1994-12-01

Evasive Maneuver Capability Without and In the Presence of a Flat Tire 942469

The relatively fragile nature of racing tires, coupled with the inevitable track debris which results from racing accidents, ensures that racing drivers will routinely experience conditions involving flat tire vehicle dynamics. We define flat tire vehicle dynamics as a situation which requires the driver to provide steering and/or braking and acceleration control while the vehicle is running on one or more tires which have dramatically reduced tire pressure.In the present work, we simulate the handling and braking vehicle dynamics which occur in the presence of a single flat tire on the vehicle. The flat tire was simulated via drastically reduced cornering stiffness, partially reduced limiting frictional capability and increased rolling resistance, and was alternatively simulated on both the front and rear axle. No simulations were conducted with more than a single flat tire because multiple tire failures which do not involve an actual accident contact and/or damage are rare. NASCAR vehicle and tire data were used throughout the simulations. No attempt was made to model restraining devices which prevent a flat tire from becoming separated from the rim; all flat tires were assumed to remain in place.A three-degree-of-freedom (3df) handling model employing sideslip, yaw and forward velocity degrees of freedom was used to compute vehicle trajectories and time histories. The model was implemented using the (somewhat restrictive but highly useful) EDSVS software analysis program. Both fixed steering control and active steering control maneuvers were simulated in the form of emergency braking and double-lane-change maneuvers. Vehicle aerodynamic properties (downforce/lift and/or drag) were not included in any of the simulations. Aerodynamic downforce coefficients, drag and lift are known to be extremely strong functions of ride height, pitch angle and yaw angle with respect to direction of travel. It is likely that a flat tire would disturb all three of these highly optimized conditions.Simulation results showed that relatively rich handling and braking maneuvers can still be successfully completed even with a flat tire, and depending upon the axle location of the flat tire. Evasive capability and braking distances, while diminished, still retain modest levels of reserve for all but dramatic maneuvering strategies.

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