECTRICAL PNEUMATIC TIRE

Figure 1

A schematic drawing of a typical fifth wheel assembly.
traffic. A four-lane or divided road is preferred. If a flat and straight

road cannot be found, one with a gentle hill may be tolerated, but hazards to personnel and traffic should be minimized. The crown of the

road should not exceed 2 percent (i. e. , 0. 02-foot rise per foot of width).

2. 1. Layout of Measured Course

The laying out of a one-mile course can be completed in one day

using three or four men. One man is needed to hold the tape at the initial mark, a second to hold the tape under tension while measuring and

to keep a record of the measurements, and a third man to mark or tack

the 100-foot intervals as measured (See Fig. 2. ). The fourth man would

act as a flagman and could move the vehicle, which should be equipped

with "4-way" blinking caution lights, or other safety lights. The following equipment will be needed to lay out the course:

(a) A 100-foot steel surveyor's tape standard (certified by

appropriate authority).

(b) A calibrated six-inch steel rule (optional).

(c) A calibrated straight-face spring scale of at least 10

pounds capacity.

(d) Masonry nails and fiber-tip marking pen, or surveyor's tacks.

(e) Hammer.

(f) Paint (aerosol spray type).

(g) Thermometer (complete immersion type), 1-degree

graduations.

3
Figure 2. Laying out a measured course.

4
Safety should be the primary consideration in the selection of

the starting position. Clear visibility of at least one-quarter mile

will give oncoming vehicles adequate stopping distance if needed.

Step (1): Mark starting point permanently with a case-hardened masonry

nail embedded in the road surface two feet from the edge of the

roadway. Spray paint a circle around the marker and a perpendicular line from the marker to the road edge.

Step (2): Record air temperature.

Step (3): Initiate measurement of one-mile test course. Place 100-

foot mark of steel tape in line with the exact center of starting marker and lay out tape on road surface two feet in from

and parallel to the edge of the road and hold under ten pounds

tension as determined with a straight-face spring scale.

Mark or tack roadway surface at the zero mark on the tape.

Scribe the marker or tack with the exact measurement line.

Spot the mark or tack with a circle of paint, to facilitate relocating it.

Step (4): Continue this measuring procedure in a straight line parallel

with, and two feet in from edge of roadway until exactly one

mile is measured with the tape. Note that one mile is 52

lengths of the 100-foot tape plus 80 feet.

5
CAUTION: Do not drag the tape on the road surface

between measurements. The tape must

be lifted clear of the ground each time it

is moved to a new position.

Step (5): Record air temperature.

Step (6): Move exactly two feet down the road beyond the one-mile mark,

and establish a new temporary starting point.

Step (7): Repeat the measuring procedure in the reverse direction along

the same route. The finish point should be within two feet short

(plus or minus five inches 1) of the permanently marked starting point. If this agreement is lacking, the measurement procedure should be thoroughly reviewed for sources of error and

the entire measurement procedure repeated. It is important

that* the change in average temperature between each one -mile

measurement does not exceed 2° F. or the temperature correction factor for steel tapes must be considered. Temperature

correction is discussed in the next step, but it should be noted

now that there may be a change in the length of a measured

1 This is a tentative tolerance figure based on experience of personnel

with some preliminary training. Exceedance of this tolerance usually

indicates either (1) presence of gross errors in one or both measurements, or (2) improper tape handling.

6
mile of 12/32 inches for each degree change in average temperature. The true one-mile point will be determined after

making corrections for temperature and error in the tape.

Step (8): Correct for temperature. Since steel tapes are calibrated at

68° F. , a correction must be made for the length of the tape

at the temperature of use. The change in length amounts to

. 00774 inch per degree F. on a 100-foot steel tape. This can

be converted with sufficient accuracy to 13/32 inch per degree

temperature difference for each measured mile. The total

change in tape length is 13/32 inch multiplied by the difference

between the average temperature and 68° F. multiplied by the

measured miles.

The formula derived is:

13/32 x TD x M = TC -- Where TD = temperature difference (°F

M = length of course (miles)

TC = temperature correction (in

For example, say the starting temperature were 80°, the

temperature at the conclusion of the measuring were 82°, and

the measured course were 1 mile.

Applying these figures to the formula, the computation would be:

13/32 x (81 - 68) x 1 =

13/32 x 13 x 1 = 5 5/16 inches

7
As the average temperature is warmer than 68° F. the tape

would be longer in use; thus the 5 5/16 inches must be subtracted. Conversely, if the average temperature were colder

than 68° F. the tape would contract and the answer obtained

would be added. [Specifically, if the average temperature is

more than 68° F. subtract the computed temperature correction,

and if the average temperature is less than 68° F. add the

computed temperature correction. ]

Step (9): Correct for error in the tape as certified. To illustrate, the

tape was found to be 100. 003 feet long at 68° F. under a tension

of 10 pounds. Thus, the tape has an error of +. 003 feet. In

laying out a one-mile (5, 280-ft) course, the 100-foot tape was

used 52. 8 times. With an error of +. 003, the tape error would

be computed as +. 003 ft x 52. 8 = . 1584 ft. In converting to

inches, . 1584 ft x 12 = 1. 9 inches, or 1 7/8 inches. As the

tape is actually longer than 100 feet, the 17/8 inches must be

subtracted.

Step (10): Summarize corrections. The original or corrected original

measured course would then have a final correction as follows:

Temperature correction -5 5/16

Tape error -1 14/16

Total correction to be applied -7 3/16

8
Step (11): Embed another masonry nail marker permanently into the

roadway 7 3/16 inches closer to the starting point from the

end mark of the first mile measurement. This true or correct one-mile marker is spotted with paint similar to the

way the starting point was marked by spray painting a circle around the marker and then a perpendicular line from

the circle to the road edge. The permanently embedded

markers indicate the starting and finishing points of an accurately measured one-mile course. Erect start and finish

identification signs at the proper markers.

2.2. Fifth Wheel Calibration Procedure

The fifth wheel in its test position may be difficult to see by a following motorist. If not supplied by the manufacturer, a warning flag

should be made and attached to the frame of the device np*xt to or over

the wheel in such a manner that it is at eye-level to the driver of a following vehicle (See Fig. 3. ). In addition, the four-way hazard warning

signals of the test vehicle should be operating whenever a test is being

conducted.

If the electrical counting head of the fifth wheel is to be powered

from the cigaret lighter socket, a connecting wire at least 15 feet in

length should be provided. This length is recommended to permit placing the counter close to the fifth wheel when adjusting for zero start

position.

Step (1): Attach the fifth wheel to the rear bumper of a motor vehicle

9
Figure 3. Fifth wheel in calibration position on measured course.

10
with the bumper clamp (and any auxiliary clamps --if needed).

Do not install the fifth wheel in a position where the exhaust

gases of the vehicle blow directly on any part of the fifth wheel

or its components (clamps, frame, rim, tire of the electrical

contactor). Make all necessary connections between the fifth

wheel and the counting mechanism which should be placed on

the front seat of the vehicle.

Step (2): With the fifth wheel in operating position, and at a tire pressure

of 26 to 28 psi, drive for at least five miles to develop a stabilized tire pressure. At the measured course drive slowly past

the starting marker until the fifth wheel is aligned as closely

as possible with the marker (Fig. 3. ). The point of contact of

the fifth wheel with the road should be less than 10 inches from

the starting line. (See Fig. 4. ) Stop and set parking brake.

Step (3); Adjust fifth wheel tire pressure to exactly 25 psi.

Step (4): Measure the distance the fifth wheel is from the starting point

and record. (See Item 1, Fig. 5. , Report Form. ) The use of

a plumb bob (Fig. 6. ) from the center point of the fifth wheel

axle to the road surface will aid in measuring this distance.

Give proper sign to value (plus or minus) as indicated in

Figure 4. This measurement is zero if the fifth wheel is

exactly aligned with the starting point.

11
+ - +

X-LESS THAN 10 INCHES

Y-LESS THAN 75 INCHES

Figure 4. Determination of signs (plus + or minus -) and the limitations

of alignment for start and finish of fifth wheel calibrations.

12
(Department Heading) Date

Calibration Test Report of Fifth Wheel

Make of Fifth Wheel Serial No. Tire Pressure (Fifth Wheel) psi. Length of Course Where Tested Avg. Temp. Weather ~

Run Numbers

Test Data

1 2 3 4 5 Avg.

1. Distance (inches) of fifth wheel from START marker

(Before marker is PLUS value; after marker is MINUS value*)

2. Distance (inches) of fifth wheel beyond FINISH markej

(This is always a PLUS value*)

3. Total distance from markers (Item 1 plus Item 2)

4. Reading on Counter (in thousandths of a mile)

5. Corrected reading [Item 4 minus 0. 001 mile if total distance

(Item 3) equals or exceeds 31 11/16 inches]

^'Distances should be indicated as plus, minus, or zero as indicated here: Before After Beyond

+

+

° 1 Measured Course

Start Finish

6. Over a measured course of miles. The calibration test indicates that the Fifth Wheel measures miles (Item 5, Average).

7. Calibration correction (Item 6, minus Item 5, Average) and

retain (+) or (-) sign.

If Item 6 is larger than Item 5, Average, the calibration correction is plus (+). If Item 5, Average, is larger than Item 6, the correction is minus (-).

Inspector Title

Figure 5. A suggested fifth wheel calibration report form.

13
Figure 6. Measuring distance from fifth wheel

to starting point of measured course.

14
Step (5): With the counter located in a viewable and audible position.

lift the frame of the fifth wheel and freely rotate the tire in

a forward direction for several clicks in the counter. This

will remove any backlash in the gears. With the wheel turning very slowly stop the rotation the instant a full number

clicks into place on the counter (Fig. 7. ) and lower the

frame until the tire is in firm contact with the road surface.

The wheel contactor is now synchronized with the starting

point for the test. Place the counter in the vehicle in view

of the driver and clear to zero.

Step (6): Accelerate without spinning wheels to 35 mph, and maintain

this speed as constant as possible throughout the calibration

run. Maintain a uniform distance between the vehicle and the

road edge during the calibration run.

Step (7): As the final marker is approached, decelerate to a slow speed.

Stop the vehicle the instant the counter registers the first

whole number after the fifth wheel has passed beyond the final

marker. Record on the Report Form, under Item 4, the

counter indication.

Step (8): Measure the distance the fifth wheel has passed beyond the final

marker (same method as Step 4) and record on Report Form,

15
Figure 7. Synchronizing electrical contactor of

fifth wheel with starting point of test.

16
under Item 2. This distance should be less than 75 inches

Step (9):

Step (10):

Step (11):

Step (12);

Step (13):

and is always a plus value.

Complete Report Form for Run 1.

Continue making test runs until three complete runs are made

with not more than 16 inches difference between the total distances of individual runs. See completed Report Form.

Fig. 8. Some difficulty may be experienced in meeting this

requirement if the atmospheric temperature change exceeds

4°F. per hour.

If the sum of total distances from the starting and finishing

marks (Item 3, Report Form) equals or exceeds 31 11/16 inches,

subtract 0. 001 mile from the counter reading (Item 4, Report

Form) to obtain the corrected counter reading (Item 5, Report

Form). If Item 3 is less than 31 11/16 inches, the corrected

counter reading is the same as Item 4 (the original counter

reading).

Obtain average corrected counter reading (Item 5, Average).

This indicates the mileage measured by the fifth wheel over

the measured course.

Complete the Report Form. As indicated on the Report Form

the calibration correction is obtained by subtracting the

17
average corrected distance recorded by the fifth wheel (Item

5, Average) from the length of the measured course and retaining the proper + or - sign. If Item 6 is larger than Item

5 the calibration correction is plus (+). Conversely, if Item

5 is larger than Item 6 the correction is minus (-).

The fifth wheel appears to be slightly temperature sensitive. Changes of as much as 0. 001 mile per mile per 20° F.

change in calibration temperature have been noted. Thus,

calibrations should be made at approximately 30° F. intervals

in the temperature range of intended use. The temperature

range of intended use should not be more than 20° F. from a

calibration temperature. Keep copies of all calibrations with

the fifth wheel when testing odometers and taximeters.

18
(Department Heading) 3—; Calibration Test Report of Fifth Wheel a e—

~2~lh L i Make of Fifth Wheel <. k ]>>.; f

Serial No. 0 V Tire Pressure (Fifth Wheel) 2 n psi. Length of Course / /.V Where Tested C,. ,-j, PM . Avg. Temp. Weather ,y

Test Data Run Numbers

i 2 3 4 5 Avg.

1. Distance (inches) of fifth wheel from START marker

(Before marker is PLUS value; after marker is MINUS value*)

2. Distance (inches) of fifth wheel beyond FINISH marker

(This is always a PLUS value*)

3. Total distance from markers (Item 1 plus Item 2)

4. Reading on counter (in thousandths of a mile)

5. Corrected reading [Item 4 minus 0. 001 mile if total distance

(Item 3) equals or exceeds 31 11/16 inches]

in

i- V7

/ Cc'<>

- ;2,

TVS’

* *11-

1 C< (>

f- s r^7

/.CC'i'

O^nn c.nnn C

ct<in

*Distances should be indicated as plus, minus, or zero as indicated here: Before After Beyond

+

Start Measured CourseFinish

6. Over a measured course of The calibration test indicates that the Fifth Wheel measures

7. Calibration correction (Item 6, minus Item 5, Average

and retain (+) or (-) sign.

If Item 6 is larger than Item 5, Average, the calibration correction is plus (+). If Item 5, Average, is larger than Item 6, the correction is minus (-).

/ o c c- (> nnn

rn. act

miles. miles (Item 5, Average).

*uL

Figure 8. A completed fifth wheel calibration report, form.
PROCEDURE

for the

EXAMINATION AND TEST OF RENTAL CAR ODOMETERS

USING FIFTH WHEEL TESTING EQUIPMENT

1. Introduction

An automobile odometer is a mileage measuring device indicating in units of miles and tenths of miles. The primary indicating element of an odometer may be (a) the mileage traveled portion of the

"speedometer" assembly of a motor vehicle (Fig. 9. ), (b) a special

cable driven mileage-indicating device (Fig. 10. ), or (c) a hub odometer

attached to the hub of a wheel on a motor vehicle (Fig. 11. ). When the

vehicle is in motion the most sensitive indicating element of an odometer;

namely, the tenth mile indicator (analog) should advance continuously.

The test of an odometer may be conducted as a road test, a fifth

wheel test, or both. A road test consists of driving the vehicle over an

accurately measured road course. A fifth wheel test consists of driving

the vehicle over a road course and determining the distance actually

traveled through the use of a mileage measuring device, (fifth wheel)

attached to the vehicle and that independently measures and indicates the

distance. This procedure is concerned with the latter test method.

2. Selection of Test Site

The odometer code in NBS Handbook 44 specifies a test of two

miles at an approximate speed of 45 miles per hour. Thus, the test route

20 -
ODOMETER

WINDOW

io

MILE

INDICATOR

SPEEDOMETER

ODOMETER

MILE

INDICATOR

Figure 9. Typical speedometer-odometer assembly of a motor vehicle

21
ODOMETER WINDOW

Figure 10. A special cable-driven odometer.

22
ODOMETER

MOUNTING HOLES

AND BOLTS

^r^g-Qj'0 11. A hub odometer.

23
(Fig. 12. ), (a) should be at least 2 1/2 miles long (to provide a half

mile starting zone), (b) have a speed limit of at least 45 miles per

hour, and (c) be free of traffic interference and traffic control devices.

In addition, a paved shoulder or parking lane should be available where

the test vehicle and attached fifth wheel may be temporarily parked before the test run is started and again at the conclusion of the test run,

and the road crown should not exceed two percent. Every consideration

should be given to a test site having good visibility. To save time the

test site should be usable in both directions.

3. Test Preparation

Step (1): Inspect the vehicle under test. For a discussion of the purposes and scope of the "inspection" as distinguished from

"testing" see Section 4, NBS Handbook 44, "Specifications,

Tolerances, and Other Technical Requirements for Commercial Weighing and Measuring Devices."

Step (2): Record the following information: Date, test number, vehicle

owner, address, make, year, model, body style, serial

number, license number, and identification number of vehicle

under test. Also record the make, style, ply, and size of the

rear tires. Note the temperature and road condition.

Step (3): Attach the fifth wheel to the rear bumper of the test vehicle

24
NO STOP SIGNS OR TRAFFIC LIGHTS.

REASONABLY STRAIGHT WITH NO SHARP TURNS.

GOOD VISIBILITY.

THE PARKING LANE OR PAVED SHOULDER IS A

NECESSITY IN THE STARTING ZONE.

Figure 12 A suitable test site
(See Fig. 13. ) with the bumper clamp (and any auxiliary

clamps- -if needed). Do not install the fifth wheel in a position

where the exhaust gases of the test vehicle blow directly on any

part of the fifth wheel or its components (clamp, frame, rim,

tire, or the electrical contactor). Make all necessary connections between the fifth wheel and the counting mechanism which

should be placed on the front seat along side the inspector.

Test conditions specify that the vehicle shall carry two persons.

If the inspector is to examine the vehicle alone, he should have

available three 50-pound test weights to be placed on the floor

in front of the front seat opposite the driver.

Step (4): Inflate the rear tires of vehicle to 30 psi and the fifth wheel

tire to 2 8 psi. Stabilize test vehicle and fifth wheel tires with

a run of at least five miles. This may be accomplished on the

way to the test course.

4. The Test

The four-way hazard warning signals of the vehicle under test

should be operating whenever a test is being conducted.

Step (1): Drive slowly in the starting zone of the test course until the

horizontal bar of the numeral 2, 4, 5, or 7 of the one-tenth

mile indicator is lined up with the top or bottom of the odometer

window and stop. The precision or repeatability of the test

runs is dependent on how well the odometer is read. The

position of the selected numeral of the one-tenth mile indicator

26
Win**

Figure 13. Fifth wheel in test position on test vehicle.

27
(See Fig. 14. ) can be most easily reproduced if aligned

Step (2):

Step (3):

Step (4):

Step (5):

Step (6):

Step (7):

Step (8):

closely to the upper or lower edge of the window of the

odometer. The inspector should hold his head and eyes in

the same position relative to the odometer to eliminate the

possibility of error due to parallax.

Drive the vehicle very slowly until a full number "clicks" into

position on the fifth wheel counter and stop. The added distance

required to obtain a full number "click" on the fifth wheel counter

should not affect the alignment of the numeral on the tenth-mile

indicator.

Record odometer reading and reset counter to zero.

Adjust rear tires of test vehicle to 28 psi and fifth wheel tire

pressure to 25 psi.

Accelerate to 45 mph without spinning wheels. Maintain speed

until ready to decelerate, without skidding, to complete twomile run on odometer. The one-tenth mile indicator should be

at exactly the same position as at the start of the test.

Record odometer reading.

Record fifth wheel counter reading. If counter is not at a full

number "click," record the highest full number in view.

Recheck vehicle tire pressure.

28
TOP BOTTOM

EDGE OF

ODOMETER WINDOW

Figure 14. Alignment of numbers of tenth mile indicator.

29
Step (9): Repeat test run (steps 1 through 8) in opposite direction.

5. Test Report Form

A suggested Test Report Form is shown in Figure 15. The form

provides space in sections A and B for the necessary owner, vehicle,

and tire identification. Section C of the form provides space for recording the test data for as many as three separate test runs and for the calculations involved. Sections D and E provide space for indicating the

official action taken as a result of the test, any remarks or instructions,

the signature of the inspector, and the "acknowledgment" signature of the

vehicle owner or operator. Sections A and B of the Report Form should

be filled in completely prior to operation of the vehicle for test purposes.

A separate form (or more than one form if more than three runs are

made) should be used for each vehicle tested.

6. Reporting a Test

6. 1. Test Data

The test data is entered at the appropriate spaces on the Report

Form during and immediately following the test runs.

6.2. Test Calculations

In Figure 16 a sample Report Form has been filled out. In the test

data section of the form, each line for each run is identified by a number.

30
Department Heading

Odometer Test Report Form

DATE TEST NO.

A. Vehicle Identification:

Owner Address Make of Car Year- and Model Body Style

License No. Serial No. Co. Ident. No.

B. Description of Rear Tires:

Make Style Ply Size

Tire Pressure: After Stabilization After 1st Run

After 2nd Run After 3rd Run

C. Test Data:

Temperature Road Conditions

1st Run 2nd Run 3rd Run

1. Odometer end of test

2. Odometer start of test

3. Odometer mileage

(Item 1-Item 2)

4. Test Instrument Reading _____

5. Calibration correction x 2 6. True mileage

(Item 4+Item 5) 7. Error (see note)

8 . Percent error

( Item 7 x 100)

(Item 6 )

NOTE: If true mileage reading (Item 6) is smaller than the odcmeter reading

(Item 3), the vehicle is overregistering and a minus sign should be

used for the error. If the mileage reading is larger than the odometer

reading, the vehicle is underregistering and a plus sign should be used

for the error value.

D. Action Taken: Approved Rejected Condemned

E . Remarks :

Inspector Owner/Operator

Figure 15. Suggested test report form.

31
Department Heading

Odcmeter Test Report Form

DATE 7. IS-L.9 TEST NO.

Vehicle Identification:

^

Address iZia lOU* /riae/Ja ajl erUJ^£A«1-- m Address /5/4 — Make of Car fn^ -i-r-n Year and Model Style _ License No. Serial No. Co. Ident. No. 3

B. Description of Rear Tires:

M^e Q> £>cde.nu Style Ply & Size £ , - / V Tire Pressure: ter Stabilization After 1st Run £ g jO.c;

After 2nd Run_ After 3rd Run

C . Test Data

Temperature_ _Road Conditions_

1st Run 2nd Run 3rd Run

1. Odometer end of test

2. Odometer start of test

3 . Odometer mileage

(Item 1-Item 2)

4. Test Instrument Reading

5. Calibration correction x 2

6 . True mileage

(Item 4+ Item 5)

7. Error (see note)

8 . Percent error

( Item 7 x 100)

(Item 6 )

03AiL7

<SL£.

t Qt Q.Q2r> —a m

^ 6, Oq4

- QxSLd

2L-0

_LM£_

t C 1 6QjLf

L g?-7- - 0,0^3 — /!!?

NOTE: If true mileage reading (Item 6) is smaller than the odometer reading

( Item 3 ) , the vehicle is overregistering and a minus sign should be

used for the error. If the mileage reading is larger than the odcmeter

reading, the vehicle is underregistering and a plus sign should be used

for the error value.

D. Action Taken: Approved_ _Rej ected_ Condemned

E . Remarks : i±L tires

Owner/ Operator

Figure 16. A completed test report form.

32
The several steps and appropriate entries in the data calculations in

these runs will refer to the identifying numbers for the appropriate

runs.

Step (1): The odometer mileage (Item 3) is the odometer reading at the

end of the test (Item 1) minus the odometer reading at the

start of the test (Item 2).

Step (2); The test instrument reading (Item 4) is the reading of the fifth

wheel at the end of a run.

Step (3): The calibration correction x 2 (Item 5) is the fifth wheel calibration correction which is generally expressed in plus (+) or

minus (-) thousandths of a mile per mile and is multiplied by 2

since the test runs are two miles in length.

Step (4): The true mileage (Item 6) is the sum of Item 4 and Item 5.

Step (5): The error (Item 7) is the true mileage (Item 6) minus the

odometer mileage (Item 3). The proper plus (+) or minus (-)

sign should be carried; thus, if the true mileage reading

(Item 6) is smaller than the odometer reading (Item 3) the

vehicle is over-registering and a minus sign should be used for

the error. If the mileage reading is larger than the odometer

reading the vehicle is under-registering and a plus sign should

be used for the error.

33
Step (6): The percent (%) error (Item 8) is determined by dividing the

error (Item 7) by the true mileage (Item 6) and multiplying

by 100. Be sure to carry the appropriate plus (+) or minus

(-) sign.

34
APPENDIX

Additional Test Equipment.

Additional test equipment used in these procedures.

Thermometers--Liquid-in-glass, total immersion type,

-30 to 120°F. , at least 1°F. graduations, at least

12 inches in length.

Master Gage- -Calibrated 1 to 130 lbs in 1-lb units,

2 1 /2-inch gage dial, dual chuck, pressure retaining valve, pressure release, plush-lined case.

Pencil Tire Gages --Calibrated 8 to 40 lbs in 1-lb units.

Steel Surveyor's Tape--100-ft standard, certified by prope

authority.

Hand Spring Scale--Calibrated straight face, at least

10 pounds capacity, for measuring tension on steel

tape.

Calibration of Pencil Tire Gages.

The pencil tire gages may be calibrated with the master gage

in the following manner:

1) Inflate a vehicle tire to approximately one psi over the

recommended test tire pressure.

2) Take tire pressure reading with master gage.

3) Take two tire pressure readings with the pencil tire gage

and determine average.

35 -
4) Take another tire pressure reading with master gage.

5) Determine average of the two master gage readings, i. e. ,

Item 2 and Item 4.

6) Difference between Item 5 and Item 3 is the pencil tire

gage correction. (NOTE: Be sure to retain proper + or

- sign.

)

e. g. , Correction = Item 5 - Item 3

or if Item 5=25 psi

and Item 3 =26 psi

Correction = 25 - 26 = -1 psi

7)

Repeat Steps 1 through 6 at least two more times to be

sure that the correction is reproducible. Discard

pencil tire gage if correction is not reproducible.

36 -

I II