Comparison of Tire Friction Test Methodologies Used in Accident Reconstruction

Many accident reconstructions rely on the use of friction factors for the analysis of vehicle speeds. Measurement of the friction factor, or coefficient of friction, at the accident site is usually an important step in achieving a more accurate estimate of the friction factor at the time of the accident. Over the years several on site test methodologies have emerged within the accident reconstruction community. However, little has been published which compares the data and results from the different methods.

This paper presents a comparison of some methodologies. A g-analyst¹ accelerometer, a VC•2000² accelerometer, and a bumper chalk gun³/radar gun⁴ are compared for locked wheel friction values under different speed and road surface conditions. Data from the two on board systems are recorded simultaneously. Measurements are made for several stops at each of the speeds and two road surface conditions. Statistical analysis is performed on each test method for each set of test conditions to determine repeatability of that test method. These statistical analyses also indicate what real differences can be attributed to the experimental factors.