This test method covers the measurement of the longitudinal friction coefficient with a measurement device that imposes braking-slip between a tire and a surface for the full range of braking-slip speed values.
This test method utilizes a series of incremental single measurements of friction force on a braked test wheel as it is pulled over a wetted or contaminated pavement surface. The rotational velocity of the braked wheel is feedback controlled in order to give a predetermined variable slip ratio gradient in accordance with set program parameters. The test wheel is kept under a constant static normal load and at a constant longitudinal speed of travel. Its major plane is perpendicular to the road plane and parallel to its direction of motion.
The values measured represent the friction properties obtained with the equipment and procedures stated in this test method and do not necessarily agree or correlate directly with those obtained by other pavement friction measuring methods.
The values are intended for use in:
Evaluating the braking friction forces on a pavement relative to that of other pavements.
Evaluating changes in the braking friction forces of a particular pavement with the passage of time.
Evaluating the changes in the braking friction force of a pavement when subjected to polishing wear and loss of macrotexture caused by traffic with passage of time.
Evaluating changes in the braking friction forces of a pavement contaminated with ice, moderate amounts2 of slush and snow, pollen, vehicle oil spills and condensates from vehicle engine exhaust, and deposits from other pollution sources.
Evaluating the braking friction forces of a specimen tire on a clean or contaminated pavement.
The friction values reported by this test method are insufficient to determine the distance required to stop a vehicle on either a dry, wet, or contaminated pavement. They are also insufficient for determining the speed at which control of a vehicle would be lost.
The values stated in SI units are to be regarded as the standard. The inch-pound values given in parentheses are provided for information only.
This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. Specific precautionary statements are given in Section 6 and Note 4.
2 Slush thickness less than 25 mm (1 in.). Loose snow thickness less than 50 mm (2 in.).