Bsi bs au 050 1 1 3 1993 (1999) iso 8767 1992

BRITISH STANDARD AUTOMOBILE SERIES BS AU 50 1 3 1993 ISO 8767 1992 Tyres and wheels — Part 1 Tyres — Section 1 Car tyres — Subsection 1 3 Method of measuring rolling resistance Reproduced by IHS under[.]

ISO 8767:1992

This Bri shStan ard, ha ing

b en pre ared u der the

directonof the Automo ile

Stan ards Policy Commi e ,

waspublished u der the

authoriyof the Stan ards Bo rd

an comes into efect on

1 J n ary1 9

© BSI1 -1 9

The folowing BSI references

relate to the work on this

stan ard:

Commi e reference AUE/4

Draft for comment8 / 73 9 DC

ISBN 0 5 0 2 5 2 9

The prep ration of this BritishStand rd was entrusted b the Automobi e

Stand ards Pol cy Commit e ( AUE/-) to Tech ical Commit e AUE/4, upon

which the fol owing bod ies were represented :

Ag ricultural Eng ine r ’ Association

Automobi e Association

British Industrial Truck Association

British Pres ure Gaug e Man facturer ’ Association

British Rub er Man facturer ’ Association

Bus and Coach Cou ci

Dep rtment of Transport

Freig ht Transport Association

Institute of Road Transport Eng ine r ( Inc)

Motor Cy cle Ind ustry ’s Association of Great Britain Ltd

Motor Ind ustry Resear h Association

National Ty re Distributor ’ Association

Retrea Man facturer ’ Association

Roa Haulag e Association Ltd

Society of Motor Man facturer and Tra er Ltd

Am endm ents is ued sinc publ cation

Pag e

Annex C ( informativ e) Measurement method s of

moment of inertia for drum and ty re as embly —

Fig ure 1 — Fre -bod diag ram of ty re/drum sy stem,

National foreword

This S bsection of this Part of BS AU5 has be n prep red u d er the direction

of the Automobi e Stand rds Pol cy Commit e and is identical with

ISO8 6 :19 2 Pa ss nger ca r tyr es — Method s o mea sur ing r oling r esista nc ,

publshed b the International Org anization for Stand rdization ( ISO) Other

Parts of this stand rd are as fol ows:

— Pa r t2: Whe ls a nd r ims;

— Pa r t3: Va lve ;

— Pa r t4: R im pr ofie a nd d imensions

A British Stand ard d oes not purport to includ e al the neces ary prov isions of a

contract User of British Stand rd s are responsible for their cor ect a plcation

Com pl anc with a British Standard does not ofitself confer im m unity

f om leg al o l g ations

Sum mary of pag es

This document comprises a f ont cov er, an insid e font cov er, p g esi andi ,

p g es1 to8 an a b ck cov er

This stand rd has be n up ated ( se copy rig ht d ate) an ma hav e ha

amendments incorporated This wi l be indicated in the amendment ta le on the

inside f ont cov er

1 Scope

This International Stand rd specifies methods for

measuring rol ing resistance, u d er controled

la oratory conditions, for new pneumatic ty res

desig ned primari y for use on p s eng er car The

relationship betwe n v alues obtained and the fuel

economy of the v ehicle is undetermined, and such

v alues are not intended to be used to indicate lev els

of perormance or qualty

This International Stand rd a ples to al

p s eng er car ty res

It ena les comp risons to be mad e betwe n the

rol ing resistance of new ty res when they are

f e -rol ng straig ht ahea , in a position

perpendicular to the drum outer sur ace, and in

stea y -state conditions

In measuring ty re rol ng resistance, it is neces ary

to measure smal for es in the presence of much

larg er for es It is, therefore, es ential that

equipment and instrumentation of a propriate

ac uracy be used

2 Definitions

For the purposes of this International Stand rd , the

fol owing d efinitions a ply

2.1

roling resistanc : F

r

los of energ y ( or energ y consumed) per u it of

distance

NOT 1 The SI u i conv ntonaly used for the roling

resistance is the newton metre p r metre ( N·m/ m)

This is e uiv lent to the dra fore in newtons ( N)

2.2

roling resistanc coeficient: C

r

ratio of the rol ng resistance, in newtons, to the loa

on the ty re, in newtons This quantity is

dimensionles and is deriv ed as folows:

2.3

ca ped inflation

proces of inflating the ty re and alowing the

inflation pres ure to bui d up, as the ty re is warmed

up whie run ing

2.4

reg ulated inflation

proces of inflating the ty re to the required pres ure

independent of its temperature, and maintaining

this inflation pres ure whi e the ty re ru s u d er

load This is most commonly done b using a

reg ulated pres ure sour e at ached to the ty re

throug h a rotating union ( Se Annex B.)

2.5

parasitic los

los of energ y ( or energ y consumed) per unit

d istance excluding ty re los es, and at ributa le to

aerody namic los , bearing f iction and other sour es

of sy stematic los which ma be in erent in the

measurement

2.6

skim rea ing

ty pe of p rasitic los measurement, in which the

ty re is kept rol ing , without sl p p g e, whie

reducing the ty re loa to a lev el at which energ y los

within the ty re itself is v irtualy z ro

2.7

machine reading

ty pe of p rasitic los measurement, inv olv ing los es

of the test machine, exclusiv e of los es in the

rotating spindle which car ies the ty re and rim

2.8

moment of inertia

( se Annex C)

3 Test methods

The fol owing alternativ e measurement methods

are g iv en in this International Stand ard The choice

of an ind iv idual method is left to the tester For each

method, the test measurements shal be conv erted

to a rol ing resistance for e acting at the ty re/drum

inter ace

a) For e method: the reaction for e at the tyre

spindle

b) Torq ue method: the torque input to the test

drum

c) Power method: the power input to the test

drum

d) Deceleration method : the deceleration of the

test drum and ty re as embly

4 Test equipment

4.1 Drum spe ifications

4.1.1 Diamet er

The test dy namometer shal hav e a cy lindrical

fly whe l ( d rum) with a diameter of betwe n1,5m

and3m inclusiv e It should be noted that the

results are diferent; se 8.3 for drum diameter

cor ection for comp risons, if neces ary

4.1.2 Sur ac

The sur ace of the drum shal be smo th ste l or

textured an shal be kept clean For the textured

drum sur ace, se B.4

C

r rol ng resistance

test loa

=

4.1.3 Width

The width of the drum test surace shal ex ce d the

width of the test ty re tread

4.2 Test rim

The ty re shal be mou ted on a test rim, as specified

in Annex A

4.3 Lo d, al g nment, control and

instrum entation ac uracies

Measurement of these p rameter shal be

suficiently ac urate and precise to prov ide the

required test d ata The specific an respectiv e

v alues are shown in Annex A

4.4 Therm al environm ent

4.4.1 Referenc condit ions

The reference ambient temperature, as measured

on the rotational a is of the ty re,1 m awa f om the

plane touching the nearest ty re sidewal, shal

be25°C

4.4.2 Alternative condit ions

I the reference temperature can ot be obtained, the

rol ng resistance measurement shal be cor ected to

stand rd temperature cond itions in ac ord ance

with8.2

4.4.3 Drum sur ac temperat ure

Care should be taken to ensure that the

temperature of the test d rum sur ace is

a proximately the same as the ambient

temperature at the beg in ing of the test

5 Test conditions

The test consists of a measurement of rol ng

resistance in which the ty re is inflated and the

inflation pres ure al owed to buid up

( i.e “ ca pedair”)

5.1 Test spe ds

5.1.1 Single t est velocit y

The v alue shal be obtained at a drum v elocity

of8 km/h

5.1.2 Multiple t est velocity

The v alues shal be obtained at drum v elocities

of5 km/ h, 9 km/ h and1 0km/ h

5.2 Test lo d

The stand ard test loa shal be computed f om8 %

of the ma imum loa ca acity of the ty re and shal

be kept within the tolerance specified in Annex A

5.3 Test inflation pres ure

The inflation pres ure shal be the inflation

pres ure, specified b the ty re man facturer

concerned , cor espond ing to the ma imum ty re load

ca acity reduced b 3 kPa The inflation pres ure

shal be ca ped with the ac uracy specified inA.4.1

5.4 Duration and velocity

W hen the deceleration method is selected, the

fol owing requirements a ply :

a) for duration, %t, the time inc ements shal not

exce d0,5s;

b) any v ariation of the test drum v elocity shal not

exce d1km/h

5.5 Optional conditions

I the sensitiv ities of load , inflation or v elocity are

d esired, the a ditional information g iv en in

Annex B should be consulted

6 Test procedure

The test procedure steps des ribed below are to be

fol owed in the seq uence g iv en

6.1 Break- in

To ensure repeata i ity of measurements, an initial

break- n and co l ng period is req uired prior to the

start of the test Such a break- n should be car ied

out on a v ehicle or on a test d rum of at least1,5m

diameter for a period of at least1 h, at a minimum

v elocity of8 km/ h, with the loa an inflation

pres ure g iv en in5.2 and5.3 respectiv ely

6.2 Therm al conditioning

Place the inflated ty re in the thermal env ironment

of the test location for the time neces ary to achiev e

thermal eq ui ibrium which is g eneral y reached

after3h

6.3 Pres ure a justm ent

After thermal conditioning , the inflation pres ure

shal be a justed to the test pres ure, and

v erified10min after the a justment was mad e

6.4 Warm -up

The ty re shal be ru at constant test v elocity u ti

reaching a sta i z d stead y -state v alue of rol ing

resistance Recommend tions for warm-up periods

are g iv en in Annex B

6.5 Measurem ent and re ording

The folowing shal be measured an recorded

( se Fig ure 1):

a) test v elocity , U

n

;

b) loa on the ty re normal to the drum sur ace,

L

m

;

c) test inflation pres ure:

1) initial, as d efined in6.3,

2) final, for ca ped inflation;

d) the driv ing torque on the driv e shaft, T

t , the

ty re spindle for e, F

t , the input power, V×A , or

the d eceleration of the test drum/ty re/whe l

as embly , % Ê/% t, depending on the method;

e) distance, r

L ( se 7.2.1);

f) ambient temperature, t

mb

;

g ) test drum rad ius, R ;

h) test method chosen;

i test rim ( desig nation an material

6.6 Measurem ent of parasitic los es

Determine p rasitic los es b the procedure g iv en

in6.6.1 to6.6.3

6.6.1 Skim reading

a) Reduce the loa to maintain the ty re at the test

v elocity without sl p ag e to, for ex mple,5 N

b) Record the spindle for e, F

p , input torq ue, T

p ,

or the power, whichev er a ples

c) Record the loa on the ty re normal to the d rum

sur ace, L

p

6.6.2 Machine reading

a) Remov e the ty re f om the drum surace

b) At the test v elocity , U

n ,record the input torque,

T

p , the power, or the test drum d eceleration,

whichev er a ples

6.6.3 De elerat ion met hod

a) Remov e the ty re f om the test sur ace

b) Record the d eceleration of the test drum,

%Ê

o / % t, and that of the u loa ed ty re, %Ê

po /% t

7 Da ta interpr ta tion

7.1 Subtraction of parasitic los es

The p rasitic los es shal be subtracted as shown

in7.1.1, 7.1.2 or7.1.3

7.1.1 Skim reading

Subtract the skim rea ing f om the test

measurement

7.1.2 Machine reading

Subtract the machine rea ing fom the test

measurement

7.1.3 Parasit ic los e

Calculate the p rasitic los es, F

p , in newtons as

7.2 Rol ing resistanc calcula tion

The net v alues of d riv ing torq ue, spindle for e,

power or deceleration are to be conv erted to rol ng

resistance, F

r , ex res ed in newtons, using the

a propriate method, as shown in7.2.1 to7.2.4

Fig ure 1 — Fre - bo y diag ram oftyre/drum

system , as um ing no bearing and

windag elos es

where

I is the test drum inertia in rotation, in

ki og ram metres sq uared;

R is the test d rum sur ace ra ius, in metres;

Ê

vo

is the test drum ang ular v elocity , without

ty re, in ra ians per second;

% t

o

is the time inc ement chosen for the

measurement of the p rasitic los es

without ty re, in second s;

I

T

is the ty re and whe l inertia in rotation, in

ki og ram metres sq uared;

R

r

is the ty re rol ing ra ius, in metres;

Ê

po

is the ty re ang ular v elocity , u loa ed ty re,

in rad ians per second

7.2.1 Fo c method

The rol ing resistance, F

r , in newtons, is calculated

with the eq uation

F

r

=F

t

[ 1+( r

L /R )]

7.2.2 To que method

The rol ng resistance, F

r , in newtons, is calculated

with the eq uation

7.2.3 Power method

The rol ing resistance, F

r , in newtons, is calculated

with the eq uation

7.2.4 De eleration met hod

The rol ing resistance, F

r , in newtons, is calculated

with the eq uation

Annex C g iv es g uidelnes an practical ex amples to

measure the moments of inertia for the d eceleration

method

8 Data a na lysis

8.1 Roling resistanc coeficient

The rol ing resistance co ficient, C

r , is calculated b

div iding the rol ing resistance b the loa on the

ty re:

8.2 Tem perature cor e tion

I measurements at temperatures other than25°C

are unav oid ble ( only temperatures not les

than20°C not more than3 °C are ac epta le),

then a cor ection for temperature shal be ma e

using the fol owing eq uation, where F

r2

is the

rol ng resistance at25°C, in newtons:

F

r2

=F

r [1 +K(t

amb –25)]

8.3 Drum diam eter cor e tion

Test results obtained f om d iferent drum diameter

ma be comp red b using the fol owing the retical

formula:

F

r0

ÒKF

r0

with

where

F

t

is the ty re spindle for e, in newtons;

r

L

is the distance f om the ty re a is to the

d rum outer sur ace u der stea y -state

conditions, in metres;

R is the test drum ra ius, in metres

where

T is the input torq ue, in newton metres;

R is the test drum ra ius, in metres

where

V is the electrical potential a pl ed to the

machine driv e, in v olts;

A is the electric cur ent drawn b the

machine d riv e, in amperes;

U

n

is the test d rum v elocity , in ki ometres per

hour

where

I is the test d rum inertia in rotation, in

kiog ram metres sq uared;

R is the test d rum sur ace ra ius, in metres;

% t

v

is the time inc ement chosen for

measurement, in second s;

Ê

v

is the test drum ang ular v elocity , load ed

ty re, in rad ians per second ;

I

T

is the ty re an whe l inertia in rotation, in

kiog ram metres sq uared;

R

r

is the ty re rol ing ra ius, in metres;

M

AP

is the ty re aerod y namic torq ue;

F

P

is as defined in7.1.3

F

r

T

R

-=

F

r

3,6V×A

U

n

=

where

F

r

is the rol ing resistance, in newtons;

L

m

is the test loa , in newtons

where

F

r

is the rol ng resistance, in newtons;

t

mb

is the ambient temperature, in deg re s

Celsius;

K is equal to0,01 for car ty res

where

R

1

is the ra ius of d rum1, in metres;

R

2

is the ra ius of d rum2, in metres;

r

T

is the nominal ty re ra ius, in metres;

F

r0

is the rol ing resistance v alue measured on

drum1, in newtons;

F

r0

is the rol ing resistance v alue measured on

drum2, in newtons

C

r F

r

L

m

=

Annex A (norma tive)

Test equipment tolera nces

A.1 Purpose

The lmits specified in this an ex are neces ary in

order to achiev e suita le lev els of repeata le test

results, which can also be cor elated among v arious

test la oratories These tolerances are not meant to

represent a complete set of eng ine ring

specifications for test eq uipment: instea , they

should serv e as g uid elnes for achiev ing rela le test

results

A.2 Test rims

A.2.1 Width

The test rim width shal be equal to the

stand rd iz d measuring rim I this is not av aia le,

then the next wider rim ma be chosen It should be

noted that a chang e in rim width wi l result in

d iferent test results

A.2.2 Runout

Ru out shal me t the fol owing c iteria:

— ma imum ra ial ru out:0,5mm

— ma imum lateral ru out: 0,5mm

A.3 Alig nm ent

Ang le d ev iations are c itical to the test results

A.3.1 Load ap l cation

The direction of ty re load ing a plcation shal be

kept normal to the test sur ace and shal p s

throug h the whe l centre within

— 1mra for the for e and d eceleration method s;

— 5mrad for the torque and power method s

A.3.2 Ty e al gnment

A.3.2.1 Ca mber a ngle

The plane of the whe l shal be normal to the test

sur ace within2mrad for al methods

A.3.2.2 Slp a ngle

The plane of the ty re shal be p ralel to the

direction of the test sur ace motion within1 mra

for al methods

A.4 Control ac uracy

A.4.1 G eneral ac uracy

Exclusiv e of perturb tions induced b the ty re and

rim non-u iformities, the test equipment shal be

ca a le of checking the test v aria les within the

fol owing l mits:

— ty re loa ing : ±20N

— inflation pres ure: ±3kPa

— sur ace v elocity :

±0,2 km/h for the power, torque and

d eceleration method s,

±0,5km/h for the for e method;

— time:±0,02 s

— ang ular v elocity :±0,2 %

A.4.2 O pt ional compensat ion f r load/spindle

f rc interact ion and load misal gnment

NOT 2 This comp nsaton a plies for the for e method only

Compensation of both loa /spindle for e interaction

( “ cros talk”) and loa misal g nment ma be

ac ompl shed either b record ing the spind le for e

for both forward an rev er e ty re rotation or b

dy namic machine cal bration I spindle for e is

recorded for forward and rev er e directions ( at each

test condition), compensation is achiev ed b

subtracting the “ rev er e” v alue f om the “ forward ”

v alue and div iding the result b two I dy namic

machine cal bration is intend ed , the compensation

terms ma be easi y incorporated in the d ta

reduction

A.5 Instrum entation ac uracy

The instrumentation used for rea out and record ing

of test d ta shal be ac urate within the tolerances

stated below:

— ty re loa :±10N

— inflation pres ure:±1 kPa

— spind le for e:±0,5N

— torq ue input:±0,5N·m

— distance:±1mm

— electrical power:±10W

— temperature:±0,2 °C

— sur ace v elocity :±0,1 km/h ( for al method s)

— time:±0,01 s

— ang ular v elocity :±0,1 %

A.6 Test sur ac roug hnes

The roug hnes , measured lateraly , of the smo th

ste l drum sur ace shal hav e a ma imum

centrel ne av erag e heig ht v alue of6,34m

A.7 Tyre spindle bearing f iction

W hen using the machine read ing as a method for

determining the p rasitic los es, ty re spindle

bearing fiction should be reg ularly v erified as being

suficiently smal as to be considered neg lig ible

( e.g a coastdown f om8 km/ h to0km/h in not les

that5min with a f e ly rotating ty re)

Annex B (informative)

Optional test conditions

B.1 Purpose

The rol ing resistance of a ty re wi l v ary with

v elocity ,loa an inflation pres ure,as wel as other

factor Depending upon the cir umstances of

p rticular ty re a plcations, it can be useful to

d etermine the efect of these ty re-related

p rameter for the ind iv id ual ty re to be tested I

such information is d esired, the options ind icated

inB.2 andB.3 are recommended Unles otherwise

noted , al aspects of the stand rd test conditions

a ply

B.2 Spe d sensitivity

Tests are car ied out at5 km/h, 9 km/ h

and1 0km/ h, in seq uence ( se 5.1.2) A warm-up

period of at least3 min for the fir t v elocity an at

least20min for each suc es iv e v elocity is required

B.3 Lo d and inflation sensitivity

The recommended load s an inflation pres ures are

g iv en in Ta le B.1

A warm-up period of at least 3 min for the fir t

d ta point an at least10min for each suc es iv e

d ta point are required

B.4 Textured sur ac

In cases where a textured drum sur ace is used

instea of a smo th ste l sur ace, this fact shal be

noted in the test report The sur ace texture shal

then be18 4m de p( 80g rit)

Ta le B.1

Annex C (informative)

inertia for drum a nd tyre as embly —

Decelera tion method

C.1 Limitation

The method s presented here should be considered

only as g uidelnes or practical ex mples of methods

used to measure moments of inertia b the

d eceleration method to achiev e rela le test results

C.2 Test drum inertia

C.2.1 Measurement met hod

C.2.1.1 Equipment ne d ed

The ar ang ement shown in Fig ure C.1 requires, in

ad dition to the drum an its ang ular encoder:

— a l g htweig ht puley mou ted on low-fiction

bearing s;

— a weig ht of k own mas , m, in the range5 kg

to10 kg ;

— suita le wire rope an at achments

C.2.1.2 Ex er imenta l a r r a ngement

Se Fig ure C.1

C.2.1.3 Theor y

Applcation of laws of mechanic to the sy stem

shown in Fig ure C.1 lea s to the folowing equation:

N T 3 The ficton torque of pule b aring s,c , can b

neg lected

Tyr lo d as a

pe c ntag e of

m axim um lo d

Tes inflation pr s ur :

s and rdiz d pr s ur ,

m odified:

where

m is the mas , in ki og rams;

I

P

is the puley inertia, in ki og ram metres

sq uared;

r is the puley ra ius, in metres;

R is the drum rad ius, in metres;

I is the drum inertia, in ki og ram metres

sq uared;

C is the f iction torq ue of drum bearing s,

innewton metres;

g

is the earth ’s g rav ity eq ual to9,81 m/ s

2

;

% Ê

D /% t is the ang ular ac eleration or

deceleration

Fig ure C.1 — Arrang em ent