ISO 14792:2011

Road vehicles - Heavy commercial vehicles and buses - Steady-state circular tests

ISO 14792:2011 specifies tests for determining the steady-state directional control response of heavy vehicles, one of the factors composing vehicle dynamics and road-holding properties. ISO 14792:2011 is applicable to heavy vehicles, i.e. commercial vehicles, combinations, buses and articulated buses as defined in ISO 3833, covered by Categories M3, N2, N3, O3, and O4 of UNECE (United Nations Economic Commission for Europe) and EC vehicle regulations. These categories pertain to trucks and trailers with a maximum mass above 3,5 t and to buses and articulated buses with a maximum mass above 5 t.

Véhicules routiers — Véhicules utilitaires lourds et autobus — Essais sur trajectoire circulaire en régime permanent

General Information

• Status: Published
• Publication Date: 10-Mar-2011
• ICS: 43.080.01 - Commercial vehicles in general
• Technical Committee: ISO/TC 22/SC 33 - Vehicle dynamics and chassis components
• Drafting Committee: ISO/TC 22/SC 33/WG 6 - Vehicle dynamics of heavy commercial vehicles and buses
• Current Stage: 9060 - Close of review
• Completion Date: 04-Mar-2030

Relations

• Revises: ISO 14792:2003 - Road vehicles - Heavy commercial vehicles and buses - Steady-state circular tests
• Effective Date: 21-Aug-2010

Overview

ISO 14792:2011 - "Road vehicles - Heavy commercial vehicles and buses - Steady‑state circular tests" defines standardized test procedures to quantify the steady‑state directional control response of heavy vehicles. Applicable to vehicles defined in ISO 3833 and UNECE/EC Categories M3, N2, N3, O3, O4, this ISO standard focuses on the vehicle dynamics and road‑holding properties assessed through controlled circular turning tests (steady‑state circular tests).

Key topics and technical requirements

• Test objectives: Characterize steady‑state turning behaviour (left and right turns) for heavy commercial vehicles, combinations, buses and articulated buses.
• Test types:
  • Constant radius test - drive the vehicle on a known circular path at constant speed; repeat at increasing speeds and on at least three radii (standard radius recommended: 100 m).
  • Constant speed, variable‑steer angle test - drive at constant speed with fixed steer angle; repeat at increasing steer angles and at three or more speeds (standard speed recommended: 50 km/h).
• Variables & reference system: Use variables per ISO 15037‑2 and ISO 8855; reference point is the vehicle unit’s centre of gravity.
• Measuring equipment & data handling: Equipment and recording shall comply with ISO 15037‑2 requirements.
• Test conditions & tolerances:
  • Maintain average speed within ±2 km/h (±3 km/h permissible deviation).
  • Collect steady‑state data for at least 3 s; standard deviation of centripetal acceleration ≤ 0.25 m/s² during acquisition.
  • Increment centripetal acceleration in steps ≤ 0.5 m/s² when selecting successive speeds or steer angles.
• Data analysis: Report steady‑state averages for measured variables; evaluate steering‑wheel angle variation, centripetal acceleration (from lateral accel. corrected for sideslip, yaw × speed, v² / radius, etc.), and curvature (from radius, yaw/velocity, or a_c/v²).
• Safety considerations: Estimate rollover limits before testing; avoid exceeding ~75% of the rollover estimate and consider anti‑rollover outriggers. Monitor tyre temperature to prevent heat‑induced property changes.

Applications and who uses it

ISO 14792:2011 is used by:

• Vehicle manufacturers and R&D engineers to validate handling and steady‑turn performance of trucks, trailers and buses.
• Test labs and certification bodies conducting comparative handling tests and development validation.
• Fleet safety analysts and vehicle dynamics specialists assessing cornering behaviour, stability margins and tuning steering systems. Practical uses include design validation, comparative benchmarking, component tuning (suspension/steering/tyres) and regulatory or research studies relating to heavy vehicle road‑holding.

Related standards

• ISO 15037‑2: General conditions for heavy vehicles and buses (measuring equipment, test environment)
• ISO 3833: Vehicle types - terms and definitions
• ISO 8855: Vehicle dynamics vocabulary and reference frames

Keywords: ISO 14792:2011, steady‑state circular tests, heavy commercial vehicles, buses, vehicle dynamics, road‑holding, constant radius test, constant speed variable‑steer angle test, centripetal acceleration.

Standards Content (Sample)

INTERNATIONAL ISO
STANDARD 14792
Second edition
2011-03-15
Road vehicles — Heavy commercial
vehicles and buses — Steady-state
circular tests
Véhicules routiers — Véhicules utilitaires lourds et autobus — Essais
sur trajectoire circulaire en régime permanent

Reference number
©
ISO 2011
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ii © ISO 2011 – All rights reserved

Contents Page
Foreword .iv
Introduction.v
1 Scope.1
2 Normative references.1
3 Test objectives.1
4 Variables and reference system .2
5 Measuring equipment .2
6 Test conditions .2
7 Test procedures.3
7.1 General .3
7.2 Constant radius test.3
7.3 Constant speed, variable-steer angle test .3
7.4 Common test conditions .3
8 Data analysis.4
8.1 General .4
8.2 Steering-wheel angle.4
8.3 Centripetal acceleration.4
8.4 Curvature of trajectory.4
9 Data evaluation and presentation of results .4
9.1 General .4
9.2 Other evaluations and presentation of results.5
Annex A (normative) Test report — Presentation of results.8
Bibliography.13

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.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. ISO shall not be held responsible for identifying any or all such patent rights.
ISO 14792 was prepared by Technical Committee ISO/TC 22, Road vehicles, Subcommittee SC 9, Vehicles
dynamics and road-holding ability.
This second edition cancels and replaces the first edition (ISO 14792:2003), of which it constitutes a minor
revision.
iv © ISO 2011 – All rights reserved

Introduction
The main purpose of this International Standard 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
will require proven correlation between test results and accident statistics.
INTERNATIONAL STANDARD ISO 14792:2011(E)

Road vehicles — Heavy commercial vehicles and buses —
Steady-state circular tests
1 Scope
This International Standard specifies tests for determining the steady-state directional control response
of heavy vehicles, one of the factors composing vehicle dynamics and road-holding properties. It is applicable
to heavy vehicles, i.e. commercial vehicles, combinations, buses and articulated buses as defined in ISO 3833,
covered by Categories M3, N2, N3, O3, and O4 of UNECE (United Nations Economic Commission for
Europe) and EC vehicle regulations. These categories pertain to trucks and trailers with a maximum mass
above 3,5 t and to buses and articulated buses with a maximum mass above 5 t.
2 Normative references
The following referenced documents are indispensable for the application 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 3833, Road vehicles — Types — Terms and definitions
ISO 8855, Road vehicles — Vehicle dynamics and road-holding ability — Vocabulary
ISO 15037-2:2002, Road vehicles — Vehicle dynamics test methods — Part 2: General conditions for heavy
vehicles and buses
3 Test objectives
The general conditions for
⎯ variables,
⎯ measuring equipment and data processing,
⎯ environment (test track and wind velocity),
⎯ test vehicle preparation (tuning and loading),
⎯ initial driving, and
⎯ the reporting of general data and test conditions
of general significance, independent of the specific vehicle dynamics test procedure, shall be as specified in
ISO 15037-2. They shall apply when vehicle dynamics properties are determined unless other conditions are
required in the standard for the test procedure actually used.
Although this International Standard is intended for combination vehicles as well as for single-unit vehicles,
Clauses 8 and 9, regarding data analysis, evaluation and presentation, deal only with the motion variables of
the single-unit vehicle or of the first unit of combinations. Thus, in order to comply with this International
Standard, the user shall meet the requirements for variables, measuring equipment and data handling only in
as far as they apply to the single-unit vehicle or to the first unit of combinations. Nevertheless, users are
encouraged to measure and analyse the motions of trailing units as appropriate to their particular purposes.
The primary objective of this test procedure is to determine the steady-state turning characteristics of heavy
vehicles for both left- and right-hand turns.
The steady-state turning behaviour of unit vehicles which have more than two axles and/or dual or wide-base
tyres, as is the case with most heavy vehicles, is known to be a strong function of both centripetal acceleration
[3][4]
and path curvature . To characterize the steady-state behaviour of these vehicles, it is therefore necessary
to conduct turning tests on different radii turns as well as at varying levels of centripetal acceleration. Such a
test program may be accomplished through a series of constant radius tests conducted at various radii, or
through a series of constant speed, variable-steer angle tests conducted at different speeds. Indeed, it is
desirable that both types of tests be conducted for a full characterization of the steady-state turning of these
vehicles.
The constant radius test requires the test vehicle to be driven at a constant speed on a path of known,
constant radius. The directional control response characteristics are determined from data obtained by
repeating the procedure at successively higher speeds. To fully characterize the steady-turning of the vehicle,
this procedure shall then be repeated for various radii. The procedure may be tailored to existing test track
facilities by selecting circles or paths of appropriate radii.
The constant speed, variable-steer angle test requires the test vehicle to be driven at a constant speed and
constant steer angle. The directional control response characteristics are determined from data obtained by
repeating the procedure at successively greater steer angles. To fully characterize the steady-turning of the
vehicle, this procedure shall then be repeated at various speeds.
4 Variables and reference system
The variables to be determined may be selected for test purposes from those given in ISO 15037-2 and shall
be monitored using appropriate transducers. The variables relate to the intermediate axis system (X, Y, Z)
(see ISO 8855).
For the purposes of this International Standard, the reference point shall be the centre of gravity of the vehicle
unit.
This provision overrides the similar provision of ISO 15037-2.
Strictly speaking, the steady-state turning performance ought to be evaluated based on centripetal
acceleration, a , rather than on lateral acceleration, a , (see ISO 8855). In most practical situations, however,
c Y
the difference between these two quantities is small and can be ignored. Nevertheless, in a few cases
(e.g. long-wheelbase vehicles operating on small turning radii or any vehicle operating at large body sideslip
angles), the difference could be appreciable. In these cases, measured lateral acceleration needs to be
corrected for sideslip angle to determine centripetal acceleration. In any case, this document refers to
centripetal acceleration throughout rather than to lateral acceleration.
5 Measuring equipment
The measuring and recording equipment shall be in accordance with ISO 15037-2.
6 Test conditions
The limits and specifications for ambient and vehicle test conditions shall be in accordance with ISO 15037-2.
2 © ISO 2011 – All rights reserved

7 Test procedures
7.1 General
The general test specifications shall be in accordance with ISO 15037-2.
7.2 Constant radius test
During this test procedure, the vehicle shall be steered such that it moves on a circular path at a constant
speed. Repeat the procedure at successively faster speeds. The entire procedure should be repeated on
paths of at least three different radii.
A standard radius of 100 m should be used for one of the paths. The radii of the other paths should span the
largest range practicable. The significance of the results improves with increases in the range and number of
radii. Whichever the radii chosen, the vehicle shall be steered such that the reference point of the first unit
remains within 0,5 m of the intended circular path.
For each radius chosen, conduct the test at several speeds. The first speed shall be the slowest practical
speed. Choose successive speeds such that the increments of centripetal acceleration are not more than
0,5 m/s . Where the data vary rapidly with centripetal acceleration, it could be useful to make smaller
incremental changes.
7.3 Constant speed, variable-steer angle test
During this test procedure, the vehicle shall be driven at a constant speed and constant steer angle. Repeat
the procedure at successively larger steer angles. The entire procedure should be repeated applying at least
three different speeds.
The standard speed should be 50 km/h and additional speeds covering the broadest range practicable are
also recommended. A test at a very slow speed is desirable. The significance of the results improves with
increases in the range and number of speeds.
For each test run, maintain the average speed within a tolerance of ± 2 km/h of the selected speed.
A deviation of the vehicle speed of ± 3 km/h from the selected speed is permissible.
For each test speed, conduct tests at several levels of constant steer angle. The first steer angle shall be the
smallest practical deflection from the straight-ahead position. Choose successive steer angles such that the
increments of centripetal acceleration are no more than 0,5 m/s . At slower speeds, where large changes of
steer angle produce little change in centripetal acceleration, it could be useful to make smaller incremental
changes.
7.4 Common test conditions
For each test, maintain the steering-wheel position and the vehicle speed as constant as possible during the
acquisition of the data. Take data for at least 3 s at each steady-state centripetal acceleration. During this time
period, the standard deviation of centripetal acceleration shall not exceed 0,25 m/s .
Take data for both left and right turns. All the data may be taken in one direction followed by all the data in the
other direction. Alternatively, data may be taken successively in one direction and in the other for each
acceleration level, going from the lowest to the highest. Note the method in accordance with Annex A.
The range of centripetal accelerations covered should be as large as is practicable. However, a careful
estimation of the rollover limit of the test vehicle should be made prior to testing. Special care should be taken
whenever centripetal acceleration of a test might exceed 75 % of this estimate. The use of anti-rollover
outriggers should be considered for any
...