The Basic Nature of Vehicle Understeer-Oversteer

This paper gives a comprehensive analysis of vehicle understeer-oversteer, utilizing theoretical and experimental approaches. It departs from the conventional by defining understeer-oversteer in the transient as well as in the steady-state condition under various types of inputs. The relationship between understeer-oversteer and directional and oscillatory stability is stated within this concept. The paper introduces new definitions, based on transient condition analysis, for direct and indirect understeer, directional and oscillatory stability, side-slip velocity, and others. It employs a computer program evolved from the equations of motion, shown in the comprehensive Appendix, to analyze the basic nature of understeer-oversteer. New procedures are outlined for quantitative determination of vehicle understeer and stability. The paper discusses the relationships between understeer, oscillatory stability, and the subjective “feel” of passenger automobiles. Understeer rate and yaw damping are stated to be the major factors controlling vehicle handling characteristics under transient conditions. The paper discusses, in detail, the direct and indirect understeering-oversteering effects produced by individual vehicle design factors.