The Take Away on Rollover Drag Factors
Dolly rollover tests suggest that the appropriate drag factor range for use in rollover reconstruction, excluding special circumstance, is 0.38 to 0.50. The finding is from the calculated results of 81 dolly rollover crash tests statistically trimmed to exclude the upper and lower 15 percent.
Reevaluation of roll phase analysis of rollover tests on an actual highway found lowered average roll phase drag factors. The average roll phase drag factor as published in the papers was 0.53 g (min = 0.39, max = 0.74) and the average reevaluated drag factor was 0.45 g (min = 0.36, max = 0.52). Natural rollover tests suggest the appropriate drag factor range, excluding special circumstances, is 0.39 to 0.50. The finding is from the calculated results of 21 naturally occurring rollover crash tests statistically trimmed to exclude the upper and lower 15 percent.
Getting Rollover Drag Factors Right
A comparison was conducted of numerous historical studies by reexamination of the original works, analysis of their data, and centralized compilation and analysis of their results. In total 81 dolly rollover crash tests, 24 naturally occurring rollover crash tests, and 102 reconstructed rollovers were identified. Of the 24 naturally occurring tests 18 were steer induced rollover tests.
The range of drag factors for all examined dolly rollovers was 0.38 g to 0.50 g with the upper and lower 15 percent statistically trimmed. The average drag factor for dolly rollovers was 0.44 g (Standard Deviation = 0.064) with a reported minimum of 0.31 g and a reported maximum of 0.61 g. The range of drag factors for the set of naturally occurring rollovers was 0.39 g to 0.50 g with the upper and lower 15 percent statistically trimmed. The average drag factor for naturally occurring rollovers was 0.44 g (Standard Deviation = 0.063) with a reported minimum of 0.33 g and a reported maximum of 0.57 g.
Reevaluation of roll phase analysis published in two papers reporting results of rollover tests on an actual highway (Asay, 2009 and 2010) found lowered average roll phase drag factors as shown in table 1. The average roll phase drag factor published in the papers was 0.53 g (min = 0.39, max = 0.74) and the average reevaluated drag factor was 0.45 g (min = 0.36, max = 0.52). Reevaluation was performed from data published in the papers. A final analysis should be conducted using the actual test data.
Published results of reconstruction derived roll phase drag factors (Hight, 1972) between 0.40 g and 0.65 g was confirmed as the range representing the middle 60% of pre-1972 reconstructed rollover crashes on flat ground, figure 3. The reconstructed drag factors were in a range of 0.04 g to 1.20 g for all 102 plotted results, including downhill rollovers and rollovers with vertical drops. For rollovers on flat ground the reconstructed range was 0.21 g to 0.83 g.
Will Electronic Stability Control Eliminate Tire Tread Separation Crashes?
By Mark Arndt
Will Electronic Stability Control Eliminate Tire Tread Separation Crashes?
Probably not, but the technology holds great promise to substantially reduce these crashes. Recently published testing results demonstrate that Electronic Stability Control (ESC) systems provide drivers a greater steering margin of safety when their vehicle experience a rear tire tread separation.
The study also found that not all ESC systems are alike in their potential benefit. Some systems provide a greater benefit to the driver in the event of a rear tire tread separation than others.
A rear tire tread separation event can lead to loss of vehicle control as a result of an unexpected deviation to the vehicle’s intended path in combination with significant change that occurs to the vehicle’s steering characteristics. Vehicle designers have had difficulty providing substantial improvements in basic vehicle response after a tire tread separation, but ESC was shown to make a substantial improvement in rear tire failure events (video).
Mark W. Arndt
