Drag and Steering Effects from Tire Tread Belt Separation and Loss

Tread belt separation and detachment is a common fail ure mode of radial tires. The accident reconstructionist is frequently asked to evaluate the effect of tread belt sepa ration 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 initial phase of the test was conducted at the Transportation Research Center (TRC) in East Liberty, Ohio on the Vehicle Dynamics Area track. The track contains a figure 8 with banked turns. The long straightaway in the center traverses a rectangular, level skid pad. The test vehicle was a 1993 Ford Taurus four door sedan. The tires were size P205/65R15. Twelve tires were tested on the TRC track. Three were tested at each wheel position. Nine tread belt detachments were produced on a straightaway. Three detachments were in curves or during a driver induced steering maneuver. The tread detachments occurred at speeds between 50 and 75 miles per hour. All tread belts separated in one continuous piece, with two or three small fragments in some cases. All of the authors were involved as test drivers and passengers to introduce a range of driver skills and responses. The vehicle speed, forward and lateral acceleration rates, and the driver induced steering torque was measured and recorded. The tests were all videotaped with an in-vehicle camera. All but one of the tests was videotaped from a chase vehicle. The tests that occurred on the straightaway were also videotaped from a station ary camera. Separate tests were conducted to obtain comparative drag and lateral steering effects for intact and inflated tires, and for deflated tires with the tread belt in place. The sequence was repeated for tires with the tread belt detached. These tests were conducted in accordance with the test protocol defined in SAE970954 "Drag and Steering Effects of Under Inflated and Deflated Tires