NBSIR 75-953

A Procedure for Determining

Bicycle Braking Performance

Donald E. Marlowe

Engineering Mechanics Section

Mechanics Division

Institute for Basic Standards

National Bureau of Standards

Washington, D. C. 20234

Final Report

December 1975

Issued, July 1976

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 75-953

A PROCEDURE FOR DETERMINING

BICYCLE BRAKING PERFORMANCE

Donald E. Marlowe

Engineering Mechanics Section

Mechanics Division

Institute for Basic Standards

National Bureau of Standards

Washington, D. C. 20234

Final Report

December 1975

Issued, July 1976

Prepared for Office of Consumer Product Safety

Center for Consumer Product Technology

Institute for Applied Technology

National Bureau of Standards

Washington, D. C. 20234

U.S. DEPARTMENT OF COMMERCE, Elliot L. Richardson, Secretary

Edward O. Vetter, Under Secretary

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

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Acting Director

CONTENTS

page

1. SCOPE

1.1 General 1

1.2 Test Samples 1

1.3 Test Flow 1

2. APPLICABLE DOCUMENTS 1

3. TEST EQUIPMENT 3

4. TEST PRECAUTIONS 3

4.1 Environment 3

4.2 Rider Safety 3

4.3 Equipment Check-out 3

5. PROCEDURES

5.1 Preliminary Checks and Measurements 5

5.2 Test Equipment Setup 5 5.2.1 Caliper Brake System 6 (a) primary system 6

(b) extension lever system 11

5.2.2 Coaster Brake System 11

5.2.3 Caliper-Coaster Brake Combinations 16

5.3 Final Checks and Adjustments 16

5.4 Compliance Test Procedure 16

5.4.1 Loading Test 16

5.4.2 Rocking Test 18

5.4.3 Performance Test 18

5.4.4 Rider Coordination 21
LIST OF FIGURES

1. Flow diagram of test procedures.

2. Test setup for measurement of coefficient of friction.

3. Velocity timer setup.

4. Force gage assembly.

5. Lever clamp of force gage prior to actuation.

6. Force shall be applied along the line of action of the

force gage after actuation.

7. Limit stops and switches on the force gage.

8. Lever clamp adjusted to allow the lever to bottom against

the handlebar.

9. Ground marker gun.

10. Schematic of marker gun firing circuit.

11. Test setup for extension lever.

12. Test setup for coaster brake.

13. Bicycle performance test sample calculation.
A PROCEDURE FOR DETERMINING BICYCLE

BRAKING PERFORMANCE

Donald E. Marlowe

ABSTRACT

A procedure which could be used to determine

bicycle braking performance for compliance with

the Federal Bicycle Safety Regulation, Requirements

for Bicycles, has been developed. The procedure

includes tests for brake system integrity and

stopping distance performance. Sample data collection sheets and calculations are given.

Key Words: Bicycles, braking, consumer safety,

handbrakes , t es t ing

.

1. SCOPE

1.1 General

This procedure was used for the testing of bicycles in accordance

with paragraph 1512 . 18 (d) (2) (i) Loading Test, paragraph 1512 . 18 (d) (2) (iii)

Rocking Test, and paragraph 1512. 18 (d) (2) (v) Performance Test of the

Federal Bicycle Safety Regulation, Requirements for Bicycles, Federal

Register , July 16, 1974, and its amendments.

1.2 Test Samples

Bicycles which are proposed for sale on the retail market were

tested for brake performance using the test procedure with the equipment

outlined below or its equivalent.

1.3 Test Flow

The flow of procedures which were followed in the tests is shown

in Figure 1.

2. APPLICABLE DOCUMENTS

The documents which are applicable to these tests are:

Requirements for Bicycles, Part 1512, Federal

Register , Vol. 39, No. 137, July 16, 1974; as amended, Federal Register , Vol. 40, No. 220,

November 13, 1975.
Bicycle Assembly

According to

Manufacturers

Instructions

Set Up

Interval

Timer

Installation

and Adjustment

of Test

Equipment

Perform Brake

Loading Test

(1512.18(d) (2) (i))

Familiarization

Ride

for Test

Rider

Measure the

Coefficient of

Friction Between

The Test Tire

And Pavement

Familiarization

Ride for Test

Rider

Clean Tire

Rims and

Photograph

the Bicycle

Perform Rocking

Test

(1512.18 (d)(2)(iii))

Payload

Det erminat ion

and

Wheel Base

Measurement

Final Brake

Adjustment

Readjust

Force Gage Stops

and Switches

Load the

Ground Marker System

Perform

Performance

Test

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

Compute the

Bicycle Speed

and Stopping

Distance

Fig. 1 Flow Diagram of Test Procedures
Mordfin, L. , The CPSC Road Test of Bicycle Braking

Performance - Kinetic and Error Analysis , NBSIR 75-

786, October 1975.

Marlowe, D. E. , The CPSC Road Test of Bicycle

Braking Performance - Experimental Evaluation , NBSIR 75-755, August 1975.

3. TEST EQUIPMENT

Tests were performed using the test equipment listed in Table 1 or its equivalent.

4 . PRECAUTIONS

4 . 1 Environment

(1) All testing was performed on a dry, clean, smooth paved surface free from protruding aggregate. The coefficient of friction

between the tire and test surface was always less than 1.0 as determined

on the bicycle being tested (see section 4.3). The pavement had a slope

of less than one percent.

(2) The wind velocity during the tests did not exceed 11 km/hr

(7 mph)

.

4.2 Rider Safety

(1) All riders were equipped with a riding helmet and clothing to

limit the degree of injury should an accident occur during testing.

Suitable clothing should include abrasion resistant pants, jacket and

gloves similar to those used by professional motorcycle riders.

(2) The rider was encouraged to gain familiarity with the performance characteristics of the test bicycle. The familiarization took

place with the bicycle equipped for testing. Several test runs,

similar to the performance test run, but at lesser speeds, were made.

4.3 Equipment Check-out

(1) The coefficient of static friction between the bicycle and

test surface was measured. A weight of 68.1 kg (150 lb) was placed on

the bicycle seat. The weight distribution of the bicycle was determined

by placing a platform scale or load cell weighing system under each

wheel. The rear wheel of the bicycle was locked to prevent its rotation.

A force gage was attached to the locked wheel near the tire-pavement

interface. Steadily increasing forces were applied to the wheel in a direction parallel to the test surface until the wheel began to slide on

the surface. The coefficient of friction between the tire and pavement

is the ratio of the maximum tractive force parallel to the surface to

the load distributed onto the rear wheel.

3
Table 1 - Test Equipment for Bicycle Braking Tests

Item

No. Description

1. Tire inflation pressure gage, 7 x 10 5 N/m2

, (100 psi) capacity.

2. Steel tape measure.

3. Scales-91 kg (200 lb) capacity.

4. 68.1 kg (150 lb) mass (rider dummy)

5. Force gage - 900 N (200 lbf) capacity.

6. Rear wheel loading fixture.

7. Rear wheel locking pin.

8. Electronic timer.

9. Tape switch, 2m (6 ft) length.

10. 12 volt rechargeable battery, (2), with charger.

11. Force gage assembly with marker system firing switches.

12. Force gage - 450 N (100 lbf) capacity, (2).

13. Ground marker gun with marker loads.

14. Wiring for marker gun.

15. Extension lever stops.

16. Tape switch, 5 cm (2 in) length for actuating marker gun.

17. Firing switch for coaster brakes.

18. Riding helmet.

19. Riding gloves.

20. Riding coveralls.

21. Alcohol and rag.

22. Camera.

23. Data sheet.

4
(2) Batteries for the ground marker system and velocity timer were

fully charged at the start of testing.

(3) Bicycle tires were inflated to the pressure recommended by the

tire manufacturer and molded into the tire sidewall.

5. PROCEDURE

The test procedures described in the following sections are not

unique and were determined somewhat by the equipment available at the

time the tests were conducted. These tests were designed to evaluate

the structural integrity of the braking system (Loading Test and Rocking

Test) , to insure that the coefficient of static friction between the

tire and test pavement is within acceptable limits, and to evaluate the

dynamic stopping capability of the bicycle (Performance Test) . The

braking systems to be tested using these procedures include those

actuated from primary hand brake levers, from auxiliary or extension

hand lines, and from foot pedals.

5.1 Preliminary Checks and Measurements

STEP DESCRIPTION

1. Fully assemble the bicycle using the instructions provided by its

manufacturer.

2. Adjust all brake and shift linkages in accordance with the

instructions

.

3. Inflate the tires to the maximum pressure recommended by their

manufacturer

.

4. Ride the bicycle to insure that all adjustments are properly made.

5. Measure the wheel base of the bicycle. This measurement is made

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

to the nearest 0.1 cm (0.05 in). Record the wheel base on the

data sheet (Table 2).

6. Weigh the test equipment. Record the weight (Table 2).

7. Weigh the rider. Record the weight (Table 2).

8. Affix a 68.1 kg (150 lb) mass to the bicycle seat.

9. With the bicycle level and upright, measure the ground force at

the rear wheel. Record the weight (Table 2).

10. Position the bicycle on the test pavement in the vicinity of the

expected stopping tests.

5
11. Attach the force gage to the rear wheel of the bicycle near the

ground (Fig. 2).

12. Lock the rear wheel to prevent its rotation (Fig. 2). The front

wheel must be free to rotate.

13. Using the force gage, apply steadily increasing forces to the

wheel, parallel to the test pavement and in the plane of the

wheel. Continue loading until the tire slides on the pavement.

Record the maximum force (Table 2).

14. Compute the coefficient of friction for the particular tire-pavement combination as the ratio of the maximum applied force (item 13)

to the weight on the rear wheel (item 9).

15. Verify that the above coefficient of friction is less than

1.0 (1512.18(d) (2) (v)(i)).

16. Remove the test mass from the bicycle.

17. Connect the external power plug to the electronic interval timer.

18. Connect the triggering tape switch to the battery (Fig. 3).

19. Connect the battery package to the timer.

20. Position the triggering tape switch across the test pavement.

5.2 Test Equipment Setup

5.2.1 Caliper Brake System

5.2.1(a) Primary Brake System

STEP DESCRIPTION

1. Remove all handgrips, wrapping tape, end plugs, etc., from the

handlebars.

2. Position the force gage assembly on the handlebars and fasten

with the friction clamp (Fig. 4).

3. Attach the lever clamp to the brake lever so that the center

of the clamp is 25 mm (1 in) from the lever end (Fig. 5).

4. Adjust the position of the brake lever on the handlebar such

that the line of action of the force gage will be straight when

the lever is fully depressed. (Fig. 6)

5. Using the force gage assembly, apply 445 N (100 lbf) to the

hand brake lever.

6
Table 2 - Braking Test Data Sheet

a) Bicycle Manufacture^

Serial No.

Model No.

d) Bicycle Information

Wheel Size

Max Gear Ratio

Brake Type

Brake Mfg.

Frame Size

f) Loading Test

Load on Force Gage_

Lever Hit Bar

Pass-Fail

m

lbf

lbf

b) Test Data_

c) Rider

e) Test Information

Wheel Base in

lbf

lbf

Equip. Weight

Rider Weight

g) Rocking Test

Pass-Fail

i) Coefficient of Friction

Bicycle weight lbf

Force applied to

wheel lbf

h) Performance Test

Run

No.

Elapsed

Time

for Speed

Measurement

Direction

of Run

Stopping

Distance

from

Rear Most

Marker

Distance Between

Markers

L-R Application

Coordination of 40 lbf Skidding

sec ft ft ft

7
Fig. 3 Velocity timer setup

8
9
Fig. 6 Force shall be applied along the line of action

of the force gage after actuation.

10
6. Adjust the stops (Fig. 7) on the force gage assembly to limit the

applied force to a maximum of 445 N (100 lbf )

.

7. If the clamp bottoms against the handlebar at a load less than

445 N (100 lbf), readjust the position of the clamp (Fig. 8).

8. Remove the 445 N (100 lbf) load from the brake system.

9. Adjust the length of the force gage clamp linkage to insure that

the brake system is fully unloaded and no braking forces are being applied to the braking system.

10. Install the ground marker gun on the front fork of the bicycle

(Fig. 9).

11. Strap or tape the ground marker system battery to the bicycle

in any convenient location (Fig. 4).

12. Connect the wiring to the battery, gun and firing switches on

the force gage assembly (Fig. 10).

13. Connect the ground wire from the marker gun to the battery.

5.2.1(b) Extension Lever System

STEP DESCRIPTION

1. Install the extension lever stops on the handlebar.

2. Adjust the position of these stops so that the extension lever

travel beyond the top surface of the handlebar is prevented

(Fig. 11).

3. Install the ground marker gun on the front part of the bicycle

(Fig. 9).

4. Strap or tape the ground marker system battery to the bicycle

in any convenient location (Figs. 4 & 11).

5. Install the firing switch on the extension level (Fig. 11).

6. Connect the battery to the switch and gun (Fig. 10).

7. Connect the ground wire from the gun to the battery.

5.2.2 Coaster Brake System

STEP DESCRIPTION

1. Install the ground marker gun on the front fork of the bicycle

(Fig. 9).

2. Strap or tape the ground marker system battery to the bicycle

in any convenient location (Figs. 4 & 11).

11
Fig. 7 Limit stops and switches on the force gage
Fig. 9 Ground marker gun

13
Fig. 10 Schematic of marker gun firing circuit

14
Fig. 11 Test setup for extension lever

15
3. Install the firing switch on the seat tube (Fig. 12) so that

any rearward motion of the chain causes the switch to close.

4. Connect the battery through the switch to the gun.

5. Connect the ground wire from the battery to the gun.

5.2.3 Caliper-Coaster Brake Combinations

To conduct tests on these systems, use procedures discussed above

in sections 5.2.1 and 5.2.2 of the procedure. Both systems must be

tested simultaneously.

5.3 Final Checks and Adjustments

STEP DESCRIPTION

1. Check the rider's safety equipment. The rider shall wear a riding helmet and leather gloves plus a pair of durable coveralls or other riding attire.

2. Familiarize the rider with the behavior characteristics of the

bicycle as it is equipped for the performance tests. This shall

include several stops similar to those needed in the performance

test but from lower speeds.

3. Adjust all brake system linkages and clearances in accordance

with the manufacturer's instructions. This is the final adjustment which is permitted under the regulation (1512.18(d)(2)).

4. Wipe the tire rims of the bicycle using a clean cloth dampened

with alcohol to remove any residue from earlier bicycle use.

5. Photograph the bicycle as it is set up for testing.

6. Turn on AC power to the interval timer.

5.4 Compliance Test Procedure

5.4.1 Loading Test

All bicycles equipped with hand brakes (primary and/or extension

levers) are to be tested in accordance with the Hand Brake Loading

Test (1512.18(d) (2) (i)) of the regulation using the procedure as follows

:

STEP DESCRIPTION

1. Using the force gage loading apparatus, apply load to the

hand brake lever to a maximum of 445 N (100 lbf) or until the

hand brake bottoms against the handlebar, whichever occurs

first. Release the load.

16
Fig. 12 Test setup for coaster brake

17
2. Repeat for a total of ten tests.

3. Repeat steps 1 and 2 for the extension lever system, if any.

4. Visually inspect the braking system after testing for fractures,

failures, or misalinements which result from the test.

5. Record the results (Table 2).

5.4.2 Rocking Test

All bicycles equipped with hand brakes (primary and/or extension lever) are to be tested in accordance with the Rocking Test

(1512.18(d) (2) (iii)) of the regulation using the procedure as follow:

STEP DESCRIPTION

1 Affix a 68.1 kg (150 lb) mass to the bicycle seat.

2. Position the bicycle on the test surface.

3. Using the force gage loading apparatus, apply load to the hand

brake lever to a maximum of 445 N (100 lbf) as in the loading test

above (section 5.4.1, step 1).

4. Drag the bicycle forward and rearward over the test surface for

a total distance of 8 cm (3 in) in each direction.

5. Repeat for a total of 6 tests.

6. Visually inspect the braking system after testing for loosening

of the brake pads, pad holder, or cable and hand-lever securing

devices

.

7. Remove the 68.1 kg (150 lb) mass from the bicycle.

8. Record the results (Table 2).

5.4.3 Performance Test

All bicycles are to be tested in accordance with the Performance

Test (1512.18(d) (2) (v)) of the regulation using the procedure as follows

:

STEP DESCRIPTION

1. On bicycles equipped with hand brakes adjust the stops on the

force gage assembly (Fig. 7) or the extension lever (Fig. 11) to

limit the applied force to a maximum of 180 N (40 lbf)

.

2. Adjust the position of the firing switches (Fig. 7) so that the

marker guns fire upon first actuation of the brake lever.

18
3. Load the ground marker guns with the paint cartridges.

4. Set the elapsed timer to zero.

5. Accelerate the bicycle to the specified test speed. Insure that

the bicycle is traveling in a straight line at the test speed as

it crosses the timing tape switch, and that the test rider is in

the normal riding position. The test rider must remain in the

normal riding position throughout the test.

6. Using the brake system(s) under test, stop the bicycle as rapidly

as possible.

7. Note the presence of front wheel lockup, if any. A test run

is invalid if front wheel lockup occurs.

8. Measure the stopping distance from the center of the rearmost

ground marker along the original line of travel of the bicycle

to the point opposite the center of the ground marker guns,

disregarding changes in path which occur during the test.

Record the distance (Table 2)

.

9. Record the elapsed time of the bicycle from the interval timer

(Table 2).

10. Repeat steps 3 through 8 for a minimum of 4 test runs.

11. Compute the bicycle speed and corrected stopping distance using

the equations and following the example shown in Fig. 13.

Corrections for velocity at the initiation of braking may be

made. The corrected braking distance shall be computed as follows

S =

c

where

S

c = Corrected braking distance,

V

a

= Specified test velocity,

V = Measured test velocity,

m

S = Measured braking distance,

m

The test run is invalid if at the commencement of the test, the

measured test speed of the bicycle is not less than nor greater

than the test speed required by this Part 1512 by 1.5 km/h (0.9 mph)

.

The stopping distances specified are based on a rider weight

of at least 68.1 g (150 lb) and a maximum rider and weight combination of 91 kg (200 lb). Greater stopping distances are allowable

for heavier riders and test equipment weights at the rate of 0.30 m

per 4.5 kg (1.0 ft per 10 lb).

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5.4.4 Rider Coordination

On bicycles equipped with hand brake systems, it may be desirable

to measure the actuation time of the braking system, i.e., the time

from first actuation of the brake to the time the applied lever force

equals 178 N (40 lbf ) . Similarly, it may be desirable to measure the

rider coordination in actuating the brake levers, or for bicycles

equipped with a single hand brake and coaster brakes, the time difference between actuation of these two systems. In these cases, the

second chamber of the ground marker gun can be wired to the battery

(see Fig. 10), and the firing switch adjusted to measure the desired

parameter. A second ground marker gun can be mounted on the bicycle

to permit various measurements to be made during a single test. For

these measurements, assume a constant bicycle speed between the ground

marks and calculate the resulting elapsed time. Record the distance

between ground marks in Table 2.

21

NBS-114A (Rev. - 73)

ii c ic dt fir r~ r\ ki u BIBLIOGRAPHIC DATA

SHEET

1. PUBLICATION OR REPORT NO. NBSIR 75-9532. Gov't Accession

No.

3. Recipient's Accession No.

4. TITLE AND SUBTITLE

A PROCEDURE FOR DETERMINING BICYCLE BRAKING PERFORMANCE

5. Publication Date December 1975

o. Performing Organization Code

7. AUTHOR(S) 8. Performing Organ. Report No. NBSIR 75-953

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Project/Task/Work Unit No.

11. Contract/Grant No.

\i. sponsoring Organization Name and Complete Address (Street, City, State, ZIP)

Same as No. 9

13. Type of Report & Period Covered Final

14. Sponsoring Agency Code

15. SUPPLEMENTARY NOTES

16. ABSTRACT (A 200-word or less [actual summary of most significant information. If document includes a significant

bibliography or literature survey, mention it here.)

A procedure which could be used to determine bicycle braking performance

for compliance with the Federal Bicycle Safety Regulation, Requirements for

Bicycles, has been developed. The procedure includes tests for brake system

integrity and stopping distance performance. Sample data collection sheets

and calculations are given.

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

Bicycles; braking; consumer safety; handbrakes; testing.

18. AVAILABILITY [^Unlimited

1 1 For Official Distribution. Do Not Release to NTIS

1 I Order From Sup. of Doc, U.S. Government Printing Office Washington. D.C. 20402. SD Cat. No. C13

LxJ Order From National Technical Information Service (NTIS)

Springfield, Virginia 22151

19. SECURITY CLASS

(THIS REPORT)

UNCL ASSIFIED

21. NO. OF PAGES

25

20. SECURITY CLASS

(THIS PAGE)

UNCLASSIFIED

22. Price

$3.50

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