Don L Ivey

Recent studies to investigate effects of Tire footprint aspect ratio on dynamic hydroplaning speed

Previous National Aeronautics and Space Administration (NASA) Langley aircraft tire friction performance investigations indicated the primary parameter influencing dynamic tire hydroplaning was inflation pressure. The empirical equations derived from aircraft tire test data to estimate tire hydroplaning speed were considered applicable to all pneumatic tires. Some recent studies of several tractor-trailer accidents on flooded highway surfaces, however, suggest that in addition to inflation pressure, truck tire footprint aspect ratio (tread contact area width to length) may significantly effect dynamic hydroplaning speed. Although the truck accident data indicated a new equation to predict highway vehicle dynamic tire hydroplaning speed, collection of additional test data was considered necessary. Tests aimed at obtaining this needed data were initiated by researchers at Texas Transportation Institute (TTI) and NASA Langley. Results from these initial tests using a worn truck tire, an ASTM Specification Standard Tire for Pavement Skid Resistance Tests (E 501) and Specification for Smooth Tread Standard Tire for Special-Purpose Pavement Skid Resistance Tests (E 524) tires are discussed in this paper. The status of the work directed towards developing a new dynamic tire hydroplaning speed equation(s) is reviewed. During wet weather, highway vehicle operators are cautioned to be alert to the possibly lower hydroplaning speeds because of the influence of tire footprint aspect ratio effects when their vehicles are lightly loaded.

Texture, Skid Resistance, and the Stability of Automobiles in Limit Maneuvers

The capability of conventional automobile/tire systems to perform a variety of emergency maneuvers was determined. In general, this capability was quantified in terms of the maximum values of longitudinal and transverse vehicle accelerations that could be produced under specific conditions. These vehicle/tire performance measurements are compared directly with common indicators of available friction such as texture measurements and skid numbers. The texture measurements appear to correlate as well with vehicle performance as do direct friction measurements such as skid numbers and British Pendulum Numbers.