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This paper is the third part of a series of vehicle tests designed and conducted in order to further the understanding of vehicle handling and responses associated with a tire disablement event. The first two parts were published in SAE 970954 Drag and Steering Effects of Under Inflated and Deflated Tires [1], and SAE 1999-01-0447 Drag and Steering Effects from Tire Tread Belt Separation and Loss [2]. All of the test results included herein are presented in a manner to facilitate direct comparison to the previous test programs. Under inflated or deflated tires are known to cause increased forward drag and lateral steering effects on vehicles. These effects are commonly suggested to be the cause of driver loss of control and subsequent vehicular accidents. The increased drag and induced steering effects of under inflated and deflated tires are frequently an issue in an accident reconstruction.

Tread belt separation and detachment is a common failure mode of radial tires. The accident reconstructionist is frequently asked to evaluate the effect of tread belt separation and detachment relative to the occurrence of an accident. Publications have previously been directed toward defining the effects of rapid tire deflation on vehicle drag and handling. However, little has been written about the singular effect of the loss of the tire tread belt relative to vehicle handling. The loss of a tread belt from a tire may be followed by rapid deflation. The combined separation and detachment event may have similar effects on vehicle handling as a rapid deflation event. To evaluate the effect of the loss of a tread belt without tire deflation, the authors tested tires prepared so that the tread belts could be intentionally separated while driving at speeds between 50 and 75 miles per hour.

The speed change, Delta V, and the PDOF, principal direction of force, on a vehicle in an accident can be taken together to form a useful measure of accident severity. Many studies have correlated the combined effect of these with the statistical probability of an injury of a certain type and severity according to the AIS (abbreviated injury scale). The usefulness of this concept is enhanced by considering the effective Delta V and PDOF at occupant locations in a vehicle by taking into account the effect of the vehicle rotation. The method of calculating the Delta V at the occupant location is presented in this paper.

Vehicle crush deformation and energy equivalence relationships are widely accepted as technical accident reconstruction tools for estimating the change in velocity (Delta-V) during an impact. Delta-V has been accepted as a basis for evaluating damage severity and potential injury severity. Emori, Campbell and McHenry's work led to CRASH derivative type programs which are based upon a relationship between crush magnitude and Delta-V. SMAC derivative type programs utilize these principles while generating a time dependent analysis (simulation) by maintaining a continuous equalization of forces between the vehicles during the impact phase. This paper reviews basic principles and the relationships between Delta-V, kinetic energy, conservation of momentum, and barrier equivalent velocity which must be adhered to while performing this type of analysis. Several examples and frequently seen misunderstandings of these relationships are discussed.

A combination of metal roof passenger vehicles, an open top convertible passenger vehicle and enclosed multiple purpose utility vehicles were subjected to tip-over-the-front-end type pitch-over tests. The resulting roof crush and occupant compartment intrusion are presented in empirical and pictorial format. The tip-over roof crush performance is discussed relative to other recent side-over type rollover literature and to the FMVSS 216 on Roof Crush Resistance for Passenger Cars.

Vehicle accident analysis relies heavily on mathematics and the principles of conservation of energy and momentum and Newton's laws of motion. In order to apply these principles, it is first necessary to know the approximate vehicle motions. The analytical procedure is interactive using a combination of model analysis and computer-aided engineering analysis to determine linear and angular velocities and accelerations. Scale accident scene models combined with aerial photography to enhance realism has been extensively utilized in evaluation, analysis and presentation of vehicular accident reconstructions to non-technical audiences. Slide and video accident animations have been produced directly from aerial photograph enhanced models and have been used successfully in courtroom presentations since the 1970's.