ISO 9815:2024

International
Standard
ISO 9815
Fourth edition
Road vehicles — Passenger-car
2024-09
and trailer combinations — Lateral
stability test
Véhicules routiers — Ensembles voiture particulière et remorque
— Essai de stabilité latérale
Reference number
© ISO 2024
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms, definitions . 1
4 Measurement variables . 2
5 General conditions . 2
5.1 Conformity .2
5.2 Measuring equipment .2
5.3 Test track .2
5.4 Wind velocity .3
5.5 Loading conditions.3
5.5.1 Towing vehicle .3
5.5.2 Trailer .3
5.5.3 Static load on the coupling ball .3
5.5.4 Adjustment of load-distributing coupling mechanisms .4
6 Test method . 5
6.1 General .5
6.2 Test runs .5
6.2.1 Speed .5
6.2.2 Steering impulse .5
6.2.3 Number of test runs .7
7 Data analysis . 7
7.1 General .7
7.2 Individual test runs .8
7.2.1 Effective longitudinal vehicle acceleration .8
7.2.2 Test speed .8
7.2.3 Damping the oscillation of the articulation angle .8
7.2.4 Yaw velocity ratio .9
7.3 Zero-damping speed . .10
7.4 Reference-damping speed .10
7.5 Reference-speed damping .10
8 Data presentation . 10
8.1 General data .10
8.2 Test conditions .10
8.3 Results . .11
Annex A (normative) Test report — General data (supplement to ISO 15037-1:2019, Annex A) .12
Annex B (normative) Test results .15
Annex C (informative) Steady-state behaviour .16
Bibliography . 17

iii
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out through
ISO technical committees. Each member body interested in a subject for which a technical committee
has been established has the right to be represented on that committee. International organizations,
governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely
with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are described
in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the different types
of ISO document should be noted. This document was drafted in accordance with the editorial rules of the
ISO/IEC Directives, Part 2 (see www.iso.org/directives).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent
rights in respect thereof. As of the date of publication of this document, ISO had not received notice of (a)
patent(s) which may be required to implement this document. However, implementers are cautioned that
this may not represent the latest information, which may be obtained from the patent database available at
www.iso.org/patents. ISO shall not be held responsible for identifying any or all such patent rights.
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and expressions
related to conformity assessment, as well as information about ISO's adherence to the World Trade
Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www.iso.org/iso/foreword.html.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.
This document was prepared by Technical Committee ISO/TC 22, Road vehicles, Subcommittee SC 33, Vehicle
dynamics, chassis components and driving automation systems testing.
This fourth edition cancels and replaces the third edition (ISO 9815:2010), which has been technically
revised.
The main changes are as follows:
— additions have been made to 6.2.1, 6.2.2 and 6.2.3;
— additions have been made to 7.2.1, 7.2.2, 7.2.3 and 7.2.4;
— references have been updated to ISO 4138:2021 and ISO 15037-1:2019.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.

iv
Introduction
The main purpose of this document is to provide repeatable and discriminatory test results.
The dynamic behaviour of a road vehicle is a very important aspect of active vehicle safety. Any given vehicle,
together with its driver and the prevailing environment, constitutes a closed-loop system that is unique. The
task of evaluating the dynamic behaviour is therefore very difficult since the significant interaction of these
driver-vehicle-environment elements are each complex in themselves. A complete and accurate description
of the behaviour of the road vehicle must necessarily involve information obtained from a number of
different tests.
Since this test method quantifies only one small part of the complete vehicle handling characteristics, the
results of these tests can only be considered significant for a correspondingly small part of the overall
dynamic behaviour.
Moreover, insufficient knowledge is available concerning the relationship between overall vehicle dynamic
properties and accident avoidance. A substantial amount of work is necessary to acquire sufficient and
reliable data on the correlation between accident avoidance and vehicle dynamic properties in general
and the results of these tests in particular. Consequently, any application of this test method for regulation
purposes requires proven correlation between test results and accident statistics.

v
International Standard ISO 9815:2024(en)
Road vehicles — Passenger-car and trailer combinations —
Lateral stability test
1 Scope
This document specifies a lateral stability test for passenger-car and trailer combinations. It is applicable to
passenger cars in accordance with ISO 3833, and also to light trucks and their trailer combinations.
The lateral stability test determines the damping characteristic of the yaw oscillation of such towing-
vehicle–trailer combinations excited by a defined steering impulse. The combination is initially driven in a
steady-state, straight-ahead driving condition. Oscillation of the vehicle is then initiated by the application
of a single impulse of steering, followed by a period in which steering is held fixed and the oscillation of the
combination is allowed to damp out. Testing is conducted at several constant speeds. Where non-periodic
instability is of interest, a steady-state circular test is specified.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content constitutes
requirements of this document. For dated references, only the edition cited applies. For undated references,
the latest edition of the referenced document (including any amendments) applies.
ISO 2416, Passenger cars — Mass distribution
ISO 3833, Road vehicles — Types — Terms and definitions
ISO 8855, Road vehicles — Vehicle dynamics and road-holding ability — Vocabulary
ISO 15037-1:2019, Road vehicles — Vehicle dynamics test methods — Part 1: General conditions for passenger cars
3 Terms, definitions
For the purposes of this document, the terms and definitions given in ISO 3833, ISO 8855 and the following apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1
yaw articulation angle
Δψ
angle of the X axis relative to the X axis, i.e. angle between the X axes of each of the two units, with the
C T
polarity determined by the rotation of the towing vehicle relative to the trailer
Note 1 to entry: The letters “C” and “T” are used as subscripts to distinguish between variables associated with the
towing vehicle (car or light truck) and the trailer, respectively. For example, the longitudinal axis of the intermediate
axis system of the towing vehicle is designated as X , and the lateral acceleration of the trailer is designated as a .
C YT
3.2
mean gradient of the test track
G
change in elevation of the track surface between two points along the path of the vehicle divided by the
horizontal distance between those points, where the two points are those that define, as closely as is
practicable, that segment of the track travelled by the test vehicle between the times t and t , respectively
2 Δψn
for t and t , see 6.2.2 and 7.2.3, respectively
2 Δψn
Note 1 to entry: This gradient is dimensionless and is positive for a test vehicle travelling uphill and negative for a test
vehicle travelling downhill.
4 Measurement variables
When performing this test procedure, the following shall be measured:
— steering-wheel angle, δ ,
H
— longitudinal velocity of the towing vehicle, v ,
X
— lateral acceleration of the trailer, a ,
YT
— yaw articulation angle between towing vehicle and trailer, Δψ.
The following should be measured:
dψ
C
— yaw velocity of the towing vehicle, ;
dt
dψ
T
— yaw velocity of the trailer, .
dt
NOTE These variables are not intended to comprise a complete list.
5 General conditions
5.1 Conformity
The general conditions of the test shall be in accordance with ISO 15037-1, with the additions and exceptions
given in this clause.
5.2 Measuring equipment
The measurement variables given in Clause 4 shall be monitored using appropriate transducers. Typical
operating ranges and recommended maximum errors for variables are given in Table 1.
A steering-wheel stop or marking may be used. The use of a steering machine is optional.
Table 1 — Variables, operating ranges and recommended maximum errors
Recommended maximum error
Variable Typical operating range
(of combined transducer/recorder system)
Articulation angle ±20° ±0,2°
5.3 Test track
In addition to the test track requirements of ISO 15037-1, the mean gradient of the test track along the path
of the vehicle, G , shall be within the range ±0,01. G shall be recorded for each test run. See 6.2.1 and 7.2.1
for related requirements. In addition, the test surface shall be maintained over a track with a minimum
width of 8 m. An increased run-off area should be provided in addition to the specified test surface.

Yaw damping of articulated vehicles is sensitive to the longitudinal slope of the test track. The test should
therefore be conducted in both directions whenever G approaches the allowed maximum.
5.4 Wind velocity
Wind velocity shall be in accordance with ISO 15037-1 and, in addition, should not exceed 2,5 m/s.
5.5 Loading conditions
5.5.1 Towing vehicle
The total mass of the towing vehicle shall consist of the complete vehicle kerb mass (ISO 1176, code
ISO-M06) plus driver and instrumentation (combined mass should not exceed 150 kg). The location of the
instrumentation shall be such as to minimize its effect on the yaw moment of inertia of the towing vehicle.
The tests should be repeated at a maximum loading condition of the towing vehicle, at other loading
conditions of interest, or both. For the maximum loading condition, the total mass of a fully laden vehicle
shall consist of the complete vehicle kerb mass plus 68 kg for each seat in the passenger compartment, with
the static load at the coupling ball and the remaining maximum luggage mass equally distributed over the
luggage compartment in accordance with ISO 2416. Loading of the passenger compartment shall be such
that the actual wheel loads are equal to those obtained by loading each seat with 68 kg in accordance with
ISO 2416. The mass of instrumentation shall be included in the vehicle mass. Care shall be taken to ensure
that the moments of inertia are representative of the loading conditions of the vehicle in normal use.
The total mass of the fully laden towing vehicle, including the equivalent mass of the static load at the
coupling ball, shall not exceed the maximum design total mass (ISO 1176, code ISO-MO7), nor shall the
front and rear axle loads exceed their respective maximum design values with the load applied at the
coupling ball. If a load-distributing coupling is used, these axle loads should be assessed after engagement
of the load-distributing mechanisms (see 5.5.4), except where this is counter to the recommendations of the
manufacturer of the towing vehicle.
5.5.2 Trailer
The trailer shall be loaded to its maximum authorized total mass (ISO 1176, code ISO-M08) or until the
maximum design mass of vehicle combination (ISO 1176, code ISO-M18) is reached, whichever is the lesser
of the two masses. If the type of trailer allows various load distributions, the load shall be distributed in
such a way as to produce realistic and representative values of the yaw moment of inertia, centre-of-gravity
height and the static load at the coupling ball (see 5.5.3).
Optionally, tests may also be carried out with any other towed mass of interest.
The mass, centre-of-gravity position and yaw moment of inertia of the trailer as tested shall be measured
and noted in the general data (see Annex A). Alternatively, a description of the loading condition, adequate to
reproduce these properties with reasonable accuracy, shall be provided.
5.5.3 Static load on the coupling ball
Tests shall be carried out with the maximum permissible static load on the coupling ball as determined by
the maximum coupling load allowable for the towing vehicle, the trailer or the coupling itself, whichever is
the smallest. However, it is necessary to reduce further the static load on the coupling ball if it causes the load
on the rear axle of the towing vehicle to exceed the maximum design load as specified by the manufacturer
of the towing vehicle. Unless it is counter to the recommendations of that manufacturer, the rear-axle load is
to be assessed after the engagement of any load-distributing mechanism at the coupling.
The fraction of the weight of the trailer carried as static load on the hitch has an important influence on the
yaw damping of the vehicle combination. Typically, damping decreases as static load on the hitch decreases.
Therefore, tests should also be carried out with the minimum permissible static load at the coupling ball
(see ISO 1176).
5.5.4 Adjustment of load-distributing coupling mechanisms
When trailer mass is large, load-distributing couplings are often used to restore the pitch angle exhibited
by the towing vehicle prior to the application of a static load on the coupling. The addition of this moment
redistributes some of the coupling static load from the rear tyres to the front tyres of the towing vehicle and
the trailer tyres. This increases the articulation-angle damping but reduces the understeer of the towing
vehicle with lateral acceleration.
The load-distributing coupling ofte
...