NBSIR 75-755

The CPSC Road Test of Bicycle

Braking Performance - Experimental Evaluation

Donald E. Marlowe

Engineering Mechanics Section

Mechanics Division

Institute for Basic Standards

National Bureau of Standards

Washington, D. C. 20234

August 1 975

Final

Prepared for Office of Consumer Product Safety

Center for Consumer Product Technology

Institute for Applied Technology

National Bureau of Standards

Washington, D. C. 20234

NBSIR 75-755

THE CPSC ROAD TEST OF BICYCLE

BRAKING PERFORMANCE - EXPERIMENTAL EVALUATION

Donald E. Marlowe

Engineering Mechanics Section

Mechanics Division

Institute for Basic Standards

National Bureau of Standards

Washington, D. C. 20234

August 1975

Prepared for Office of Consunner Product Safety

Center for Consumer Product Technology

Institute for Applied Technology

National Bureau of Standards

Washington, D. C. 20234

U.S. DEPARTMENT OF COMMERCE, Rogers C.B. Morton, Secretary

James A. Baker, III, Under Secretary

Dr. Betsy Ancker-Johnson, Assistant Secretary for Science and Technology

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Acting Director

Final

CONTENTS

Page

1. SCOPE 1

1.1 Test Purpose 2

1.2 Test Equipment 2

1.3 Test Flow 2

2. APPARATUS 2

2.1 Handbrake Lever Loading Fixture 2

2.2 Ground Marker System 2

2 . 3 Timer 3

3. TEST CONDITIONS 3

3.1 Test Surface 3

3.2 Rider 3

4. PROCEDURE 4

4.1 Set-up for Primary Handbrake Lever 4

4.2 Set Up for Extension Hand Brake Lever 5

4.3 Set Up for Coaster Brake Systems 5

4.4 Testing 6

4.4.1 Handbrake Loading Test 6

4.4.2 Rocking Test

4.4.3 Performance Test 6

5. TEST RESULTS 7

6. DISCUSSION 7

6.1 Loading and Rocking Test 7 6.2 Braking Test 7 6.3 Coefficient of Friction and Effect of Pavement Surface 8

6.4 Rider Reaction Times 8

6.5 Effect of Rider Weight 9

7. CONCLUSIONS 9

8. REFERENCES 10
LIST OF FIGURES

Figure 1 - Flow Diagram for Handbrake Tests

Figure 2 - Handbrake Loading Fixture

Figure 3 - Loading Apparatus on a Bicycle

Figure 4 - Ground Marker System

Figure 5 - Velocity-Timer Apparatus

T?-! on A

Figure 7 - Firing Switch for Coaster Brakes

Figure 8 - Braking Test Data Sheet

Figure 9 - Bicycle Performance Test Sample Calculation
THE CPSC ROAD TEST OF

BICYCLE BRAKING PERFORMANCE - EXPERIMENTAL EVALUATION

Donald E. Marlowe

ABSTRACT

The brake performance criteria to be published

as part of a mandatory regulation on bicycle safety

requirements has been evaluated. Fifteen bicycles

were tested in accordance with the regulation.

A mathematical adjustment of the actual test speed

of the bicycle to 24 km/hr (15 mph) is necessary

before the weight allowance can be made to the

stopping distance in the evaluation of these tests.

A danger of injury to the test rider exists during

the tests and future efforts should be made toward

replacement of these tests with a simpler laboratory

procedure

.

Key Words: Bicycles; braking; consumer safety;

handbrake; safety; testing.

1 . SCOPE

Accident reports received by the Consumer Product Safety Commission

list many injuries to children as a result of accidents involving bicycles.

Many of these injuries result from the inability of the bicycle to stop

quickly in an emergency situation. As a result, the Commission has included a series of handbrake performance criteria in the mandatory re- gulation on bicycle safety requirements which they have prepared.

1.1 Test Purpose

This report describes tests which were performed at the National

Bureau of Standards as a partial evaluation of the braking tests called

for in the Federal Bicycle Safety Regulation, Requirements for Bicycles,

July 16, 1974 [l]. These tests included the Loading Test (1512.18(d)(2 )(i ))

the Rocking Test (151 2 . 1 8 (d )( 2 ) ( iii ) ) and the Performance Test (1512.18

(d)(2)(v)).

"The numbers in parentheses refer to paragraphs of the proposed

regulation.
1.2 Test Equipment

The test equipment assembled for these tests included a force gage,

handbrake loading assembly, an electronic timer for measurement of bicycle

velocity, a ground position marker gun assembly and a level paved surface

upon which to perform the tests.

1.3 Test Flow

The flow of procedures followed in these tests is shown in Figure 1.

' 2. APPARATUS

2.1 Handbrake Lever Loading Fixture

A loading fixture (Figure 2) which incorporates a 445 N (100 Ibf)

spring force gage and a gripping linkage for attachment to the brake

lever was fabricated for these tests. This apparatus was based on a design

which had been developed at the University of Iowa. In use, the apparatus

is mounted on the handlebar (Figure 3) and grips the brake lever. The

rider applies force to the apparatus lever. This lever pushes up on the

force gage which is connected through the linkage shown to the brake

lever. An engineering drawing of this apparatus is provided in the Appendix.

At the instant the rider begins to apply force to the lever, a switch

on the force gage is closed and the ground marker system is actuated.

A second switch could be actuated at a predetermined force level.

2.2 Ground Marker System

The marker system is used to indicate on the ground the point at

which the brakes were first applied. For these tests, a marker gun designed for use as an automobile driver education aid was modified for

mounting on a bicycle. The system (Figure 4) included the double barreled

gun, a twelve volt battery, the switches mounted on the loading assembly,

the marker cartridges which are supplied with the gun, and the wiring

necessary to connect the switch, gun, and battery in series. The marker

cartridges contained a yellow, quick drying paint. During the tests

reported here, for the bicycles equipped with handbrakes, a first cartridge was fired at the instant brakes were applied and a second at the

instant the applied force equaled 178 N (40 Ibf). The distance between

the two marks so produced was used to estimate the rider's actuation

time for the system. In addition, several tests were conducted with

a second, nominally identical gun system mounted on the bicycle. This

system was wired to the opposite side loading assembly and could be

used to estimate the left-hand-right-hand coordination of the brake

levers.

2
For the tests on bicycles equipped with a coaster brake, the marker

system was actuated by the backward motion of the drive chain as the

brake was applied (Figure 7).

The batteries used to actuate the solenoid in this system posed

a special problem. In the use for which the solenoid fired gun was designed, the power from an automobile battery is used, and is continuously

recharged. In this application, the first tests were made using two,

6 volt lantern batteries connected in series. These quickly discharged

to a point where they would no longer actuate the solenoid and had to

be replaced. This often occurred before testing could be completed on one bicycle. To eliminate this problem, a rechargeable 12 volt battery

used to start a walk behind lawn mower was chosen. The battery had enough

capacity to allow the testing of up to 3 bicycles before it needed recharging,

2.3 Timer

An electronic timer, capable of measuring the elapsed time between

two similar events to within one microsecond, was used to record the

time interval between passage of the bicycle wheels over a tape switch

on the ground. Knowing the elapsed time and the wheel base of the bicycle,

the velocity of the bicycle could be calculated. The equipment used

is shown in Figure 5. It shows the timer, a 1.5 m (5 ft) long ground

tape switch, and a battery to power the switch circuit.

3. TEST CONDITIONS

3.1 Test Surface

The test surface required for these tests is a dry, clean, level,

paved surface of a length adequate to accommodate the bicycle during

the performance test. For these tests, an outdoor asphalt parking lot

approximately 90 m (300 ft) long was used. The measured slope of this

surface was 0.3 percent. To compensate for the effects which this slope

and prevailing winds might have on the average stopping distance, alternate

braking tests were made in opposite directions across the timing strip.

Before any tests were conducted, any moisture which might have accumulated

on the surface during the previous night was allowed to dry. The co- efficient of static friction was measured between this surface and the

tire of one bicycle included in this program. This will be discussed

in section 6.3.

3.2 Rider

As has been realized from the beginning of these tests, the largest

variable is probably the test rider. While the tangible effects of his

weight on stopping distance can be allowed for, other rider related

effects such as reaction time, agility, anticipation and confidence

3
have not been well quantified. Several measurements were made during

these tests in an effort to define reaction time and agility (the ability

to coordinate left-hand-right-hand brake actuation). The problem of

rider confidence, or lack of it, has so far defied numerical measurement.

Five riders have tested bicycles for this program. Several bicycles

were tested by more than one rider. A discussion of these tests will

be given later. It should be noted here, however, that every rider crashed

at least one bicycle. For this reason, all test riders should be equipped with suitable safety equipment, including a helmet, to minimize

the injuries possible during an accident.

4. PROCEDURE

The following is a detailed description of the procedure followed

during testing in accordance with paragraph 1512.18 (d) of the proposed

regulation:

1) Assemble the bicycle according to the instructions provided by the

manufacturer.

2) Inflate the tires to the pressure molded into the tire sidewall.

Record the tire pressure.

3) The test rider should ride the bicycle to familiarize himself with

its behavior in the various gear ratios and under rapid braking con- ditions .

4) Determine the bicycle payload by weighing the on-bicycle test equipment

and rider. Record the weights.

5) Measure and record the wheel base of the bicycle. This measurement

is made from the center of the front axle to the center of the rear

axle.

4.1 Set-up for Primary Handbrake Lever

1) Adjust the position of the brake lever on the handlebar so that the

lever will be pulled vertically by the action of the force gage during

testing. This may involve changing the location of the levers on

the handlebars such that they are generally below the lowest part

of the handlebar (Figure 6),

2) Tighten the clamp to the lever, 25 mm (1 in) from the lever end (Figure

6).

3) Adjust the stops on the force gage to apply a maximum of 178 N (40

Ibf) to the brake lever. If the clamp bottoms against the handlebar.
at a load less than 178 N (40 Ibf), adjust the position of the clamp

on the lever to insure that the lever bottoms against the handlebar.

4) Adjust the length of the linkage from the force gage to the clamp

so that the brake system is fully relaxed and no braking forces are being applied to the brake levers.

5) Tighten the clamp of the force gage to the handlebar.

6) Make a final adjustment of the brakes according to the operating

instructions. No further brake adjustments are allowed by the re- gulation after this adjustment (1512.18(d)(2)).

7) Install the ground marker gun on the front fork of the bicycle (Figure

4), Strap the battery to the bicycle.

8) Connect the battery to the marker gun switches and guns.

9) Photograph the bicycle with the test hardware mounted on the bicycle.

10) Wipe the braking surface of the tire rims with alcohol to remove

any residue from earlier bicycle use.

4.2 Set Up for Extension Hand Brake Lever

1) Adjust the position of the extension lever on the handlebar so that

the lever will be pulled vertically by the action of the fingers

during testing.

2) Install the firing switch on the extension lever and the ground

marker gun on the fork.

3) Make a final brake adjustment according to the manufacturer's operating

instructions

.

4) Install the battery and necessary wiring.

5) Photograph the bicycle with the test hardware mounted on the bicycle.

6) Wipe the braking surface of the tire rims with alcohol to remove

any residue from earlier bicycle use.

4,3 Set Up for Coaster Brake Systems

1) Install the ground marker gun on the bicycle fork.

2) Install the firing switch on the seat tube so that the chain re- versal caused by the braking action causes the switch to catch in

the chain, and actuate the switch (Figure 7).

5
3) Install the battery and necessary wiring.

4) Photograph the bicycle.

4.4 Testing

The following tests shall be performed on all bicycles. The test

sequence will be in accordance with the flow diagram (Figure 1). For

a detailed procedure for bicycle brake testing see a Procedure for Testing

Bicycle Braking Performance [2]. A sample data sheet for recording the

braking test information is shown in Figure 8.

4.4.1 Handbrake Loading Test

On all bicycles equipped with handbrake levers and/or extension

levers, perform the Handbrake Loading (1512.18(d)(2)(i )) by applying

445 N (100 Ibf) to the brake levers or by bottoming the hand levers

against the handlebars, whichever comes first. This test may require

removal of the stops on the force gage (Figure 6 ) to allow full travel

of the gage. This load shall be applied and removed 10 times.

4.4.2 Rocking Test

On all bicycles equipped with handbrake levers and/or extension

levers, perform the Rocking Test (1512.18(d)(2)(iii )) by placing the

test rider on the bicycle and, with the brakes loaded as in the Loading

Test, drag the bicycle 6 times forward and 6 times rearward for a distance

of 75 mm (3 inches) each way,

4.4.3 Performance Test

1) Set the stops on the force gages to 178 N (40 Ibf) applied to the

brake lever and adjust the switches on the marker guns so that the

guns fire upon first actuation of the brake levers and at 178 N

(40 Ibf) or the maximum load.

2) Set up the elapsed timer and triggering tape switch on the test

pavement.

3) Load the ground marker guns.

4) Conduct stopping runs according to the Handbrake Performance Test

(1512.18(d)(2 )(v)) while traveling in opposite directions across

the timing switch.

5) Measure the stopping distance from the rearmost ground mark to the

corresponding gun on the bicycle. Make the measurement along the

original line of travel of the bicycle. Disregard the changes in

path line which occur during the test.

6
6) Compute the stopping distance, making the corrections for bicycle

velocity and payload. A sample calculation is shown in Figure 9,

5. TEST RESULTS

The specimen parameters for the 15 bicycles tested are given in

Table 1, The stopping distances for the bicycles measured during this

evaluation of the test method are given in Table 2. It is estimated

that the errors in the measurement of elapsed time did not exceed 0.0001

seconds, and that the errors in stopping distance measurement did not

exceed 0.03 m (0.1 ft).

6. DISCUSSION

It should be noted early in this discussion that the apparatus

assembled for these tests is not unique. Several alternate ways of measuring the lever forces or bicycle velocity could have been devised.

A further note about rider safety is necessary here. These tests are performed at relatively high speeds on a paved surface. There exists

a danger of an accident, resulting in possible injury to the rider.

Accidents occurred during testing of four of the fifteen bicycles used

in this program. It is significant that every test rider had at least one accident. After these accidents, several of the riders declined

to test another bicycle.

6.1 Loading and Rocking Tests

In general, the flow (Figure 1) and procedures for these two tests

and the performance test are not specified in the proposed regulation

and evolved during the test evaluation and hardware development period.

All bicycles equipped with handbrakes were tested for compliance

with the loading test and rocking test. All bicycles passed these tests

with the exception of bicycle 9. One of the brake pads on the front

caliper of this bicycle was dislodged from its holder during the rocking test. The pad was replaced in the holder, and the rocking test was repeated with no further failures.

6.2 Braking Tests

Tests were performed on 15 bicycles equipped with many of the handbrakefootbrake combinations currently available. A recurrent problem throughout

these tests was the difference in equipment and arrangement among the

several bicycles. To some extent, every bicycle tested became a separate

project

7
As was indicated above in section 4.4.3, the bicycle stopping distance of interest has been interpreted to be the straight Line distance

from the first ground mark to a point opposite the marker gun along

the original line of travel of the bicycle. This distance was chosen

instead of the distance along the path over which the bicycle traveled

during the stop, because it is the shorter of the two distances and

represents the minimum distance needed to stop during an emergency situation. In addition to the measured stopping distance, table 2 shows

the stopping distance corrected by adjusting the bicycle speed to 24

km/h (22 fps) and the bicycle payload to 68.1 kg (150 lb).

It was necessary to make the velocity correction because the weight

allowance provided for in the regulation assumes that the bicycle is

moving at 24 km/h (15 mph).

In addition, the percent variation in the corrected stopping distances

is shown. Most of the bicycles tested were capable of meeting the acceptance

criteria of the regulation after the above two adjustments to the stopping

distance had been made. The percent variation in stopping distance after

these adjustments ranged from 8 percent to 144 percent. Three bicycles

failed to stop from the required speed within 4,5 m (15 ft).

An analytical study of these and other variables which affect these

tests is presently being carried out [3]. This study contributed to

these procedures in the areas of data reduction and in the averaging

of the effects of weather and pavement. The data from these tests will

be used in the evaluation of the analysis.

6.3 Coefficient of Friction and Effect of Pavement Surface

A coefficient of friction measurement of two different test surfaces

was made using one bicycle. The stopping distance of this bicycle on these surfaces under nominally identical conditions was compared.

The coefficient of friction was measured by locking the rear wheel

of the bicycle. With 45.4 kg (100 lb) of weights placed on the seat,

the force exerted on the ground by the rear wheel was measured. A force

gage was attached to the rear tire near the ground and a gradually increasing

horizontal force was applied until the tire slipped on the pavement.

The two surfaces tested in this way were the paved parking lot which

was normally used for testing, and an unpainted, smooth concrete laboratory floor. The results of these tests are shown in Table 3.

6.4 Rider Reaction Times

As was discussed above, several bicycles were instrumented to measure

the brake force application time and the left-right coordination of

the brake handles. The results of these tests are given in Table 4.

8
These times are within the range of times reported for similar testing

at other laboratories.

6.5 Effect of Rider height

As can be seen from Table 2, tvo bicycles were tested by several

riders of different weights. The results from these tests are inconclusive.

\>rhile the raw stopping distances tended to be longer for the heavier

rider, as expected, the corrected distances did not show such a trend.

This can be seen best in the data reported for bicycle 8 tested with

extension levers.

7. CONCLUSIONS

The tests on brake systems proposed for the mandatory Requirements

for Bicycles have been performed on several representative samples.

A mathematical adjustment of the actual test speed of the bicycle to

24 km/h (15 mph) should be permitted by the regulation before the

weight allowance correction is made to the stopping distance for the

proper evaluation of the braking performance by these tests. Twenty

percent of the specimens failed to stop within the required distance.

All of these were equipped with caliper brakes on both wheels. An analytical

study which discusses the effect of many variables on stopping distance

is being developed. A danger of injury to the test rider exists during

the performance tests and future efforts might be made toward replacement

of this, and possibly the other brake tests, with a simpler, laboratory

procedure

.

9
8. REFERENCES

The documents which are applicable to these tests include:

1. Requirements for Bicycles, Part 1512, Federal Register, Vol. 39

No. 137, July 16, 1974, and its admendments.

2. Marlowe, D. E., A Procedure for Determining Bicycle Braking Per

formance, NBSIR 75-953, in preparation.

3. Mordfin, L., The GPSC Road Test of Bicycle Braking Performance

- Kinetic and Error Analysis, NBSIR 75-786, in preparation.

10
Bicycle Assembly

According to

Manufacturers

Instructions

Famil iarization

Ride

for Test

Rider

Payload

Determination

and

Wheel Base

Measurement

Installation

and Adjustment

of Test

Equipment

Famil iarization

Ride for Test

Rider

Final Brake

Adjustment

Perform Brake

Loading Test

(1512.18rd)(2)(i))

Perform Rocking

Test

(1512.18(d)(2)

iii))

Set up

Timer

Perform

Performance

Test

(1512.18(d)(2)(v))

Figure 1 - Flow Diagram for Handbrake Tests
Figure 3 - Loading Apparatus on a Bicycle
Figure 5 - Velocity-Timer Apparatus
Figure 7 - Firing Switch for Coaster Brakes
BRAKING TEST DATA SHEET

PREPARE ONE FOR EACH BICYCLE

a) Bicycle Manufacturer b) Test Date

Serial No. c) Rider

Model No.

d) Bicycle Information e) Test Information

Wheel Size in Wheel Base

Max Gear Ratio Equip. Weight Ibf

Brake Type Rider Weight Itrf

Brake Mfg.

Frame Size i_n

f) Loading Test g) Rocking Test

Load on Force Gage Ibf Pass-Fail

Lever Hit Bar

Pass-Fail

h) Performance Test

Stopping

Elapsed Distance Distance Between

Time from Markers

Run for Speed Direction Rear most L-R Application

No. Measurement of Run Marker Coordination of 40 Ibf Skidding

sec ft ft ft

Figure 8 - Braking Test Data Sheet
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APPENDIX

This appendix contains the engineering drawings for the test fixtures

designed for these tests and the parts list of all equipment used.

USCOMM NHS-OC
NBS-114A (REV. 7-73)

U.S. DEPT. OF COMM. BIBLIOGRAPHIC DATA

SHEET

1. PUBLIC ATION OR REPORT NO. NBSIR 75-755

2. Gov't Accession

No.

3. Recipient's Accession No.

4. TITLE AND SUBTITLE

The CPSC Road Test of Bicycle Braking Performance - Experimental Evaluation

5. Publication Date August 1975

6. Performing Organization Code

7. AUTHOR(S) 8. Performing Organ. Report No. NBSIR 75-755

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Proiect/Task/Work Unit No. 21305A0

11. Contract/Grant No.

12. Sponsoring Organization Name and Complete Address (Street, City, State, ZIP)

Office of Consumer Product Safety

Center for Consumer Product Technology

Institute for Applied Technology — National Buraau of Standards

13. Type of Report & Period Covered

Final

14. Sponsoring Agency Code

16. ABSTRACT (A 200-word or less factual sunwiary of most significant information. If document includes a significant

bibliography or literature survey, mention it here.) The brake performance criteria to be published as part of a mandatory regulation on bicycle safety requirements has been evaluated. Fifteen bicycles were

tested in accordance with the regulation. A mathematical adjustment of the actual

test speed of the bicycle to 24 km/hr (15 mph) is necessary before the weight allowance can be made to the stopping distance in the evaluation of these tests.

A danger of injury to the test rider exists during the tests and future efforts shou

be made toward replacement of these tests with a simpler laboratory procedure.

17. KEY WORDS (six to twelve entries; alphabetical order; capitalize only the first letter of the first key word unless a proper name; separated tiy semicolons

)

Bicycles; braking; consumer safety; handbrake; safety; testing

18. AVAILABILITY |Xg Unlimited 19. SECURITY CLASS

(THIS REPORT)

21. NO. OF PAGES

1 1 For Official Distribution. Do Not Release to NTIS

UNCL ASSIFIED

32

1 1 Order From Sup. of Doc, U.S. Government Printing

Washington. D.C. 20402. SD Cat. No. C13

Office 20. SECURITY CLASS

(THIS PAGE)

22. Price

fx! Order From National Technical Information Service

Springfield, Virginia 22151 (NTIS)

UNCLASSIFIED $3.75

USCOMM-DC 29042-P'
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