BRITISH STANDARD

BS AU
50-1 -4.4b:1 992
ISO 425 1 -5 :
1 992

Tyres and wheels —
Part 1 : Tyres —
Section 4: Agricultural tractor and
machine tyres —
Subsection 4.4b: Specification for ply
rating marked series tyres for log
skidders

IC S 65 . 0 60 . 0 1 ; 83 . 1 60 . 3 0

Incorporating
Amendment No. 1 to
BS AU 50-1 -4. 4a:1 992
(Renumbers the BS as
BS AU 50-1-4. 4b:
1992), not published
separately


BS AU 5 0-1 -4.4b:1 992

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.
Royal Automobile Club
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
1 5 October 1 992


Amendments issued since publication

© BSI 03- 2000

Amd. No.

Date

Comments

The following BSI references

1 0363

May 1 999

Indicated by a sideline in the margin

relate to the work on this
standard:
Committee reference AUE/4
Draft for comment 90/82455 DC

ISBN 0 5 80 21 2 1 1 4


BS AU 5 0-1 -4.4b:1 992

Contents


Page
Committees responsible

Inside front cover

National foreword

ii

1

Scope

1

2

Normative references

1

3

Definitions

1

4

Marking


1

5

Dimensions and tolerances

1

6

Tyre load ratings

1

7

Rims

2

8

Tubes

2

Table 1 — Tyre sizes, rim width codes and dimensions

1


Table 2 — Basic tyre loads (BTL) and corresponding inflation
pressures (IP)
Table 3 — Tyre loads at different speeds (load- speed relationship)

2

Table 4 — Approved rim contours

2

List of references

© BSI 03- 2000

2

Inside back cover

i


BS AU 5 0-1 -4.4b:1 992

National foreword

This Subsection of this Part of BS AU 50, prepared under the direction of the
Automobile Standards Policy Committee, is identical with ISO 4251 - 5: 1 992

Tyres (ply rating marked series) and rims for agricultural tractors and

machines — Part 5: Log skidder tyres , published by the International
Organization for Standardization (ISO). This edition supersedes
BS AU 50- 1 - 4. 4a: 1 992, which is withdrawn.
BS AU 50 is issued in four Parts:
—

Part 1: Tyres;

—

Part 2: Wheels and rims;

—

Part 3: Valves;

—

Part 4: Rim profiles and dimensions.

ISO 4251 cover requirements for tyres and rims for agricultural tractors and
machines. Other Parts of ISO 4251 have been implemented as British Standards
as Subsections of BS AU 50 as follows:
ISO 425 1

BS AU 5 0

Part 1 :

Tyre designations and dimensions


Part 1 : Subsection 4. 1

Part 2:

Tyre load ratings

Part 1 : Subsection 4. 2

Part 3:

Rims

Part 4: Subsection 4. 1

Part 4:

Tyre classification and nomenclature

Part 1 : Subsection 4. 3

Cross-references

The Technical Committee has reviewed the provisions of ISO 4223- 1 to which
normative reference is made in the text and has decided that they are acceptable
for use in conj uction with this standard.
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 and 2, an inside back cover 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

© BSI 03- 2000


BS AU 5 0 -1 -4 . 4 b: 1 992

3.1

1 S cope

This part of ISO 4251 sets out the designation,
dimensions, load ratings and rim coordination of ply special design agricultural tyre suitable for forestry
rating marked series of log skidder tyres of diagonal application
construction.
Rim dimensions are given in ISO 4251-3.
maximum load of total vehicle mass with
accessories plus load increases due to log winching
The following standards contain provisions which, or grappling loads and mass transfer that is
through reference in this text, constitute provisions imposed on an individual tyre due to total radial
of this part of ISO 4251. At the time of publication, forces during operation

the editions indicated were valid. All standards are
subject to revision, and parties to agreements based
on this part of ISO 4251 are encouraged to
The marking of ply rating marked series of tyres for
investigate the possibility of applying the most
log skidders shall consist of designations of the tyre
recent editions of the standards indicated below.
size and ply rating and the distinctive marking LS;
Members of IEC and ISO maintain registers of
additional information shall be as specified in
currently valid International Standards.
ISO 4251-1.
ISO 4223-1:1989, Definitions of some terms used in
logging se rvice tyre

3.2

b asic tyre load for log skidde rs

2 Normative references

4 Marking

the tyre industry — Part 1: Pneumatic tyres.

ISO 4251-1:1992, Tyres (ply rating marked series)

and rims for agricultural tractors and
machines — Part 1: Tyre designation and
dimensions.


ISO 4251-3:1985,

Tyres and rims (existing series) for
agricultural tractors and machines — Part 3: Rims.

5 D imensions and tolerances

Standard sizes, measurement rims, design
dimensions of new, diagonal construction log
skidder tyres, of both normal and low section height,
and maximum tyre dimensions in service shall be as
given in Table 1.
6 Tyre load ratings

3 D efinitions

For the purposes of this part of ISO 4251, the
definitions given in ISO 4223-1 and the following
definitions apply.

Basic tyre loads for log skidder tyres of diagonal
construction, and normal and low section height, for
a maximum speed of 30 km/h are given in Table 2.
The loads given are maximum values and are valid
for the inflation pressures indicated.

6. 1

Tab le 1 — Tyre siz es, rim width code s and dimensions


Dimensions in millimetres
D e sign ne w tyre
Tyre siz e

Me asure me nt rim

de signation

w id th cod e

18.4 – 26 LS
18.4 – 34 LS
23.1 – 26 LS
24.5 – 32 LS

16
16
20
21

28 L – 26 LS
25
30.5 L – 32 LS 27

S e ctio n width

467
467
587

622
714
775

O ve rall diame te r

Normal se ction he ight tyre s

1 476
1 679
1 632
1 831

Low se ction he ight tyre s

1 644
1 847

In se rvice

b

a

Maximum o ve rall

Maximum ove rall

width


diame te r

504
504
634
672

1 525
1 728
1 691
1 892

771
837

1 703
1 909

a Skidder manufacturers should recognize that specialized tyres with deeper tread and corresponding increased overall diameter

may be used.

b Minimum new tyre overall diameter is calculated on the basis of a tolerance of – 3 % on design section height.

© BSI 03-2000

1


BS AU 50-1 -4.4b:1 992


Table 2 — Basic tyre loads (BTL) and corresponding inflation pressures (IP)
1 0 PR
Tyre size designation

18.4 – 26 LS
18.4 – 34 LS
23.1 – 26 LS
24.5 – 32 LS

BTL

1 2 PR
IP

kg

BTL

kPa

2 580
2 920
3 250

170
170
140

kg


1 4 PR
IP

BTL

kPa

3 250

210

4 495

170

Table 3 — Tyre loads at different speeds
(load-speed relationship)

15
25
30
40

BTL

kPa

IP


kg

kPa

Normal section height tyres

28 L – 26 LS
3 760
30.5 L – 32 LS
4 710
6.2 For logging operations with a maximum speed
of 8 km/h, tyre loads may be increased to 110 % of
the values given in Table 2 with no increase in
inflation pressure.
6.3 For transport service and operations which do
not require sustained high torque, the loads at
various speeds given in Table 3 apply with no
change in inflation pressure.
km/h

IP

kg

Low section height tyres

Maximum speed

1 6 PR


Maximum tyre load

a

120
110
100
90

a Expressed as a percentage of the basic tyre loads given

in Table 2.

140
140

3 720

260

4 285

170

5 370

170

8 Tubes


Whenever an inner tube is required, it shall be
identified by the same designation as the size of the
tyre in which it is to be mounted.
Table 4 — Approved rim contours
Tyre size

Measurement rim

Approved rim

designation

width code

contours

18.4 – 26 LS
18.4 – 34 LS
23.1 – 26 LS
24.5 – 32 LS

Normal section height tyres

16
16
20
21

DW 16 A
DW 16 A

DW 20 A
DW 21 A
DH 21

Low section height tyres

28 L – 26 LS 25
30.5 L – 32 LS 27

DW 25 A
DW 27 A
DH 27

7 Rims
7.1 Rim contours

See ISO 4251-3.

7.2 Rim coordination

In addition to the measurement rim width given
in Table 1, the approved rim contours are given
in Table 4 for tyres for log skidders with normal and
low section height.
Consult rim and wheel manufacturer for
confirmation of the strength of rim/wheel for the
intended service.

2


© BSI 03-2000


BS AU 5 0-1 -4.4b:1 992

List of references

See national foreword.

© BSI 03- 2 000


BS AU
5 0-1 -4.4b:1 992
ISO 425 1 -5 :

BSI — British Standards Institution

1 992
BS I is the indep endent national b ody res p ons ib le for p rep aring
Britis h S tandards . It p res ents the UK view on s tandards in E urop e and at the
international level. It is incorp orated b y Royal C harter.

Revisions
Britis h S tandards are up dated b y amendment or revis ion. Us ers of
Britis h S tandards should make s ure that they p oss es s the latest amendments or
editions .

It is the constant aim of BS I to imp rove the quality of our p roducts and services .
We would b e grateful if anyone finding an inaccuracy or amb iguity while us ing

this Britis h S tandard would inform the S ecretary of the technical committee
res p ons ib le, the identity of which can b e found on the inside front cover.
Tel: 02 0 89 96 90 00. Fax: 02 0 89 96 7 40 0 .

BS I offers memb ers an individual up dating s ervice called PLUS which ens ures
that s ub s crib ers automatically receive the lates t editions of s tandards .

Buying standards
O rders for all BS I, international and foreign s tandards p ub lications s hould b e
addres s ed to C us tomer S ervices. Tel: 0 2 0 899 6 9 00 1 . Fax: 0 2 0 899 6 7001 .

In res p ons e to orders for international standards , it is BS I p olicy to sup p ly the
BS I imp lementation of thos e that have b een p ub lis hed as Britis h S tandards,
unless otherwis e requested.

Information on standards
BS I p rovides a wide range of information on national, E urop ean and
international standards through its Lib rary and its Technical H elp to E xp orters
S ervice. Various BS I electronic information s ervices are also availab le which give
details on all its p roducts and s ervices . C ontact the Information C entre.
Tel: 02 0 89 96 71 1 1 . Fax: 02 0 89 96 7 048.

S ub s crib ing memb ers of BS I are kep t up to date with s tandards develop ments
and receive sub s tantial discounts on the p urchase p rice of s tandards. For details
of thes e and other b enefits contact Memb ership Adminis tration.
Tel: 02 0 89 96 70 02 . Fax: 02 0 89 96 7 00 1 .

Copyright
C op yright s ub s is ts in all BS I p ub lications . BS I als o holds the cop yright, in the
UK, of the p ub lications of the international s tandardization b odies . E xcep t as

p ermitted under the C op yright, D es igns and Patents Act 1 988 no extract may b e
rep roduced, s tored in a retrieval s ystem or transmitted in any form or b y any
means – electronic, p hotocop ying, recording or otherwis e – without p rior written
p ermis s ion from BS I.

This does not p reclude the free us e, in the cours e of imp lementing the standard,
of necess ary details such as s ymb ols, and size, typ e or grade designations. If thes e
details are to b e used for any other p urp os e than imp lementation then the p rior
written p ermiss ion of BS I must b e ob tained.

If p ermis sion is granted, the terms may include royalty p ayments or a licensing
agreement. D etails and advice can b e ob tained from the C op yright Manager.
BS I
3 89 C his wick H igh Road
London
W4 4AL

Tel: 02 0 89 96 70 7 0.