ISO/PAS 13146:2024

Road vehicles - Brake lining friction materials - Drag mode friction test for hydraulic and pneumatic vehicle brakes

This document specifies a method for the drag mode friction test for hydraulic and pneumatic vehicle brakes. This document is applicable to the friction performance test of brake linings used in vehicles of categories M, N, O, and L.

Véhicules routiers — Matériaux de friction des garnitures de freins — Essai de frottement pour les freins hydrauliques et pneumatiques de véhicules

General Information

• Status: Published
• Publication Date: 12-Nov-2024
• ICS: 43.040.40 - Braking systems
• Technical Committee: ISO/TC 22/SC 33 - Vehicle dynamics and chassis components
• Drafting Committee: ISO/TC 22/SC 33 - Vehicle dynamics and chassis components
• Current Stage: 6060 - International Standard published
• Start Date: 13-Nov-2024
• Due Date: 24-Mar-2025
• Completion Date: 13-Nov-2024

Overview

ISO/PAS 13146:2024 - Road vehicles - Brake lining friction materials - Drag mode friction test for hydraulic and pneumatic vehicle brakes - specifies a laboratory method to evaluate the friction performance of brake linings using a constant-speed drag mode. The Publicly Available Specification targets brake linings for vehicle categories M, N, O, and L and provides procedures and requirements for test benches, sample preparation, temperature measurement and result evaluation. The method simulates realistic braking conditions while focusing on the friction material rather than full vehicle assemblies.

Key topics and technical requirements

• Test scope and applicability: Drag mode friction test for hydraulic and pneumatic vehicle brakes; applicable to brake linings for vehicle categories M, N, O and L.
• Test equipment: Use of a calibrated test bench with fixtures to mount calipers and rotors (see Annex A). Effective friction radius is adjustable per requester or Annex B.
• Sample preparation and conditioning: New production linings required; surface coatings removed; rotors cleaned and conditioned by at least one complete test programme before reporting.
• Test procedures: Two control modes are specified - constant torque mode and constant pressure mode - with defined test cycles and evaluation steps. Methods A and B cover different brake assembly types and sampling approaches.
• Measurement and evaluation: Coefficients of friction (cold, operational, minimum/maximum, fading) and wear are measured and reported. Brake torque calculation and templates are provided (Annex C and D).
• Temperature measurement: Thermocouple installation is the reference - for ventilated rotors located 0.5 mm below the friction surface in the outer ring; for solid rotors positioned halfway through the friction ring thickness. Alternative methods (IR, rubbing thermocouple) may be used after validation.
• Quality limits and rotor reuse: Rotor discard guidance based on wearable thickness (manufacturer spec or 90% rule) and surface roughness/torque variation thresholds are included.

Applications

• Material development: early product screening and comparative performance testing of friction formulations.
• Quality control: production lot testing, process control and consistency checks for brake linings.
• Supplier/OEM evaluation: selecting and validating friction materials for hydraulic and pneumatic brake systems without full dynamometer or vehicle testing.
• Research and R&D: studying friction behavior, wear trends and temperature effects under drag-mode conditions.

Who should use this standard

• Brake friction material manufacturers and R&D teams
• Automotive OEMs and brake system engineers
• Independent test laboratories and certification bodies
• Quality assurance teams in braking component supply chains

Related standards

• ISO 611 (Road vehicles - Braking vocabulary) is referenced for terminology. For implementation details and national adoption, consult your national ISO member body.

Keywords: ISO/PAS 13146:2024, brake lining friction materials, drag mode friction test, hydraulic and pneumatic brakes, brake testing, coefficients of friction, brake rotor temperature measurement.

Standards Content (Sample)

Publicly
Available
Specification
ISO/PAS 13146
First edition
Road vehicles — Brake lining
2024-11
friction materials — Drag mode
friction test for hydraulic and
pneumatic vehicle brakes
Véhicules routiers — Matériaux de friction des garnitures de
freins — Essai de frottement pour les freins hydrauliques et
pneumatiques de véhicules
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: [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 Symbols . 2
5 Test conditions . 2
5.1 Test equipment and parts .2
5.2 Requirement .2
5.3 Brake temperature measurement .3
6 Test type. 4
7 Method A: Brake lining assemblies for vehicles of categories M , M , N , O , O and L . 4
1 2 1 1 2
7.1 General .4
7.2 Determination of test pressure and torque .4
7.2.1 Determination of test pressure and torque of the original sample method .4
7.2.2 Determination of test pressure and torque of the sampling method .5
7.3 Brake rotor and brake caliper conditions .5
7.4 Sample preparation .5
7.4.1 Sample preparation of the original sample method .5
7.4.2 Sample preparation of the sampling method .6
7.5 Thickness and mass measurement .6
7.6 Test procedure .6
7.6.1 Test procedure 1: Constant torque mode .6
7.6.2 Test procedure 2: Constant pressure mode .7
7.7 Evaluation of test results.8
7.7.1 General .8
7.7.2 Cold coefficients of friction and coefficients of friction during normal operation .8
7.7.3 Minimum, maximum and fading coefficients of friction .10
8 Method B: Rotor and drum brake lining assemblies for vehicles of categories M , N , N ,
3 2 3
O and O .12
3 4
8.1 General . 12
8.2 Determination of test pressure for sampling method . 13
8.3 Brake rotor and brake caliper conditions for the sampling method . 13
8.4 Sample preparation . 13
8.5 Thickness and mass measurement . 13
8.6 Test procedure . 13
8.7 Evaluation of test results.14
9 Test report .15
Annex A (normative) Test bench. 16
Annex B (informative) Effective friction radius (r ) . 17
eff
Annex C (normative) Brake torque .18
Annex D (informative) Templates .29

iii
Foreword
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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
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This document was prepared by Technical Committee ISO/TC 22, Road vehicles, Subcommittee SC 33, Vehicle
dynamics, chassis components and driving automation systems testing.
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
Assessing friction performance is a primary concern when developing friction materials and conducting
quality control. The brake assembly simulation test plays an important role here. However, the dyno test
is not adapted to all vehicle models and brakes, and the assembly test is expensive and time-consuming.
Therefore, a test method that can simulate real working conditions while only targeting friction materials is
needed for the quality control of friction materials.
There are two ways to evaluate the friction performance of vehicle friction materials. One is through
constant speed dragging, and the other is deceleration braking. The constant speed dragging braking mode
can be used for the small sample test and assembly test. This braking mode is similar to actual driving
conditions, brake system characteristics and automotive vehicle dynamics.
This document proposes a constant speed dragging test procedure for vehicle friction materials, which is
used to evaluate the consistency of the performance of friction materials. Users assess and report on the test
result according to their own specific requirements, such as friction levels or brake lining or rotor wear.
This test procedure has the following characteristics.
— The test data is comparable to the full-size assembly test.
— The test results can be used to compare friction materials.
— The test method is used to test the performance of friction materials. The test can be applied to raw
material screening, early product development, process quality control and sample testing. The test is
also an important means to test product consistency and quality control.
— The test method is made more efficient by using full-size brake linings, calipers and rotors. It is less
expensive than testing on a full-size dynamometer test bench.

v
Publicly Available Specification ISO/PAS 13146:2024(en)
Road vehicles — Brake lining friction materials — Drag mode
friction test for hydraulic and pneumatic vehicle brakes
1 Scope
This document specifies a method for the drag mode friction test for hydraulic and pneumatic vehicle brakes.
This document is applicable to the friction performance test of brake linings used in vehicles of categories M,
N, O, and L.
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 611, Road vehicles — Braking of automotive vehicles and their trailers — Vocabulary
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 611 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
cycle
braking process consisting of several brake applications
Note 1 to entry: Each braking cycle consists of several brake applications or brake manoeuvres.
Note 2 to entry: Each individual braking manoeuvre consists of a 5 s application of the brake followed by a 10 s brake
release.
3.2
constant torque mode
control mode for maintaining constant braking torque during braking process
3.3
constant pressure mode
control mode for maintaining constant line pressure during braking process

4 Symbols
Table 1 — Symbols, definitions and units
Symbol Definition Unit
A area of caliper piston(s) cm
k
A radiating surface of brake rotor(s) m
BS
c specific heat storage capacity J/(N K)
p
g gravity acceleration m/s
G weight of brake rotor; G = m g
N
BS BS BS
m mass of rotor kg
BS
M , M , M , M torque N m
d 1 2 3
-1
n speed r min
P applied pressure MPa
r brake effective radius mm
eff
t time s
T initial temperature °C
Initial
T final temperature °C
end
T final temperature K
E
T start temperature K
A
α
transmission coefficient J/(m s K)
η efficiency —
μ friction coefficient —
μ fading coefficient of friction —
F
μ cold coefficient of friction —
K
μ maximum coefficient of friction —
max
μ minimum coefficient of friction —
min
μ operational coefficient of friction —
op
5 Test conditions
5.1 Test equipment and parts
The test shall be conducted using a test bench with appropriate hardware and software as specified in
Annex A.
A suitable fixture shall be used to mount the brake caliper on the test bench so that the brake caliper and
the brake rotor stay in position. The effective friction radius is adjusted according either to the requester
specification or to Annex B.
Before starting the test, the entire system, including the brake caliper, shall be adequately bled. Assembling
the caliper shall not interfere with the torque measurement.
5.2 Requirement
New brake linings from current production shall be used. For pads with a surface coating, the coating shall
be removed before assembling the test configuration. The brake caliper and rotor to be used shall be as
specified by the test requester.
New brake rotors shall be thoroughly cleansed to remove any corrosion protection coatings. The brake rotor
may be reused until the minimum thickness specified by the manufacturer is reached. In the absence of a
specification, discard the rotor when it reaches 90 % of the wearable thickness.

Before each test, the surface of the brake rotor shall be cleaned with sandpaper to remove wear marks and
rust from the surface. Dust and oil on the surface of the brake rotor should be removed with a soft cloth or
anhydrous ethanol.
Recondition a new or reworked brake rotor by conducting at least one complete test programme with the
same friction material intended for the tests. Do not include these conditioning tests as part of the report. It
is recommended to use a single rotor for each lining material. The same applies to every re-use of the rotor
after a period in storage.
Replace the brake rotor when the torque variations exceed ±5 % of the set value or the surface roughness
exceeds 15 µm. Measure roughness in the radial direction in the middle of the friction ring at three or more
equally spaced angular positions.
On calipers with integral parking brakes, remove the mechanical parking brake actuation (spindle) to
minimize efficiency loss and to simplify the retraction of the piston when changing a pad.
When a vehicle has several variants of brake rotors for a given brake pad number, use the variant with the
highest (most critical) ratio of kinetic energy to rotor mass.
5.3 Brake temperature measurement
The temperature is measured at the outboard side of the rotor by means of an embedded (caulked)
thermocouple, in the friction effective radius (see Annex B) it is measured at the surface of a thermocouple
pressed in by a copper pin. For alternative temperature measurement methods, the fixed thermocouple is
the reference sensor:
— in the case of ventilated brake rotors in the outer friction ring, located at 0,5 mm below friction surface
(see Figure 1);
— in the case of solid brake rotors half way up the friction ring thickness (see Figure 2).
After demonstrating that the alternative temperature measurement method is comparable to the standard
thermocouple installation, an infrared or rubbing thermocouple measurement methods can be used. Aim
for a measurement position as close as possible to the equivalent thermocouple. Record the measurement
position in the comparison test report. The rotor runout shall be measured when the brake rotor is mounted
on the test bench. The maximum permissible rotor runout is 0,08 mm.
Key
1 brake rotor
2 thermocouple
r brake effective radius
eff
Figure 1 — Example of a ventilated brake rotor

Key
1 brake rotor
2 thermocouple
r brake effective radius
eff
Figure 2 — Example of a solid brake rotor
6 Test type
The two test types are the original sample method and the sampling method. The original sample method is
used to test the original size of the sample (the original brake lining). The sampling method is used to shrink
a brake lining to a specified size to be tested in a standardized brake application.
Brake lining assemblies for vehicles of categories M, N, O and L can be tested using either the original sample
method or the sampling method.
7 Method A: Brake lining assemblies for vehicles of categories M , M , N , O , O and L
1 2 1 1 2
7.1 General
For this category of vehicles, the test types are the original method and the sampling method.
7.2 Determination of test pressure and torque
7.2.1 Determination of test pressure and torque of the original sample method
7.2.1.1 Determination of test pressure
The hydraulic pressure, P, under the piston(s) of the caliper shall be constant when calculated using
Formula (1):
M
d
P = (1)
0,57⋅⋅rA
wk
where
M is the braking torque, expressed in N m;
d
A is the area of the caliper piston(s), expressed in m ;
k
r is the effective radius of the rotor, expressed in m;
w
— when A ≤ 18,1 cm , M is 150 N m;
k d
— when A > 18,1 cm , M is 300 N m.
k d
NOTE The total piston area acting on one side of the caliper is considered, regardless of the number of pistons.
7.2.1.2 Determination of test torque
The brake torque, M, shall be constant when calculated in accordance with Annex C, Formula (C.1).
7.2.2 Determination of test pressure and torque of the sampling method
In constant pressure mode, the mean contact pressure at the brake lining friction surface shall be constant
at (75 ± 10) N/cm . The mean brake line pressure shall be constant at 0,89 MPa.
In constant torque mode, M is 103 N m, M is 186 N m and M is 194 N m.
1 2 3
7.3 Brake rotor and brake caliper conditions
When conducting the original sample method, the brake rotor and brake caliper shall meet the requirements
specified in the drawings and technical documentation of the brake application used.
When conducting the sampling method, a fixed rotor brake caliper with a piston diameter of 36 mm shall be
installed on the test machine. The effective friction radius (see Annex B) shall be 116,5 mm after installation.
The brake rotor is solid with a diameter of (278 ± 2) mm and a thickness of (9 ± 0,5) mm and made of
standard grey cast iron materials.
7.4 Sample preparation
7.4.1 Sample preparation of the original sample method
Select a brake lining at random from the samples to be tested and mark five points (point 1 to point 5) on the
back of the lining. These are the points at which thickness is measured (see Figure 3). Determine the average
wear by taking the arithmetic mean of all the points measured. If the measurement at point no. 5 is located
on the groove, offset the measurement point horizontally by 10 mm.
Dimensions in mm
Figure 3 — Position of thickness measurement points

7.4.2 Sample preparation of the sampling method
Randomly select a brake lining from the samples to be tested. Cut a rectangular piece of the friction material,
with a length of (40,0 ± 0,2) mm, a width of (30,0 ± 0,2) mm and a thickness of no less than 5,0 mm from the
middle of the brake lining. The test piece shall fit tightly to the carrier plate (see Figure 4).
If the brake lining is too small to take the friction material (40 mm × 30 mm), randomly select two brake
linings from the samples to be tested, take two rectangular pieces of friction material and assemble them
into the specified size. The difference in thickness between the two rectangular pieces of friction materials
shall not exceed 0,05 mm. Mark four points on the sample non-friction surface as positions for thickness
measurement (see Figure 4).
Dimensions in mm
Figure 4 — Position of thickness measurement points
7.5 Thickness and mass measurement
Wear shall be determined by weighing the sample and measuring thickness before and after the test.
Measure and record the thickness of each measurement point to an accuracy of 0,01 mm. Weigh and record
the mass of the sample to an accuracy of 0,01 g.
7.6 Test procedure
7.6.1 Test procedure 1: Constant torque mode
The braking interval consists of:
— 5 s braking time;
— 10 s idle time between signal brake off and on.
The rotor speed shall be:
−1
— n = 660 r min = constant.
No cooling air is applied during the test cycles, only exhaust air is extracted.

Table 2 — Constant torque test programme
Test pro-
Brake applications Brake torque
a
gramme
Cycle T [°C] T [°C]
Initial End
per cycle M
d
groups
I. Burnish 1—6 5 M 100 (the first brake < 50) Max. 250
II. μ 7 5 M < 60 300—350
K1 2
III. μ 8—10 5 M 100 300—350
op1 2
IV.μ 11 10 M 100 500—550
F1 3
V. μ 12—15 5 M 100 300—350
op2 2
VI. μ 16 10 M 100 500—550
F2 3
VII. μ 17—19 5 M 100 300—350
op3 2
VIII. μ 20 5 M < 60 300—350
K2 2
a
Temperature values are determined by the programme flow. For group I (Burnish procedure), interrupt the cycle when the
temperature T reaches 250 °C. For subsequent cycles, continue with a T of 100 °C.
End Initial
For brake torques, see Annex C, which is valid for standard grey cast iron materials only. For other materials,
the brake torques shall be recalculated using the specific material parameters in accordance with the
requester’s specifications.
During all cycles, exhaust air extraction is on and cooling air application is off. Cooling is on between cycles
when the rotor shall cool down to T .
Initial
7.6.2 Test procedure 2: Constant pressure mode
The braking interval consists of:
— 5 s braking time;
— 10 s idle time between signal brake off and on.
The rotor speed shall be:
−1
— n = 660 r min = constant.
Cooling is on during the Burnish group, last test group and between the cycles when the rotor shall cool
down to T . The exhaust air extracted is on during the entire test programme.
Initial
Apply a constant hydraulic pressure, P, to the caliper piston(s) as presented in Formula (1) (7.2.1.1).
Table 3 — Constant pressure test programme
Initial brake
Test pro-
rotor Max. brake rotor
Brake applica- Forced cool-
gramme Cycle
tions per cycle ing
temperature temperature [°C]
groups
[°C]
1 — 6 100 (the first
I. Burnish 5 200 Yes
brake < 50)
II. 7 10 ≤ 60 No limitation No
a
III. 8 — 12 10 100 No limitation (350) No
IV. 13 10 100 No limitation Yes
a
For vehicles of category L, the temperature shall be limited to 350 °C. If necessary, the number of applications
per cycle shall be reduced accordingly. However, in this case, the number of cycles shall be increased to keep the
total number of applications constant.

7.7 Evaluation of test results
7.7.1 General
Carry out a visual inspection of the test samples. The detachment of the friction material from the backing
plate shall be documented. Tearing of the pad, structural cracks, spalling, plasticity, inclusion of casting
particles in the friction surface of the pad, noise and brake rotor condition (hotspots, cracks) shall be noted.
Only measured torque values shall be used to calculate the coefficients of friction. The test value of the
actual values shall be recorded with a scanning frequency of a minimum of 20 Hz.
Unless otherwise specified by the entity that requested the test, the constants used to calculate the friction
coefficients are η = 0,95 for sliding calipers and η = 0,98 for fixed calipers.
The test report shall include the following characteristic values and tolerance bands:
for the constant torque method:
— cold coefficients of friction, μ , μ ;
K1 K2
— coefficients of friction during normal operation, μ , μ , μ ;
op1 op2 op3
NOTE 1 This can be represented as μ or μ .
op B
— fading coefficients of friction, μ , μ ;
F1 F2
— minimum coefficient of friction, μ ;
min
— maximum coefficient of friction, μ ;
max
— wear (weight and thickness variation for the single sample);
for the constant pressure method:
— cold coefficient of friction, μ ;
K
— coefficient of friction during normal operation, μ ;
op
NOTE 2 This can be represented as μ or μ .
op B
— fading coefficient of friction, μ ;
F
— minimum coefficient of friction, μ ;
min
— maximum coefficient of friction, μ ;
max
— wear (weight and thickness variation for the single sample).
Additional friction coefficients and specific tolerances should be agreed with the entity that requested the test.
7.7.2 Cold coefficients of friction and coefficients of friction during normal operation
To determine the cold coefficient(s) of friction and the coefficient(s) of friction during normal operation,
calculate the coefficients of friction after one second. To this end, all values measured during one brake
application shall be averaged when torque or pressure reach 80 % + 1 s in the time window of ±0,1 s (see
Figure 5 for the constant torque method and Figure 6 for the constant pressure method).

Key
t time
μ coefficient of friction
M controlled variable torque
1 cold coefficient of friction, μ / coefficient of friction during normal operation, μ or μ
K op B
Figure 5 — Example of cold coefficients of friction and coefficients of friction during normal
operation for the constant torque method

Key
t time
μ coefficient of friction
P controlled variable pressure
1 cold coefficient of friction, μ / coefficient of friction during normal operation, μ or μ
K op B
Figure 6 — Example of cold coefficients of friction and coefficients of friction during normal
operation for the constant pressure method
The cold coefficients of friction, μ , μ , are the coefficients of friction after one second of the first brake
K1 K2
application. This applies to each first cycle in test programme group II (Table 2) and the last cycle in test
programme group VIII (Table 2) for the constant torque method. The cold coefficient of friction, μ , is the
K
coefficient of friction after one second of the first brake application of the first cycle in test programme group
II (Table 3) for the constant pressure method. The starting temperature of each of these brake applications
is 60 °C.
The coefficients of friction during normal operation are the coefficients of friction after one second of each
first brake application. This applies to cycles with a starting temperature of 100 °C, i.e. groups III, V and VII
(Table 2) for the constant torque method and groups III and IV (Table 3) for the constant pressure method.
In the constant torque method, three coefficients of friction during normal operation shall be determined
in groups III and VII (Table 2). Four coefficients shall be determined in group V (Table 2). The single values
are combined into one mean value for each group: μ , μ , μ . In the constant pressure method, six
op1 op2 op3
coefficients of friction during normal operation shall be determined in groups III and IV (Table 3). The single
values are combined into one m
...