ISO 21755-3:2025

Motorcycles - Measurement method for evaporative emissions - Part 3: VT-SHED test procedure

This document specifies a basic measurement method by using the variable temperature sealed housing for evaporative determination (VT-SHED) test procedure for evaporative emissions from motorcycles. It is applicable to motorcycles equipped with a spark ignition engine (four-stroke engine, two-stroke engine or rotary piston engine).

Motocycles — Méthode de mesure pour les émissions par évaporation — Partie 3: Protocole d'essai VT-SHED

General Information

• Status: Published
• Publication Date: 13-Nov-2025
• ICS: 13.040.50 - Transport exhaust emissions
• ICS: 43.140 - Motorcycles and mopeds
• Technical Committee: ISO/TC 22 - Road vehicles
• Drafting Committee: ISO/TC 22 - Road vehicles
• Current Stage: 6060 - International Standard published
• Start Date: 14-Nov-2025
• Due Date: 13-Jan-2026
• Completion Date: 14-Nov-2025

Overview

ISO 21755-3:2025 - "Motorcycles - Measurement method for evaporative emissions - Part 3: VT‑SHED test procedure" specifies a standardized method for measuring evaporative emissions from motorcycles using the variable temperature sealed housing for evaporative determination (VT‑SHED). Applicable to motorcycles with spark‑ignition engines (four‑stroke, two‑stroke, or rotary piston), the standard defines the test sequence, equipment, calibration and result presentation for accurate assessment of fuel‑vapour losses such as diurnal breathing loss (DBL) and hot soak loss (HSL).

Key topics and technical requirements

• Scope and test structure: The VT‑SHED test comprises conditioning and test phases to simulate real‑world temperature variation and usage patterns.
• Test motorcycle and fuel: Vehicles should be run at least 1 000 km before testing; test fuel selection and vapour pressure must be agreed among parties and reported.
• Test sequence: Procedures include pre‑soaking, pre‑conditioning drive, fuel drain/refill steps, start soaking, carbon canister loading, dynamometer driving, hot soak loss (HSL) and diurnal breathing loss (DBL) measurements.
• Evaporative emission enclosure (VT‑SHED): A gas‑tight, hydrocarbon‑nonreactive chamber with controlled temperature profiling. The temperature control must follow the prescribed diurnal profile with an average tolerance of ±1 K and interior surface limits between 278.2 K and 328.2 K.
• Chassis dynamometer: Single‑roll dynamometer with roll diameter ≥ 0.400 m and roll revolution counter to measure distance; running resistance setup per ISO 11486.
• Analytical systems and calibration: Hydrocarbon analysers, pressure and temperature recording systems and chamber calibration (volume, background emissions, retention) are required. Clause 5 addresses calibration frequency and methods.
• Result calculation and reporting: Methods for calculating evaporative emission totals and standardized test reporting formats are defined.

Practical applications and users

ISO 21755-3:2025 is designed for:

• Motorcycle manufacturers performing design validation and production compliance testing.
• Independent test laboratories conducting certification and conformity assessment.
• Regulatory agencies defining evaporative emission limits and test protocols.
• R&D teams studying fuel system design, canister performance and fuel‑vapour mitigation strategies.

Typical uses include type‑approval testing, development of evaporative control systems (canisters, purge strategies), and comparative research into fuel vapour behavior under variable temperatures.

Related standards

This part is part of the ISO 21755 series and references other motorcycle testing standards, including:

• ISO 21755‑1:2019 (SHED test procedure)
• ISO 4106 (engine net power)
• ISO 6460‑1 and ISO 6460‑2 (gaseous exhaust emissions and test cycles)
• ISO 7117 (maximum speed)
• ISO 11486 (dynamometer running resistance)

Keywords: ISO 21755-3:2025, VT‑SHED, motorcycle evaporative emissions testing, diurnal breathing loss, hot soak loss, evaporative emission enclosure, chassis dynamometer, hydrocarbon analyser.

Standards Content (Sample)

International
Standard
ISO 21755-3
First edition
Motorcycles — Measurement
2025-11
method for evaporative
emissions —
Part 3:
VT-SHED test procedure
Motocycles — Méthode de mesure pour les émissions par
évaporation —
Partie 3: Protocole d'essai VT-SHED
Reference number
© ISO 2025
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: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland
ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Evaporative emissions . 2
4.1 Description of VT- SHED test .2
4.2 Test motorcycle and fuel .3
4.2.1 Test motorcycles .3
4.2.2 Test fuel .3
4.3 Test equipment .4
4.3.1 Chassis dynamometer .4
4.3.2 Evaporative emission measurement enclosure .4
4.3.3 Analytical systems .5
4.3.4 Temperature recording system .5
4.3.5 Pressure recording system .5
4.3.6 Fans .6
4.3.7 Gases.6
4.3.8 Additional equipment .6
4.4 Test procedure .6
4.4.1 Test preparation .6
4.4.2 Fuel drain and refill .7
4.4.3 Pre-soaking .7
4.4.4 Pre-conditioning drive .7
4.4.5 Fuel drain and refill .7
4.4.6 Start soaking .7
4.4.7 Carbon canister loading .7
4.4.8 Dynamometer test .8
4.4.9 Hot soak loss (HSL) test.8
4.4.10 Soak .9
4.4.11 Diurnal breathing loss (DBL) test .9
4.5 Calculation of results .10
5 Calibration of equipment for evaporative emission testing .12
5.1 Calibration frequency and methods . 12
5.2 Calibration of the enclosure . 12
5.2.1 Initial determination of internal volume of the enclosure . 12
5.2.2 Determination of chamber background emissions . 12
5.2.3 Calibration and hydrocarbon retention test of the chamber . 13
5.3 Analytical systems .14
5.3.1 General .14
5.3.2 Hydrocarbon analyser .14
5.3.3 Hydrocarbon analyser data recording system . 15
5.3.4 Checking of FID hydrocarbon analyser . 15
6 Presentation of results . 16
6.1 The evaporative emission .16
6.2 Test report .16
Annex A (normative) Presentation of results for evaporative emissions . 17
Bibliography .20

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.
This document was prepared by Technical Committee ISO/TC 22, Road vehicles, Subcommittee SC 38,
Motorcycles and mopeds.
A list of all parts in the ISO 21755 series can be found on the ISO website.
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
Recently, exhaust emissions from tailpipes of motorcycles have been dramatically reduced. Accordingly,
evaporative emissions have begun to attract attention. Therefore, measurement methods for evaporative
emissions are specified as an International Standard for multi-application, for example, certification,
research, developments and so on.
For motorcycles, the measurement method based on the sealed housing for evaporative determination
(SHED) method was conventionally specified, but not for the variable temperature sealed housing for
evaporative determination (VT-SHED) method, which matches the actual usage environment and has a high
accuracy of the test system. This document specifies the basic measurement method by using the VT-SHED
test procedure for evaporative emissions from motorcycles.

v
International Standard ISO 21755-3:2025(en)
Motorcycles — Measurement method for evaporative
emissions —
Part 3:
VT-SHED test procedure
1 Scope
This document specifies a basic measurement method by using the variable temperature sealed housing
for evaporative determination (VT-SHED) test procedure for evaporative emissions from motorcycles. It is
applicable to motorcycles equipped with a spark ignition engine (four-stroke engine, two-stroke engine or
rotary piston engine).
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 4106, Motorcycles — Engine test code — Net power
ISO 6460-1:2022, Motorcycles — Measurement method for gaseous exhaust emissions and fuel consumption —
Part 1: General test requirements
ISO 6460-2, Motorcycles — Measurement method for gaseous exhaust emissions and fuel consumption — Part
2: Test cycles and specific test conditions
ISO 7117, Motorcycles — Measurement method for determining maximum speed
ISO 11486, Motorcycles — Methods for setting running resistance on a chassis dynamometer
ISO 21755-1:2019, Motorcycles — Measurement method for evaporative emissions — Part 1: SHED test
procedure
3 Terms and definitions
For the purposes of this document, the following terms and definitions 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
evaporative emissions
hydrocarbon vapor lost from the fuel storage and supply system of a motorcycle and not those from tailpipe
emissions
3.2
variable temperature sealed housing for evaporative determination test
VT-SHED test
motorcycle test in a variable temperature sealed house for evaporative determination, in which a special
evaporative emission test is conducted
3.3
diurnal breathing loss
DBL
hydrocarbon emissions caused by temperature changes in the fuel storage
3.4
hot soak loss
HSL
hydrocarbon emissions arising from the fuel system of a stationary motorcycle after a period of driving
3.5
non-exposed fuel tank
fuel tank, except the fuel tank cap, which is not directly exposed to radiation of sunlight
3.5.1
exposed fuel tank
fuel tank directly exposed to radiation of sunlight
3.6
nominal capacity
fuel capacity of the fuel tank as declared by the manufacturer
3.8
2 g breakthrough
condition considered accomplished when the cumulative quantity of hydrocarbons emitted from the
activated carbon canister equals 2 g
4 Evaporative emissions
4.1 Description of VT- SHED test
The evaporative emission VT-SHED (variable temperature sealed housing for evaporative determination)
test consists of a conditioning phase and a test phase (see Figure 1).

Figure 1 — Flowchart of evaporative emission VT-SHED test
4.2 Test motorcycle and fuel
4.2.1 Test motorcycles
The test motorcycle shall be run for at least 1 000 km after the first start on the production line.
At the request of the tester, non-fuel background emission sources (e.g. paint, adhesives, plastics, fuel
and vapour lines, tyres, and other rubber or polymer components) may be reduced to typical motorcycle
background levels before testing (e.g. baking of tyres at temperatures of 323,2 K or higher for appropriate
periods, baking of the motorcycle).
4.2.2 Test fuel
The test fuel shall be selected in agreement among the parties involved or the manufacturer's requirements,
and the specifications of test fuel shall be reported. The record form is given in Clause A.3.
NOTE This test is influenced by the vapour pressure of the fuel property greatly, therefore, the test vapour
pressure is decided among the parties because the market fuel vapour pressure largely varies according to the season
depending on the area.
4.3 Test equipment
4.3.1 Chassis dynamometer
The dynamometer shall have a single roll with a diameter of at least 0,400 m.
The dynamometer shall be equipped with a roll revolution counter for measuring the distance travelled.
The methods for setting running resistance on a chassis dynamometer shall be in accordance with ISO 11486.
4.3.2 Evaporative emission measurement enclosure
4.3.2.1 General
The evaporative emission measurement enclosure shall be a gas-tight rectangular measuring chamber able
to contain the motorcycle under test. The motorcycle shall be accessible from all sides and the enclosure
when sealed shall be gas-tight in accordance with 5.2.3. The inner surface of the enclosure shall be
impermeable and non-reactive to hydrocarbons. The temperature conditioning system shall be capable of
controlling the internal enclosure air temperature to follow the prescribed temperature versus time profile
throughout the test, and an average tolerance of 1 K over the duration of the test.
The control system shall be tuned to provide a smooth temperature pattern that has a minimum of
overshoot, hunting, and instability about the desired long-term ambient temperature profile. Interior
surface temperatures shall not be less than 278,2 K nor more than 328,2 K at any time during the diurnal
emission test.
Wall design shall be such as to promote good dissipation of heat. Interior surface temperatures shall not be
below 293,2 K, nor above 325,2 K for the duration of the hot soak test.
To accommodate the volume changes due to enclosure temperature changes, either a variable-volume or
fixed-volume enclosure may be used.
4.3.2.2 Variable-volume enclosure
The variable-volume enclosure expands and contracts in response to the temperature change of the air mass
in the enclosure. Two potential means of accommodating the internal volume changes are movable panel(s),
or a bellows design, in which an impermeable bag or bags inside the enclosure expand(s) and contracts(s)
in response to internal pressure changes by exchanging air from outside the enclosure. Any design for
volume accommodation shall maintain the integrity of the enclosure as specified in 5.2 over the specified
temperature range.
Any method of volume accommodation shall limit the differential between the enclosure internal pressure
and the barometric pressure to a maximum value of ±0,5 kPa.
The enclosure shall be capable of latching to a fixed volume. A variable volume enclosure shall be capable of
accommodating a +7 % change from its "nominal volume" (see 5.2.1.1), taking into account temperature and
barometric pressure variation during testing.
4.3.2.3 Fixed-volume enclosure
4.3.2.3.1 The fixed-volume enclosure shall be constructed with rigid panels that maintain a fixed enclosure
volume and meet the requirements in 4.3.2.3.2 and 4.3.2.3.3.
4.3.2.3.2 The enclosure shall be equipped with an outlet flow stream that withdraws air at a low, constant
rate from the enclosure throughout the test. An inlet flow stream may provide make-up air to balance
the outgoing flow with incoming ambient air. Inlet air shall be filtered with activated carbon to provide a
relatively constant hydrocarbon level. Any method of volume accommodation shall maintain the differential
between the enclosure internal pressure and the barometric pressure between 0 kPa and -0,5 kPa.

4.3.2.3.3 The equipment shall be capable of measuring the mass of hydrocarbon in the inlet and outlet flow
streams with a resolution of 0,01 g. A bag sampling system may be used to collect a proportional sample of
the air withdrawn from and admitted to the enclosure. Alternatively, the inlet and outlet flow streams may
be continuously analysed using an on-line flame ionisation detector (FID) analyser and integrated with the
flow measurements to provide a continuous record of the mass hydrocarbon removal.
4.3.3 Analytical systems
4.3.3.1 Hydrocarbon analyser
4.3.3.1.1 The atmosphere within the enclosure shall be monitored using a hydrocarbon detector of the FID
type. Sample gas shall be drawn from the midpoint of one side wall or the roof of the enclosure and any bypass
flow shall be returned to the enclosure, preferably to a point immediately downstream of the mixing fan.
4.3.3.1.2 The hydrocarbon analyser shall have a response time to 90 % of final reading of less than 1,5 s.
Its stability shall be better than 2 % of full scale at zero and at 80 % ± 20 % of full scale over a 15 min period
for all operational ranges.
4.3.3.1.3 The repeatability of the analyser expressed as one standard deviation shall be better than 1 % of
full-scale deflection at zero and at 80 % ± 20 % of full scale on all ranges used.
4.3.3.1.4 The operational ranges of the analyser shall be chosen to give best resolution over the
measurement, calibration and leak checking procedures. The leak checking procedure shall be accordance
with analyser manufacture.
4.3.3.2 Hydrocarbon analyser data recording system
The hydrocarbon analyser shall be fitted with a device to record electrical signal output either by strip chart
recorder or other data-processing system at a frequency of at least once per minute. The recording system
shall have operating characteristics at least equivalent to the signal being recorded and shall provide a
permanent record of results. The record shall show a positive indication of hot soak periods together with
the time elapsed between start and completion of each test.
4.3.4 Temperature recording system
4.3.4.1 The temperature recording system shall meet the requirements of 4.3.4.2 to 4.3.4.4.
4.3.4.2 The temperature in the chamber is recorded at two points by temperature sensors which are
connected so as to show a mean value. The measuring points are extended approximately 0,1 m into the
enclosure from the vertical centre line of each side wall at a height of 0,9 m ± 0,2 m.
4.3.4.3 Temperatures shall, throughout the evaporative emission measurements, be recorded or entered
into a data processing system at a frequency of at least once per minute.
4.3.4.4 The accuracy of the temperature recording system shall be within ±1,0 K and the temperature
shall be capable of being resolved to ±0,4 K.
The recording or data processing system shall be capable of resolving time to ±15 s.
4.3.5 Pressure recording system
4.3.5.1 The pressure recording system shall meet the requirements of 4.3.5.2 to 4.3.5.4.

4.3.5.2 The difference Δp between barometric pressure within the test area and the enclosure internal
pressure shall, throughout the evaporative emission measurements, be recorded or entered into a data
processing system at a frequency of at least once per minute.
4.3.5.3 The accuracy of the pressure recording system shall be within ±0,3 kPa and the pressure shall be
capable of being resolved to ±0,025 kPa.
4.3.5.4 The recording or data processing system shall be capable of resolving time to ±15 s.
4.3.6 Fans
4.3.6.1 The fans shall meet the requirements of 4.3.6.2 and 4.3.6.3.
4.3.6.2 By the use of one or more fans or blowers with the SHED door(s) open, it shall be possible to reduce
the hydrocarbons concentration in the chamber to the ambient hydrocarbon level.
4.3.6.3 The chamber shall have one or more fans or blowers with which to thoroughly mixing of the air in
the enclosure. The fan or blower shall provide a nominal total flow rate of (0,8 ± 0,2) m /min per nominal
enclosure volume V . It shall be possible to attain an even temperature and hydrocarbon concentration in the
n
chamber during measurements. The motorcycle in the enclosure shall not be subjected to a direct stream of
air from the fans or blowers.
4.3.7 Gases
4.3.7.1 The gases shall meet the requirements of 4.3.7.2 and 4.3.7.3.
4.3.7.2 The following pure gases shall be available for calibration and operation:
a) purified synthetic air: (purity: < 1 ppm C equivalent, ≤ 1 ppm CO, ≤ 400 ppm CO , ≤ 0,1 ppm NO); oxygen
1 2
content between 18 % and 21 % by volume;
b) hydrocarbon analyser fuel gas: (40 % ± 2 % hydrogen, and balance helium or nitrogen with less than
1 ppm C equivalent hydrocarbon, less than 400 ppm CO );
1 2
c) propane (C H ):99,5 % minimum purity;
3 8
d) butane (C H ):98 % minimum purity;
4 10
e) nitrogen (N ):98 % minimum purity.
4.3.7.3 Calibration and span gases shall be available containing mixtures of propane (C H ) and purified
3 8
synthetic air. The true concentrations of a calibration gas shall be within 2 % of the stated figures. The
accuracy of the diluted gases obtained when using a gas divider shall be to within ±2 % of the true value. The
concentrations specified in 5.2.3 and 5.3.3 may also be obtained by the use of a gas divider using synthetic
air as the dilutant gas.
4.3.8 Additional equipment
The barometric pressure in the test area shall be measurable within ±0,1 kPa.
4.4 Test procedure
4.4.1 Test preparation
The motorcycle is mechanically prepared before the test as follows:
a) the exhaust system of the motorcycle shall not exhibit any leaks;

b) the motorcycle may be steam cleaned before the test;
c) additional fittings, adaptors or devices may optionally be fitted to allow a complete draining of the fuel
tank. Alternatively, the fuel tank may be evacuated by means of a pump or siphon that prevents fuel
spillage; and
d) the evaporative emission co
...