For decades, vehicle emissions regulation concentrated primarily on what came out of the exhaust. Euro 7 changes that perspective by bringing another important source of road-transport pollution directly into the homologation framework: particles generated by brakes and tyres.
These non-exhaust emissions create an important regulatory shift because they are not limited to vehicles with combustion engines. Battery-electric vehicles have no tailpipe emissions during electric operation, yet their brakes and tyres can still generate particulate emissions through friction, wear and abrasion.
Brake particle measurement has now progressed from research methodology to an internationally harmonized regulatory framework, while tyre-abrasion measurement and limits are moving through their own regulatory development path. Together, these requirements are expanding the meaning of vehicle emissions homologation.
Vehicle Emissions No Longer Begin and End at the Tailpipe
Successive generations of vehicle-emissions legislation have substantially reduced many pollutants emitted by modern combustion engines.
As exhaust-emission controls have improved and vehicle fleets have progressively electrified, other sources of particulate emissions have become increasingly important.
Friction between brake pads and discs can release particles into the surrounding environment.
Continuous interaction between tyres and road surfaces causes material loss throughout tyre life.
Vehicle-road interaction can also contribute to particulate material generated during transport.
Vehicle movement can contribute to previously deposited road dust becoming airborne again.
Regulation historically concentrated heavily on pollutants produced by the combustion process and emitted through the vehicle exhaust.
The regulatory boundary expands to include particulate emissions associated with braking and tyre abrasion, regardless of whether the vehicle has a tailpipe.
Every Friction Brake Creates Wear
Conventional friction braking converts vehicle kinetic energy into heat through contact between braking surfaces. That friction inevitably produces wear.
Part of the resulting material can become airborne particulate matter, creating a direct link between brake-system engineering and environmental emissions performance.
Pad formulation can significantly influence wear behaviour and particle generation.
Disc composition, surface treatment and wear characteristics interact with the friction material.
Brake temperature and thermal history influence friction behaviour and particle formation.
Braking intensity, frequency and energy determine how the friction pair is exercised during operation.
It must provide the stopping performance required for vehicle safety while also controlling the particulate emissions generated through friction.
A Global Method for Measuring Brake Emissions
A regulatory emissions limit is meaningful only when laboratories can measure emissions using a sufficiently harmonized and repeatable procedure.
UN Global Technical Regulation No. 24 established an internationally harmonized laboratory methodology for measuring brake emissions from light-duty vehicles.
Brake-emissions research could use different cycles, measurement systems and laboratory conditions, making results difficult to compare directly.
Standardized test principles provide a common technical basis for measuring and comparing brake particle emissions.
From Vehicle Operation to Controlled Laboratory Measurement
Brake particle testing requires much more than placing a particle counter beside a brake disc.
The test environment needs to reproduce defined braking behaviour while controlling the conditions that influence particle generation, transport and measurement.
The brake assembly is operated under controlled conditions representing the applicable vehicle and braking characteristics.
Defined braking events reproduce representative braking activity through a standardized laboratory sequence.
Thermal conditions are controlled and monitored because temperature strongly influences wear and particle generation.
Generated particles must be transported through a controlled sampling environment suitable for measurement.
PM measurements quantify the mass of brake-generated particulate matter within defined size fractions.
Particle-number measurement provides an additional characterization of emitted brake particles where applicable.
Brake wear is influenced by temperature, pressure, speed, friction pairing and previous braking history. Homologation therefore depends on tightly controlled test preparation and execution.
Brake Emissions Become a Quantified Homologation Requirement
Euro 7 moves brake emissions beyond measurement alone by establishing particulate-emission limits for applicable vehicles.
Initial Euro 7 PM10 Limits — M1 & N1 Vehicles
The above values apply to the Euro 7 standard driving-cycle limits for the relevant M1 and N1 vehicle categories through 31 December 2029. Separate limits apply to N1 Class III vehicles, and the regulatory framework provides for later-stage limits and further development.
Electrification Changes the Brake-Emissions Equation
In an electrified vehicle, deceleration does not always require the friction brakes to absorb the vehicle’s kinetic energy.
Regenerative braking can use the electric propulsion system to slow the vehicle while recovering energy into the traction battery.
Pads and discs create braking force through friction, producing heat and material wear.
The propulsion system contributes to deceleration, reducing the amount of braking energy that must be absorbed through friction.
Friction brakes remain necessary for safety, emergency braking, low-speed operation and conditions in which regenerative braking is unavailable or insufficient.
The Second Non-Exhaust Emissions Frontier
Every tyre gradually loses material as it rolls, accelerates, brakes and corners against the road surface.
Euro 7 brings tyre abrasion into the vehicle-emissions regulatory framework, creating requirements that ultimately extend beyond vehicle manufacturers to tyre design, testing and type approval.
Rubber formulation influences wear resistance, grip, rolling resistance and other performance characteristics.
Loads transmitted through the tyre can influence wear and abrasion behaviour.
Acceleration, braking and cornering intensity can affect the rate of tyre wear.
Surface characteristics, temperature and environmental conditions influence abrasion.
Inflation pressure affects tyre deformation, contact characteristics and wear.
Alignment and suspension characteristics can significantly influence tread wear patterns.
How Do You Measure Something That Wears Slowly?
Brake emissions can be evaluated through highly controlled laboratory testing. Tyre abrasion presents a different measurement challenge because wear develops progressively through interaction between the tyre, vehicle, road and environment.
The regulatory objective is therefore to establish sufficiently repeatable and representative methods for comparing tyre abrasion performance.
Test conditions need to control or account for variables that can significantly influence tyre wear.
Tyres require sufficient operation to generate measurable and representative abrasion.
Changes in tyre mass can provide a basis for determining material loss over the test distance.
Results require appropriate normalization so that tyres can be compared through a consistent abrasion metric.
Manufacturers should distinguish carefully between requirements already fixed in legislation and measurement procedures or abrasion limits that remain subject to international and European regulatory development.
Lower Wear Cannot Come at the Expense of Safety
Non-exhaust emissions regulation introduces a classic engineering optimization problem.
Brake and tyre systems cannot simply be redesigned to minimize material wear without considering the safety and performance functions they must provide.
Lower-wear friction materials must still deliver predictable braking, thermal stability, durability, corrosion resistance and acceptable performance across operating conditions.
Lower-abrasion tyres must continue to satisfy requirements for wet grip, braking, structural integrity, rolling resistance and other performance characteristics.
What Happens After the Original Brakes and Tyres Wear Out?
Brake pads, brake discs and tyres are wear components. Unlike many vehicle systems, they are expected to be replaced repeatedly during the service life of the vehicle.
This creates an important regulatory question: the environmental performance achieved by the original vehicle should not necessarily disappear when replacement components are fitted.
The vehicle is homologated with defined brake and tyre configurations contributing to its original regulatory performance.
Replacement friction components can influence both braking characteristics and particulate-emission behaviour.
Tyres fitted later in the vehicle’s life can have different abrasion characteristics from the original equipment.
Regulatory control increasingly needs to consider products entering the replacement market as well as original vehicle production.
The International Framework Is Still Developing
Brake and tyre particle regulation is moving rapidly from technical research into formal type-approval requirements.
Established the internationally harmonized laboratory methodology for measuring brake emissions from light-duty vehicles.
WP.29 adopted a new UN Regulation in 2026 establishing internationally harmonized brake-particle measurement and emission-limit requirements for light-duty vehicles.
European legislation introduces quantitative brake-particle limits and provides for further development of future requirements.
International work continues on measurement methodology and the regulatory framework needed to implement abrasion limits across tyre classes.
Later phases of the Euro 7 framework extend non-exhaust-emissions regulation across additional vehicle categories.
Regulatory work is also examining particulate-emission requirements for replacement brake components.
The measurement procedures, vehicle categories, implementation dates and limits are developing at different speeds. A compliance strategy based only on today’s requirements may therefore be insufficient for a vehicle or component programme reaching the market several years later.
Preparing for Non-Exhaust Emissions Homologation
Brake and tyre emissions need to be considered early in product development because they interact with vehicle architecture, component selection, safety performance and future replacement-part strategies.
Identify applicable Euro 7, UN and national requirements according to vehicle category, tyre class, powertrain and market.
Establish friction materials, disc technologies, regenerative-braking strategy and expected emissions performance.
Define the appropriate brake-emissions test programme, laboratory capability, conditioning and measurement requirements.
Evaluate tyre wear characteristics together with safety, rolling resistance, durability and vehicle-specific operating conditions.
Coordinate brake, friction-material and tyre suppliers so that component evidence supports the complete homologation programme.
Track evolving UN and Euro 7 requirements, future limits, implementation dates and replacement-component developments.
A New Definition of a Clean Vehicle
Vehicle emissions regulation is entering a new phase.
Controlling combustion emissions remains important, but electrification means the environmental performance of a vehicle can no longer be assessed only through its exhaust.
Brake systems generate particles. Tyres lose material throughout their operating life. Both processes occur regardless of whether propulsion comes from petrol, diesel, hydrogen or electricity.
Emissions regulation focuses predominantly on pollutants created by the vehicle’s powertrain.
Exhaust, brakes, tyres and other environmental characteristics progressively form part of a broader vehicle-emissions conformity framework.
As tailpipe emissions disappear from electric vehicles, the environmental performance of brakes, tyres and other non-exhaust sources becomes increasingly visible and increasingly regulated.