Bsi bs au 050 1 2 3 1993 (1999) iso 9948 1992

BRITISH STANDARD AUTOMOBILE SERIES BS AU 50 1 2 3 1993 ISO 9948 1992 Tyres and wheels — Part 1 Tyres — Section 2 Commercial vehicle tyres — Subsection 2 3 Method of measuring rolling resistance UDC [6[.]

ISO 9948:1992

U C[ 62 1 4.3 5]0 2.5 :5 1.4 0 3

This Bri sh Stan 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 rdan comes

into fecton

1 Ma 1 9

© BSI1 -1 9

The folowing BSI references

relate to the work on this

stan ard:

Commi e reference AUE/4

Draft for comment9 / 71 7 DC

ISBN 0 5 0 2 7 7 7

The prep ration of this British Stand 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 methods of moment of

inertia for d rum and ty re as embly — Deceleration method 7

Fig ure 1 — Fre -bod diag ram of ty re/ d rum sy stem, as uming

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 It is identical with

ISO9 4 :19 2 Tr uck a nd bus 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 to9 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 primariy for use on trucks and buses.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 truck and

bus 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 slp ag e, whi e reducing

the ty re load to a lev el at which energ y los within

the ty re itself is v irtual y 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 folowing 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 ty re

spindle

b) Torque 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 n1,7m

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, and shal be kept clean For the textured

d rum 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 or the test ty re trea

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 or the ty re,1m 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 bui d

up( i.e “ a pedair”)

5.1 Test spe ds

5.1.1 Te t spe d f r load index12 and ab ve

The v alue shal be obtained at a d rum spe d

of8 km/h for ty res with spe d sy mbols K to M

inclusiv e an at6 km/ h for spe d sy mbols F to J

inclusiv e

5.1.2 Te t spe ds f r load index121 and below

The v alues shal be obtained at drum spe ds

of8 km/h, an if required,1 0km/h

5.2 Test lo d

The stand ard test loa shal be computed f om8 %

of the ma imum sing le loa ca acity of the ty re

andshal be kept within the tolerance specified

inAnnex 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 sing le

ty re loa ca acity The inflation pres ure shal be

ca ped with the ac uracy specified in A.4.1

5.4 Duration and velocity

W hen the deceleration method is selected , the

fol owing req uirements 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

aredesired , the ad ditional information g iv en

inAnnex B should be consulted

6 Test procedure

The test procedure steps d es ribed below are to be

fol owed in the seq uence g iv en

6.1 Break- n

To ensure repeata i ity of measurements, an initial

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

start or the test S ch a break-n should be car ied

out on a v ehicle or on a test d rum of at least1,7m in

d iameter

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

after6h

6.3 Pres ure a justm ent

After thermal conditioning , the inflation pres ure

shal be a justed to the test pres ure an

v erified10min after the a justment was ma 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 Measurement 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 defined 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 a procedure g iv en

in6.6.1, 6.6.2 or6.6.3

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 spind le 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 drum

sur ace, L

p

6.6.2 Machine reading

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

b) At the test v elocity , U

n , record the input torq ue,

T

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

whichev er a ples

6.6.3 De eleration met hod

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

b) Record the deceleration of the test

drum, % Ê

o /%t, an that of the u loa ed

ty re, % Ê

po /% t

7 Data 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

S btract the skim read ing f om the test

measurement

7.1.2 Machine reading

S btract the machine rea ing f om the test

measurement

7.1.3 Parasit ic los e

Calculate the p rasitic los es, F

p , in newtons, as

Fig ure 1 — Fre - body diag ram of tyre/drum

system , as um ing no bearing and windag e

los es

where

I is the test drum inertia in rotation, in

kiogram metres sq uared ;

R is the test drum sur ace rad ius, in metres;

Ê

vo

is the test drum ang ular v elocity , without

ty re, in rad 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 an whe l inertia in rotation, in

kiogram 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 load ed ty re,

in ra ians per second

7.2 Rol ing resistanc calculation

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

power or deceleration are to be conv erted to rol ing

resistance, F

r , ex res ed in newtons, using the

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

7.2.1 Fo c met hod

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 ing distance, F

r , in newtons, is calculated

with the equation

7.2.3 Power met hod

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 nor 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)]

where

F

t

is the ty re spindle for e, in newtons;

r

L

is the d istance 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 d rawn b the machine

d riv e, in amperes;

U

n

is the test d rum v elocity , in kiometres per

hour

where

I is the test drum inertia in rotation, in

ki og ram metres sq uared;

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

%t

v

is the time inc ement chosen for the

measurement, in second s;

F

r

T

R

-=

F

r

3,6V×A

U

n

=

Ê

v

is the test d rum ang ular v elocity , loa 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 ng rad ius, in metres;

M

AP

is the ty re aerody namic torq ue;

F

P

is as defined in7.1.3

where

F

r

is the rol ng 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 eq ual to

0,0 6 for truck an bus ty res with load

ind ex1 2 an a ov e,

0,01 for truck and bus ty res with load

ind ex1 1 and lower

C

r F

r

L

m

=

8.3 Drum diameter cor e tion

Test results obtained fom d iferent drum d iameter

ma be comp red b using the folowing the retical

formula:

F

0

ÒKF

r0

with

where

R

1

is the ra ius of drum1, in metres;

R

2

is the ra ius of drum2, 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

Annex A (normative)

Test equipment tolerances

A.1 Purpose

The l mits specified in this annex 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 el nes for achiev ing rel a le test

results

A.2 Test rims

A.2.1 Width

The test rim wid th shal be eq ual 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 result in

diferent test results

A.2.2 Runout

Ru out shal me t the folowing c iteria:

— ma imum rad 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 appl cat ion

The direction of ty re load ing a pl cation shal be

kept normal to the test surace and shal p s

throug h the whe l centre within

— 1 mrad for the for e and d eceleration methods;

— 5mra 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 ty re shal be normal to the test

surace within2 mrad for al methods

A.3.2.2 Slp a ngle

The plane of the ty re shal be p ral el to the

direction of the test surace motion within1mra

for al methods

A.4 Control ac uracy

A.4.1 G eneral ac uracy

Exclusiv e of perturb tions ind uced 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 lmits:

— ty re loa ing :±20N

— inflation pres ure:±3kPa

— sur ace v elocity :

±0,2km/h for the power, torq ue and

deceleration method s,

±0,5km/h for the for e method;

— time: ±0,02s

— ang ular v elocity : ±0,2%

A.4.2 O ptional compensation f r load/spindle

f rc interact ion and load misal gnment

N T 2 This comp nsaton a plies for the fore method only

Compensation of both loa /spind le for e interaction

( “ cros talk”) and loa misalg nment ma be

ac omplshed either b record ing the spindle for e

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

d y namic machine calbration I spindle for e is

record ed for forward and rev er e directions ( at each

test condition), compensation is achiev ed b

subtracting the “ rev er e” v alue fom the “ forward ”

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

machine calbration is intend ed, the compensation

terms ma be easiy incorporated in the d ta

red uction

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:±1kPa

— spind le for e:±0,5N

— torque input: ±0,5N·m

— d istance: ±1 mm

— electrical power:±10W

— temperature:±0,2 °C

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

— time: ±0,01s

— ang ular v elocity : ±0,1%