Brake-particle measurement is based on UN GTR No. 24, adopted in June 2023 as the world’s first harmonized brake-emissions procedure. Its binding type-approval form, UN Regulation No. 179, was adopted at WP.29 in March 2026 and is expected to take effect in September 2026.

The test runs a complete brake corner—disc, pads, and caliper—on an inertia dynamometer inside a sealed, cooled enclosure. The enclosure is supplied with HEPA (H13) and activated-carbon-filtered air to ensure that measured particles are attributed to the brake system.

The brake test is using the WLTP-Brake cycle. It is based on real-world driving data from 5 world regions, 10 trips, and 303 brake events over about 192 km.

Downstream of the enclosure, the sampled air splits into two isokinetic lines. These lines draw the particles through PM10 and PM2.5 cyclones and then into gravimetric filter holders.

The filter weighing that follows uses the same differential weighing method applied in gravimetric particulate-matter testing for exhaust and ambient PM. In parallel, a separate line sends the sample through a volatile-particle remover before it reaches the particle counter.

The process converts corner-level measurements into the final vehicle result in three steps:

Each brake corner is tested separately

Each brake corner is tested separately

The results are weighted to reflect the contribution of each axle

The results are weighted to reflect the contribution of each axle

The weighted values are combined into a single vehicle emission (mg/km)

The weighted values are combined into a single vehicle emission (mg/km)

Filter Weighing Guide

Filter Weighing Guide for Compliant Emissions Testing

Improve Emissions Measurement Accuracy and Support Regulatory Readiness

Emissionsprüfung – Gravimetrische Bestimmung von Feinstaub

Emissionsprüfung – Gravimetrische Bestimmung von Feinstaub

Filterwägung zur gravimetrischen Bestimmung von Feinstaub in Motorabgasen und Verdunstungsemissionen

What does Euro 7 brake particle emissions testing measure?

Euro 7 brake particle emission testing measures the particulate matter released by a vehicle’s brakes during a standard drive cycle. The process works in three steps:

  • a brake corner runs on a dynamometer inside a filtered enclosure;

  • particles are captured on PTFE filters; and

  • each filter is weighed before and after the test.

The filter’s mass gain is divided by the distance driven to produce a result in mg/km, which is then checked against the applicable Euro 7 limit.

What limits does Euro 7 set for brake emissions?

For light-duty vehicles, Euro 7 sets PM10 brake-emission limits that vary by vehicle class and powertrain. During the interim period to the end of 2034, the main limits are:

  • 7 mg/km for combustion M1 and N1 class I-II vehicles;

  • 3 mg/km for battery-electric M1 and N1 class I-II vehicles; and

  • 11 mg/km for N1 class III vehicles to the end of 2029.

From 2035, the limit drops to 3 mg/km for M1 and N1 class I-II vehicles across all powertrains. The limit for N1 class III is still to be defined. Particle number is measured under the method, but it is not yet capped.

What balance is required for brake-wear filter weighing?

Brake-wear filter weighing requires more from a balance than 0.1 µg readability. Accurate results depend on three elements:

  • A (ultra)-microbalance with sufficient measurement repeatability to quantify the small filter mass gains

  • Control of environmental and electrostatic influences through proper filter conditioning, handling, and weighing procedures

  • Documented measurement traceability, including calibration records and evidence that the balance performs adequately for the expected filter mass gains.

The XPR3U Ultra-Microbalance meets the resolution and minimum-weight requirements. For reliable results, it should be paired with Universal Antistatic Kit.

Why is static charge important in brake-filter weighing?

PTFE membranes can hold electrostatic charges. That charge can influence the balance and bias the reading by about 1 µg, even after neutralization.

At 0.1 µg readability, the error from static charge on a filter can exceed the measurement uncertainty of the balance itself. Measure the charge on each filter and remove it before you record the filter mass; without that measurement, residual charge remains an unquantified error in the result.

How many weighings are needed in one brake-test campaign?

 A brake-test campaign requires far more weighings than the number of filters. In one documented example, a single cycle of three runs with four filters each involves:

  • 12 filters in total;

  • 24 sample weighings, one tare and one loaded reading per filter;

  • 48 blank and reference weighings in the ABA scheme that brackets every sample weighing.

Together, these steps add up to 72 individual weighings for one cycle, and a campaign repeats them for every cycle. At that number, automated filter weighing removes most of the manual handling and keeps each weighing step repeatable.

Will China 7 include brake-emissions requirements?

China 7 (国七) is expected to include non-exhaust emissions from brakes and tires into type approval. The methods and limits are still under study, and no official number has been published yet.

 The regulatory direction has prompted many labs to build gravimetric weighing capacity now, before the final text is published.

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