Variability of Yaw Calculations from Field Testing

This paper discusses the variability of critical speed calculations from controlled field tests. A total of 29 tests were conducted at speeds of 80 to 95 km/h, using three different vehicles, three tire types, and variable braking levels. Results of the testing are provided. Analysis of the data revealed:

• a chord length of 20 m measured from separation provided the most consistent results,
• non-ABS braking affects the results of the critical speed formula, whereas ABS braking provides similar results as non-braked vehicles,
• using 20 m chord measurements for the radius and the average braking coefficient of friction overestimated the measured speed at separation by 4.1% +/-6.3% (+/-1 standard deviation) for all non-braking and ABS braking tests,
• using centre of gravity measurements along the curve for the radius and the average braking coefficient of friction underestimated the measured speed at separation by 2.0% +/-5.2% (+/-1 standard deviation) for all non-braking and ABS braking tests, and
• there is a correlation between braking level and striation angle.