Gravel Impact Test — SAE J400 / ASTM D3170

What Is Gravel Impact?

The gravel impact test evaluates the resistance of painted vehicle surfaces to impacts from stones and gravel thrown up from the road. Standard gravel is sprayed onto the specimen under controlled pressure and the resulting damage is graded. It is also known as the gravelometer test.

Purpose of Gravel Impact

The purpose is to determine how much the paint system resists chipping and substrate exposure under stone impact, and to compare different paint systems.

Which Products Is Gravel Impact Applied To?

Vehicle body painted panels
Bumper and undercarriage coatings
Wheel-rim coatings
Exterior parts exposed to stone impact

In Which Sectors Is Gravel Impact Used?

AutomotivePaint & CoatingMetal

Standards Related to Gravel Impact

SAE J400
ASTM D3170
ISO 20567-1
VDA 621-427

Gravel Impact Conditions

Gravel: Washed gravel with the size distribution defined in the standard
Pressure and quantity: Air pressure and gravel quantity prescribed by the standard
Specimen temperature: At room temperature or the low temperature specified in the specification
Impact angle: Fixed per the standard

Equipment for Gravel Impact

Gravelometer (gravel-impact test machine)
Compressed-air system
Conditioning/cooling chamber
Peel-tape material and assessment cards
Image-analysis system (optional)

Sample Requirements for Gravel Impact

Standard-size painted panels
Generally at least three specimens
The paint system's layer structure and film thickness must be stated
Specimens must be fully cured

Duration of Gravel Impact

The test itself is short per specimen; together with conditioning and assessment, the result is obtained within a few days.

Gravel Impact Procedure

1The specimen's film thickness is measured and recorded.
2The specimen is conditioned to the specified temperature, if required.
3The specimen is placed in the machine and fixed at the defined angle.
4A specified quantity of gravel is sprayed at the defined pressure.
5The specimen is removed; loose paint particles are lifted off with tape.
6The damage is compared with the standard's assessment cards.
7The damage grade and whether the substrate is exposed are reported.

Gravel Impact Acceptance Criteria

The acceptance criterion is the minimum grade defined in the OEM specification. Whether the damage reaches down to the metal is also evaluated as a separate acceptance criterion.

Evaluation of Results

Damage is graded by both size and count. Which layer the damage reaches down to (clear coat, base coat, primer, metal) is decisive in the evaluation; damage reaching the metal carries a corrosion-initiation risk.

Gravel Impact Report

Standard and method applied
Specimen description, paint system and film thicknesses
Test conditions (pressure, gravel quantity, temperature)
Damage grade for each specimen
Information on the layer reached by the damage
Photographs

Accreditation

EUROLAB holds internationally recognised accreditation obtained from accreditation bodies party to the IAF and ILAC multilateral recognition arrangements, under ISO/IEC 17025 for laboratory testing, ISO/IEC 17020 for inspection and surveillance, and ISO/IEC 17021-1 and ISO/IEC 17065 for system and product certification. This chain ensures the reports and certificates issued are accepted worldwide.

Whether this test can be offered within accredited scope depends on your product and the standard applied; since accreditation is method-based, the scope is confirmed in writing at the quotation stage.

Scope and authorisations

Related Regulations

OEM paint specifications

Otomotiv Testleri — What Does This Testing Field Cover?

The section below describes the field that the Gravel Impact test belongs to; the conditions and acceptance criteria of this particular test are given in the sections above. The scope specific to your product is confirmed in writing at the quotation stage.

Automotive testing shows that a component keeps working under conditions representing the loads it will meet over the life of the vehicle. A vehicle is not a single product but an ENVIRONMENT: vibration, temperature cycling, salt water, stone impact, electrical transients and electromagnetic noise are all present at the same time and for years.

What distinguishes this family is that VEHICLE MANUFACTURER SPECIFICATIONS sit on top of the standards. ISO and SAE publications establish the common ground; but Volkswagen, BMW, Ford, Stellantis, Toyota and Renault define different severity levels, additional tests and different acceptance criteria in their own specifications. For a component, the phrase "complies with automotive standards" is not sufficient on its own; which manufacturer's specification, and which revision of it, must be answered.

The family carries three separate processes together and they are often confused. Homologation covers the type approvals a vehicle needs to enter traffic and runs under state authority. Supplier approval means passing the vehicle manufacturer's own quality and testing requirements and is a commercial relationship. The third is design verification: the engineering team demonstrating that its own design meets its targets.

At component level the test plan is built around the LOCATION OF USE. A module in the engine bay and a module in the boot do not go through the same temperature and vibration profile; a component inside a door and one in the roof console do not see the same water and dust exposure. The ISO 16750 series is the common framework for this location-based approach.

The shift to electric vehicles has reshaped the field. High-voltage safety, insulation coordination, battery safety, charging interface conformity and the electromagnetic behaviour of high-voltage components have been added to the classical automotive test set. In a quiet vehicle, acoustic and vibration expectations have changed too; sounds once masked by the combustion engine are now audible.

The quality system side cannot be separated from testing in this field. A manufacturer under IATF 16949 presents test results in the PPAP file; measurement system analysis, process capability study and the control plan stand around the test report. A single good result is not enough — the process must be shown to be able to repeat it.

Method groups in this field

Environmental and climatic
Temperature cycling, thermal shock, damp heat, salt spray, dust and water ingress (IP), solar radiation. Severity levels vary with the mounting location.
Mechanical
Sine and random vibration, shock, mechanical loads, fastener torque and durability cycles.
Electrical
Supply voltage variations, transients (ISO 7637), reverse polarity, overvoltage, short circuit and sleep current measurements.
EMC
Component emissions (CISPR 25), radiated and conducted immunity (ISO 11452 series), electrostatic discharge (ISO 10605).
Materials and emissions
Odour, fogging and VOC emissions from interior materials; flammability; UV ageing; coating durability and stone impact.
Functional safety and cyber security
Functional safety evidence under ISO 26262 and cyber security engineering under ISO/SAE 21434; these are tied to regulation through UNECE R155 and R156.

Commonly confused in this field

An automotive report without a specification reference is not accepted in the supply chain; which OEM specification and revision was applied must be stated.
Type approval and supplier approval are different processes. A component with E-Mark approval is not thereby considered to have passed the OEM's own acceptance tests.
A result obtained on a prototype does not carry over to series production; PPAP is done with series production parts.
On the EMC side, measuring emissions alone is incomplete; immunity is a separate body of work and is more critical in a vehicle.
On electric vehicle components, high-voltage safety is a distinct competence; classical 12 V test infrastructure is not sufficient.

Which decisions these results support

Supplier component approval and the PPAP file
UNECE type approval and E-Mark marking
Design verification and durability evidence
Root cause analysis of field complaints and warranty returns
Assessing the impact of a design or supplier change

Related Tests

Frequently Asked Questions About Gravel Impact

Why is testing at low temperature requested?

The paint film becomes brittle at low temperature and its resistance to stone impact decreases. Many OEM specifications require the test to be performed at low temperature to represent winter conditions.

Is the gravel impact test the same as the stone-chip test?

They evaluate the same phenomenon, and the terms are often used interchangeably. Different standards use different rigs and grading; which standard applies depends on the specification.