A series of open loop tests was conducted on three vehicles instrumented per SAE J266 to determine the effect of a rear tire tread separation on the vehicles' behaviour. The vehicles tested were a 1989 Ford Bronco II, a 1996 Ford Explorer, and a 1993 Ford Taurus. The tests were categorised as tread separation event tests and tread-separated tests. The tread separation event tests were designed to determine how the vehicle responds as the tread is separating from the tire carcass at speeds ranging from 58-119 km/h (36-74 mph). Tires were prepared in a manner that would initiate either a complete or partial separation of the tread. The vehicle was driven on a straight path with the steering wheel held fixed as the tread came off. The tread-separated tests were run on vehicles where the tread was removed from one of the rear tires. The manoeuvres conducted were circle turns per SAE J266 (constant radius and constant steer) and step steer turns. These tests were run to evaluate the steady state and dynamic oversteer/understeer characteristics of the vehicles. The results of the tread separation event tests demonstrate that the vehicle's response is dependent on speed, duration, and the nature of the separation event. The vehicle responds by pulling to the side of the tread-separating tire. The longer the tread takes to come off, the greater the vehicle response. Once the tread had separated, the vehicle's response to the event ceased. Partial tread separations result in a significant vehicle response due to the continuous duration of the event. Higher speeds result in a greater vehicle response. The tread-separated tests show that the vehicles oversteer when the tread-separated tire is on the outside of the steering manoeuvre resulting in vehicle spinout. The vehicles transition to a steady state oversteer behaviour at lateral acceleration levels of approximately 0.2 g.
Abstract