ISO 8349:2002

Overview - ISO 8349:2002 (Road vehicles - Measurement of road surface friction)

ISO 8349:2002 defines standardized test methods to measure the longitudinal friction properties of paved surfaces using either a standard reference test tyre (SRTT) or the tyre of a test vehicle. Its purpose is to harmonize friction results across different test tracks by specifying procedures to determine peak‑braking and slide‑braking coefficients under controlled surface conditions. The standard describes three alternative constant‑speed approaches and includes normative annexes for reference tyre specifications and calibration, plus guidance on wet surface measurements.

Key topics and technical requirements

• Three accepted measurement methods:
  • Constant‑speed, transient braking force method - progressive brake application to obtain spot measurements of peak and slide friction (typical test speed cited: 65 km/h).
  • Constant‑speed, constant‑braking slip method - continuous measurement at a fixed slip (0–40%) to map peak friction along the track and obtain spot slide values.
  • Constant‑speed, fixed‑braking slip method - economical continuous method using a small SRTT (4.00‑8) for uniformity checks and reference values.
• Definitions of peak‑braking coefficient (ratio of maximum braking force to simultaneous vertical load) and slide‑braking coefficient (sliding wheel longitudinal force averaged for 1 s beginning 0.2 s after lockup).
• Instrumentation and data acquisition requirements: longitudinal force, vertical load (dynamic or corrected static), and vehicle speed recording.
• Calibration and reference tyre specifications provided in Annex A and Annex B; wet surface guidance in Annex C.
• Notes on variability: friction values are time‑ and condition‑dependent (environment, contamination, surface age) and may not directly correlate with other measuring methods.

Applications and who uses it

• Road and test‑track authorities for establishing reference friction levels and track uniformity.
• Automotive manufacturers and test laboratories for vehicle handling and braking tests that require standardized surface friction data.
• Tyre manufacturers for comparative evaluation of tyre–road interaction representative of passenger‑car tyres.
• Regulatory bodies and research organizations for harmonizing friction measurements across facilities.

ISO 8349:2002 is particularly useful when consistent, comparable friction reference numbers are needed for pavement evaluation, brake/handling tests, and tyre performance assessment.

Related standards

• ISO 8855 (vehicle dynamics vocabulary)
• Referenced ASTM standards (e.g., ASTM E1136, E1551, E274) cited in ISO 8349 for tyres, calibration and comparative methods
• Note: UNECE K methods and other locked‑wheel procedures are discussed in the introduction for context but are not adopted within ISO 8349.

Keywords: ISO 8349:2002, road surface friction measurement, standard reference test tyre, SRTT, peak‑braking coefficient, slide‑braking coefficient, constant‑speed friction test, pavement friction, test track uniformity.