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084f2db8c6 D. Understeer and oversteer are formally defined using the gradient K: if K is positive, the vehicle shows understeer; if K is negative, the vehicle shows oversteer; if K is zero, the vehicle is neutral. When an understeer vehicle is taken to the grip limit of the tires, where it is no longer possible to increase lateral acceleration, the vehicle will follow a path with a radius larger than intended. Understeer gradient is one of the main measures for characterizing steady-state cornering behavior. Although the vehicle is unstable in open-loop control, a skilled driver can maintain control past the point of instability with counter-steering, and/or correct use of the throttle or even brakes; this can be referred to as drifting. Simply put, oversteer is what occurs when a car turns (steers) by more than (over) the amount commanded by the driver. Vehicle dynamics terminology. These individual contributions can be identified analytically or by measurement in a Bundorf analysis. Understeer: the car does not turn enough and leaves the road Oversteer: the car turns more sharply than intended and could get into a spin . Car and motorsport enthusiasts often use the terminology more generally in magazines and blogs to describe vehicle response to steering in all kinds of maneuvers.
Vehicles are inherently nonlinear systems, and it is normal for K to vary over the range of testing. Contributions to understeer. 2008-01-24 ^ International Organization for Standardization, "Road vehicles Vehicle dynamics and road-holding ability Vocabulary", ISO Standard 8855, Rev. Understeer and oversteer are vehicle dynamics terms used to describe the sensitivity of a vehicle to steering. Limit conditions. Automotive engineers define understeer and oversteer based on changes in steering angle associated with changes in lateral acceleration over a sequence of steady-state circular turning tests. Standard terminology used to describe understeer and oversteer are defined by the Society of Automotive Engineers (SAE) in document J670 and by the International Organization for Standardization (ISO) in document 8855. By these terms, understeer and oversteer are based on differences in steady-state conditions where the vehicle is following a constant-radius path at a constant speed with a constant steering wheel angle, on a flat and level surface. It is involved in other properties such as characteristic speed (the speed for an understeer vehicle where the steer angle needed to negotiate a turn is twice the Ackerman angle), lateral acceleration gain (g's/deg), yaw velocity gain (1/s), and critical speed (the speed where an oversteer vehicle has infinite lateral acceleration gain). References.