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

BRITISH STANDARD AUTOMOBILE SERIES

BS AU
50-1 .2.3:1 993
ISO 9948:1 992

Tyres and wheels —
Part 1 : Tyres —
Section 2: Commercial vehicle tyres —
Subsection 2.3 Method of measuring
rolling resistance

UD C [62 9 . 1 1 4. 3 /. 5 ] . 0 1 2 . 5 5 : 5 3 1 . 45 . 0 83

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BS AU 5 0-1 .2.3:1 993

Committees responsible for this
British Standard

The preparation of this British Standard was entrusted by the Automobile
Standards Policy Committee (AUE/- ) to Technical Committee AUE/4, upon
which the following bodies were represented:
Agricultural Engineers’ Association
Automobile Association
British Industrial Truck Association
British Pressure Gauge Manufacturers’ Association
British Rubber Manufacturers’ Association
Bus and Coach Council

Department of Transport
Freight Transport Association
Institute of Road Transport Engineers (Inc)
Motor Cycle Industry’s Association of Great Britain Ltd.
Motor Industry Research Association
National Tyre Distributors’ Association
Retread Manufacturers’ Association
Road Haulage Association Ltd.
Society of Motor Manufacturers and Traders Ltd.

This British Standard, having
been prepared under the
direction of the Automobile
Standards Policy Committee,
was published under the
authority of the Standards
Board and comes
into effect on

Amendments issued since publication

1 5 May 1 993
© BSI 1 2- 1 999

The following BSI references
relate to the work on this
standard:
Committee reference AUE/4
Draft for comment 91 /71 575 DC

ISBN 0 5 80 21 747 7

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Amd. No.

Date

Comments


BS AU 5 0-1 .2.3:1 993

Contents

Page
Committees responsible

Inside front cover

National foreword

ii

1

Scope

1

2

Definitions

1

3

Test methods

1

4

Test equipment

1

5

Test conditions

2

6

Test procedure

2

7

Data interpretation

3

8

Data analysis

4

Annex A (normative) Test equipment tolerances

6

Annex B (informative) Optional test conditions

7

Annex C (informative) Measurement methods of moment of
inertia for drum and tyre assembly — Deceleration method

7

Figure 1 — Free- body diagram of tyre/drum system, assuming

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no bearing and windage losses

3

Figure C. 1 — Arrangement

8

Figure C. 2 — Spring method

9

Figure C. 3 — Bifilar pendulum (rope) method

9

Table B. 1

7

i


BS AU 5 0-1 .2.3:1 993

National foreword

This Subsection of this Part of BS AU 50 has been prepared under the direction
of the Automobile Standards Policy Committee. It is identical with
ISO 9948: 1 992

Truck and b us tyres — Metho ds o f m easuring rolling resistance,

published by the International Organization for Standardization (ISO). Other
Parts of this standard are as follows:
—

Part 2: Wheels and rim s;

—

Part 3: Valv es;

—

Part 4: Rim p rofiles and dim ensions.

A British Standard does not purport to include all the necessary provisions of a
contract. Users of British Standards are responsible for their correct application.
Compliance with a British Standard does not of itself confer immunity
from legal obligations.

Summary of pages

This document comprises a front cover, an inside front cover, pages i and ii,
pages 1 to 9 and a back cover.
This standard has been updated (see copyright date) and may have had
amendments incorporated. This will be indicated in the amendment table on the
inside front cover.

ii
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BS AU 5 0 -1 . 2 . 3 : 1 993

2.5

1 S cope

This International Standard specifies methods for

parasitic loss

measuring rolling resistance, under controlled

loss of energy (or energy consumed) per unit

laboratory conditions, for new pneumatic tyres

distance excluding tyre losses, and attributable to

designed primarily for use on trucks and buses. The

aerodynamic loss, bearing friction and other sources

relationship between values obtained and the fuel

of systematic loss which may be inherent in the

economy of the vehicle is undetermined, and such

measurement

values are not intended to be used to indicate levels

2.6

of performance or quality.

skim re ading

This International Standard applies to all truck and

type of parasitic loss measurement, in which the

bus tyres.

tyre is kept rolling, without slippage, while reducing

It enables comparisons to be made between the

the tyre load to a level at which energy loss within

rolling resistance of new tyres when they are

the tyre itself is virtually zero

free- rolling straight ahead, in a position
perpendicular to the drum outer surface, and in
steady- state conditions.
In measuring tyre rolling resistance, it is necessary
to measure small forces in the presence of much
larger forces. It is, therefore, essential that

2.7
machine reading

type of parasitic loss measurement, involving losses
of the test machine, exclusive of losses in the
rotating spindle which carries the tyre and rim

equipment and instrumentation of appropriate

2.8

accuracy be used.

mome nt of ine rtia

(see Annex C)
2 D efinitions

For the purposes of this International Standard, the

3 Test methods

following definitions apply.

The following alternative measurement methods

2.1

are given in this International Standard. The choice

rolling resistance,

F

of an individual method is left to the tester. For each

r

loss of energy (or energy consumed) per unit of
distance
NOTE 1

method, the test measurements shall be converted
to a rolling resistance force acting at the tyre/drum
interface.

The SI unit conventionally used for the rolling

resistance is the newton metre per metre (N·m/m) .
This is equivalent to the drag force in newtons (N) .
2.2
rolling resistance coe fficie nt,

C

r

a) Force method: the reaction force at the tyre
spindle.
b) Torque method: the torque input to the test
drum.

ratio of the rolling resistance, in newtons, to the load

c) Power method: the power input to the test

on the tyre, in newtons. This quantity is

drum.

dimensionless and is derived as follows:

d) Deceleration method: the deceleration of the

C

r

=

rolling resistance
test load

test drum and tyre assembly.
4 Test equipment

2.3
cappe d inflation

process of inflating the tyre and allowing the

4 . 1 D rum spe cifications
4.1 .1

Diameter

inflation pressure to build up, as the tyre is warmed

The test dynamometer shall have a cylindrical

up while running

flywheel (drum) with a diameter of between 1 , 7 m

2.4
regulate d inflation

process of inflating the tyre to the required pressure
independent of its temperature, and maintaining

and 3 m inclusive. It should be noted that the
results are different; see

8. 3

for drum diameter

correction for comparisons, if necessary.
4.1 .2

Surface

this inflation pressure while the tyre runs under

The surface of the drum shall be smooth steel or

load. This is most commonly done by using a

textured, and shall be kept clean. For the textured

regulated pressure source attached to the tyre

drum surface, see

B. 4 .

through a rotating union. (See Annex B. )

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BS AU 5 0 -1 . 2 . 3 : 1 993

4.1 .3

Width

5 . 3 Test inflation p ressure

The width of the drum test surface shall exceed the The inflation pressure shall be the inflation
width or the test tyre tread.
pressure, specified by the tyre manufacturer
concerned, corresponding to the maximum single
tyre load capacity. The inflation pressure shall be
The tyre shall be mounted on a test rim, as specified capped with the accuracy specified in
.
in Annex A.
When the deceleration method is selected, the
following requirements apply:
Measurement of these parameters shall be
a) for duration, %t, the time increments shall not
sufficiently accurate and precise to provide the
exceed 0,5 s;
required test data. The specific and respective
b) any variation of the test drum velocity shall not
values are shown in Annex A.
exceed 1 km/h.
4 . 2 Te st rim

A. 4 . 1

5 . 4 D uration and velocity

4 . 3 Load, alignme nt, control and

instrume ntation accuracies

4 . 4 The rmal e nvironme nt

Reference conditions

5 . 5 O ptional conditions

the sensitivities of load, inflation or velocity
The reference ambient temperature, as measured If
are
desired, the additional information given
on the rotational axis or the tyre, 1 m away from the in Annex
B should be consulted.
plane touching the nearest tyre sidewall, shall
be 25 °C.
Alternative conditions
The test procedure steps described below are to be
If the reference temperature cannot be obtained, the followed in the sequence given.
rolling resistance measurement shall be corrected to
standard temperature conditions in accordance
To ensure repeatability of measurements, an initial
with .
break-in
and cooling period is required prior to the

Drum surface temperature
start or the test. Such a break-in should be carried
Care should be taken to ensure that the
out on a vehicle or on a test drum of at least 1,7 m in
temperature of the test drum surface is
diameter.
approximately the same as the ambient
temperature at the beginning of the test.
Place the inflated tyre in the thermal environment
of the test location for the time necessary to achieve
thermal
equilibrium which is generally reached
The test consists of a measurement of rolling
after
6
h.
resistance in which the tyre is inflated and the
inflation pressure allowed to build
up (i.e., “capped air”).
After thermal conditioning, the inflation pressure
shall be adjusted to the test pressure and
verified 10 min after the adjustment was made.
Test speed for load index 122 and above
The value shall be obtained at a drum speed
The tyre shall be run at constant test velocity until
of 80 km/h for tyres with speed symbols K to M
inclusive and at 60 km/h for speed symbols F to J reaching a stabilized steady-state value of rolling
resistance. Recommendations for warm-up periods
inclusive.
are given in Annex B.

Test speeds for load index 121 and below
The values shall be obtained at drum speeds
The following shall be measured and recorded
of 80 km/h, and if required, 120 km/h.
(see Figure 1):
a) test velocity, Un;
The standard test load shall be computed from 85 %
b) load on the tyre normal to the drum surface,
of the maximum single load capacity of the tyre
Lm ;
and shall be kept within the tolerance specified
c) test inflation pressure:
in Annex A.
1) initial, as defined in ,
2) final, for capped inflation;
4.4.1

6 Test procedure

4.4.2

6. 1 Break-in

8. 2

4.4.3

6. 2 Thermal conditioning

5 Test conditions

6. 3 Pressure adj ustme nt

5 . 1 Te st spe eds
5.1 .1

6. 4 Warm-up

5.1 .2

6. 5 Me asure me nt and re cording

5 . 2 Test load

6. 3

2

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BS AU 5 0 -1 . 2 . 3 : 1 993

T , the
F , the input power, V × A, or

d) the driving torque on the drive shaft,
tyre spindle force,

t

t

the deceleration of the test drum/tyre/wheel

%Ê/%t, depending on the method;
);
r (see
;
f) ambient temperature, t
g) test drum radius, R;

assembly,

e) distance,

7. 2 . 1

L

amb

h) test method chosen;
i) test rim (designation and material) .
6. 6 Me asure ment of p arasitic losse s

Determine parasitic losses by a procedure given
in

6. 6. 1 , 6. 6. 2

6. 6. 1

or

6. 6. 3 .

Skim reading

a) Reduce the load to maintain the tyre at the test
velocity without slippage to, for example, 50 N.
b) Record the spindle force,

F

p

input torque,

T , or
p

the power, whichever applies.
c) Record the load on the tyre normal to the drum
surface,
6. 6. 2

L.

p

Machine reading

a) Remove the tyre from the test drum surface.

U , record the input torque,
T , the power, or the test drum deceleration,

b) At the test velocity,

n

p

whichever applies.
6. 6. 3

Deceleration method

Figure 1 — Fre e -b ody diagram of tyre /drum
system, assuming no b e aring and windage

a) Remove the tyre from the test drum surface.
b) Record the deceleration of the test

%Ê /%t, and that of the unloaded
tyre, %Ê /%t .

drum,

o

po

losse s

Parasitic losses

7. 1 . 3

Calculate the parasitic losses,

F , in newtons, as
p

7 D ata interpretation
7. 1 Sub traction of p arasitic losse s

The parasitic losses shall be subtracted as shown
in

7. 1 . 1 , 7. 1 . 2

7.1 .1

or

7. 1 . 3 .

Skim reading

Subtract the skim reading from the test
measurement.
7.1 .2

Machine reading

Subtract the machine reading from the test

where

I

is the test drum inertia in rotation, in

D

R
Ê

kilogram metres squared;
is the test drum surface radius, in metres;
vo

%t

is the test drum angular velocity, without
tyre, in radians per second;

o

is the time increment chosen for the
measurement of the parasitic losses

measurement.

without tyre, in seconds;

I

T

R
Ê

is the tyre and wheel inertia in rotation, in
kilogram metres squared;

r

is the tyre rolling radius, in metres;

po

is the tyre angular velocity, unloaded tyre,
in radians per second.

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BS AU 5 0-1 .2.3:1 993

Ê

7.2 Rolling resistance calculation

The net values of driving torque, spindle force,

F , expressed in newtons, using the

Force method

The rolling resistance,

R
M
F

t

method.

is the distance from the tyre axis to the drum

L

R

8 Data analysis

outer surface under steady- state conditions,

8.1 Rolling resistance coefficient

in metres;

The rolling resistance coefficient,

is the test drum radius, in metres.

dividing the rolling resistance by the load on the

Torque method

7.2.2

The rolling distance,

F , in newtons, is calculated

Cr

r

T
R

F
L

where

T
R

is the input torque, in newton metres;
is the test drum radius, in metres.

Power method

7.2.3

The rolling resistance,

=

r

F , in newtons, is calculated
r

drive, in amperes;
is the test drum velocity, in kilometres per
hour.

Deceleration method

The rolling resistance,

is the test load, in newtons.

are unavoidable (only temperatures not less
than 20 ° C nor more than 30 ° C are acceptable) ,

r25

is the electric current drawn by the machine

7.2.4

m

8.2 Temperature correction

F

machine drive, in volts;

n

is the rolling resistance, in newtons;

F

r25

is the

rolling resistance at 25 ° C, in newtons:

is the electrical potential applied to the

U

r

using the following equation, where

where

A

m

then a correction for temperature shall be made

V× A
U

3, 6

n

V

Fr

L

=

If measurements at temperatures other than 25 ° C

with the equation

F

r

where

= ----

r

C , is calculated by

tyre:

with the equation

F

is as defined in 7.1 .3 .

measure the moments of inertia for the deceleration

is the tyre spindle force, in newtons;

t

P

is the tyre aerodynamic torque;

Annex C gives guidelines and practical examples to

L

where

F
r

is the tyre rolling radius, in metres;

AP

r

F = F [1 + (r /R) ]
r

kilogram metres squared;

r

F , in newtons, is calculated

with the equation

is the tyre and wheel inertia in rotation, in

T

r

appropriate method, as shown in 7.2.1 to 7.2.4 .
7.2.1

tyre, in radians per second;

I

power or deceleration are to be converted to rolling
resistance,

is the test drum angular velocity, loaded

v

F , in newtons, is calculated
r

with the equation

=

F [1 + K(t
r

amb

– 25)]

where

F
t

r

amb

K

is the rolling resistance, in newtons;
is the ambient temperature, in degrees
Celsius;
is equal to
0, 006 for truck and bus tyres with load
index 1 22 and above,
0, 01 for truck and bus tyres with load
index 1 21 and lower.

where

I

is the test drum inertia in rotation, in

D

R
%t

kilogram metres squared;
is the test drum surface radius, in metres;
v

is the time increment chosen for the
measurement, in seconds;

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BS AU 5 0-1 .2.3:1 993

8.3 Drum diameter correction
Test res ults ob tained from different drum diameters
may b e comp ared b y us ing the following theoretical
formula:

F Ò KF

02

r0 1

with

where

R
R
r
F

1

2

T

r0 1

F

r0 2

is the radius of drum 1 , in metres ;
is the radius of drum 2 , in metres ;
is the nominal tyre radius , in metres ;
is the rolling res is tance value measured on
drum 1 , in newtons ;

is the rolling res is tance value measured on
drum 2 , in newtons .

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BS AU 50-1 .2.3:1 993

Annex A (normative)
Test equipment tolerances

A.4 Control accuracy
A.4.1 General accuracy

Exclusive of perturbations induced by the tyre and
rim non-uniformities, the test equipment shall be
The limits specified in this annex are necessary in capable of checking the test variables within the
order to achieve suitable levels of repeatable test
following limits:
results, which can also be correlated among various
— tyre loading: ± 20 N
test laboratories. These tolerances are not meant to
— inflation pressure: ± 3 kPa
represent a complete set of engineering
— surface velocity:
specifications for test equipment: instead, they
should serve as guidelines for achieving reliable test

± 0,2 km/h for the power, torque and
results.
deceleration methods,
A.2 Test rims
± 0,5 km/h for the force method;
A.2.1 Width
— time: ± 0,02 s
The test rim width shall be equal to the
— angular velocity: ± 0,2 %
standardized measuring rim. If this is not available, A.4.2 Optional compensation for load/spindle
then the next wider rim may be chosen. It should be force interaction and load misalignment
noted that a change in rim width will result in
NOTE 2 This compensation applies for the force method only.
different test results.
Compensation of both load/spindle force interaction
A.2.2 Runout
(“crosstalk”) and load misalignment may be
Runout shall meet the following criteria:
accomplished either by recording the spindle force
for both forward and reverse tyre rotation or by
— maximum radial runout: 0,5 mm
dynamic
machine calibration. If spindle force is
— maximum lateral runout: 0,5 mm
recorded
for forward and reverse directions (at each
A.3 Alignment
test condition), compensation is achieved by
Angle deviations are critical to the test results.
subtracting the “reverse” value from the “forward”

value and dividing the result by two. If dynamic
A.3.1 Load application
machine calibration is intended, the compensation
The direction of tyre loading application shall be
terms may be easily incorporated in the data
kept normal to the test surface and shall pass
reduction.
through the wheel centre within
— 1 mrad for the force and deceleration methods; A.5 Instrumentation accuracy
The instrumentation used for readout and recording
— 5 mrad for the torque and power methods.
of
test data shall be accurate within the tolerances
A.3.2 Tyre alignment
stated below:
A.3.2.1 Camber angle
— tyre load: ± 10 N
The plane of the tyre shall be normal to the test
— inflation pressure: ± 1 kPa
surface within 2 mrad for all methods.
— spindle force: ± 0,5 N
A.3.2.2 Slip angle
—
torque input: ± 0,5 N·m
The plane of the tyre shall be parallel to the
— distance: ± 1 mm
direction of the test surface motion within 1 mrad
— electrical power: ± 10 W
for all methods.
— temperature: ± 0,2 °C

— surface velocity: ± 0,1 km/h (for all methods)
— time: ± 0,01 s
— angular velocity: ± 0,1 %
A.1 Purpose

6

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BS AU 50-1 .2.3:1 993

A.6 Test surface roughness
The roughness, measured laterally, of the
smooth steel drum surface shall have a maximum
centre- line average height value of 6, 3

4m.

Annex C (informative)
Measurement methods of moment
of inertia for drum and tyre
assembly — Deceleration method

A.7 Tyre spindle bearing friction
When using the machine reading as a method for

C.1 Limitation

determining the parasitic losses, tyre spindle

The methods presented here should be considered

bearing friction should be regularly verified as being

only as guidelines or practical examples of methods

sufficiently small as to be considered negligible

used to measure moments of inertia by the

(e. g. , a coastdown from 80 km/h to 0 km/h in not

deceleration method to achieve reliable test results.

less than 5 min with a freely rotating tyre) .

C.2 Test drum inertia

Annex B (informative)
Optional test conditions

C.2.1

Measurement method

C.2.1 .1

Equipment needed

The arrangement shown in Figure C. 1 requires, in
addition to the drum and its angular encoder:

B.1 Purpose
The rolling resistance of a tyre will vary with

— a lightweight pulley mounted on low- friction

velocity, load and inflation pressure, as well as other

bearings;

factors. Depending upon the circumstances of

— a weight of known mass,

particular tyre applications, it can be useful to

to 1 00 kg;

determine the effect of these tyre- related
parameters for the individual tyre to be tested. If
such information is desired, the options indicated

— suitable wire rope and attachments.

C.2.1 .2

Experimental arrangement

in B.2 and B.3 are recommended. Unless otherwise

See Figure C. 1 .

noted, all aspects of the standard test conditions

C.2.1 .3

apply.

m , in the range 50 kg

Theory

Application of laws or mechanics to the system

B.2 Speed sensitivity

shown in Figure C. 1 leads to the following equation:

A warm- up period of at least 90 min for capped
pressure conditions, and at least 30 min for
regulated pressure conditions is required.

B.3 Load and inflation sensitivity
If load and inflation sensitivity is required, test in
accordance with Table B. 1 , in a sequence which
results in steadily decreasing values of rolling

resistance. For most tyres, the sequence shown
accomplishes this obj ective.
A warm- up period of at least 90 min for the first
data point and at least 30 min for each successive
data point is required.

In cases where a textured drum surface is used
instead of a smooth steel surface, this fact shall be
noted in the test report. The surface texture shall

4m deep (80 grit).

Table B.1
Tyre load as a percentage

Inflation pressure as a

of maximum load

percentage of rated pressure

1 00
1 00

is the pulley inertia, in kilogram metres

P

squared;

r
R
I

is the pulley radius, in metres;
is the drum radius, in metres;
is the drum inertia, in kilogram metres

D

squared;
is the friction torque of drum bearings, in
newton metres;

g

%Ê
%t

is the earth’s gravity equal to 9, 81 m/s 2 ;
D/

NOTE 3
neglected.

is the angular acceleration or deceleration
of the drum, in radians per second squared.
The friction torque of pulley bearings,

c, can be

95 regulated
70 regulated

50

1 20 regulated

25

70 regulated

© BSI 1 2- 1 999

is the mass, in kilograms;

1 00 capped

75

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m
I

C

B.4 Textured surface

then be 1 80

where

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BS AU 5 0-1 .2.3:1 993

Theory

C.3.1 .2

Equation of free movement of pendulum, if

Ú is the

angle from equilibrium:

I

0

Ú + KÚ = 0

d2
d

t

2

Natural oscillation period,

T:
0

where

Ú

is the angle of oscillation, in radians;

t
I

is the torsion pendulum inertia, in kilogram

K

is the spring constant.

is the period of time, in seconds;

0

square metres;

C.3.1 .3
Figure C .1 — Arrangement
C.2.1 .4

Method

Method

Measurement of oscillation periods, with the tyre
assembly,

m, is released, the angular

When the mass,

acceleration is measured through the angular

T

1

and without,

tyre assembly inertia,

I

T

=

K T

4

encoder fitted to the drum axle (and otherwise used

;

2

(

2
1

–

T

2
0

I:

T , call be used to give the
o

T

)

Bifilar pendulum (rope) method

to measure drum decelerations).

C.3.2

The friction torque,

Tyre inertia can be obtained by the period time of

C, of drum bearings can also be

measured, provided that the rope can be separated

twisted oscillation of a tyre hanging from two steel

from the drum once mass,

ropes of exactly the same length (see Figure C. 3) .

m , has given sufficient

momentum to the drum, for the subsequent drum
deceleration is directly related to

%Ê
I  % t

D

D

 dec

=

C by:

C

C.3.2.1

Theory

The tyre inertia,

I , in kilograms metres squared, is
T

determined by

where the values are as defined in C .2.1 .3 .
C.2.2

Determination method

The drum inertia is estimated by calculation.
The drum inertia,

I , in kilogram metres squared, is
D

determined by the summation of the inertia of each
drum part (flange, disc, reinforced rib):

I

D

=

I +I +I
f

d

f

is the drum flange inertia;

d

is the drum disc inertia;

r

is the reinforced rib inertia;

all values being expressed in kilogram metres
squared.

W
a
h

is the oscillation period, in seconds;
is the tyre and wheel weight, in newtons;
is the distance between point A and B, in
metres;
is the distance between points C and D, in
metres;
is the vertical distance between lines AB
and CD, in metres.

C.3.2.2

Method

The time period,

E, or the twisted oscillation of a tyre

is measured, and tyre inertia can be calculated from

C.3 Tyre assembly inertia
C.3.1

E

b

r

where

I
I
I

where

the equation given in C.3.2.1 .

Spring method

C.3.1 .1

Equipment needed

Torsion pendulum of inertia

K (see Figure C. 2).
8

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I

0

and spring constant

© BSI 1 2- 1 999


BS AU 50-1 .2.3:1 993

Figure C.2 — Spring method

Figure C.3 — Bifilar pendulum
(rope) method

© BSI 1 2 - 1 999
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9


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