Editing Understeer and oversteer (section)

===Test to determine understeer gradient===
Several tests can be used to determine understeer gradient: constant radius (repeat tests at different speeds), constant speed (repeat tests with different steering angles), or constant steer (repeat tests at different speeds). Formal descriptions of these three kinds of testing are provided by ISO.<ref name="ISO_4138">International Organization for Standardization, "Passenger cars&nbsp;– Steady-state circular driving behaviour&nbsp;– Open-loop test methods", ISO Standard 4138</ref> Gillespie goes into some detail on two of the measurement methods.<ref name="fvd">T. D. Gillespie, "Fundamentals of Vehicle Dynamics", Society of Automotive Engineers, Inc., Warrendale, PA, 1992. pp 226–230</ref>

Results depend on the type of test, so simply giving a deg/g value is not sufficient; it is also necessary to indicate the type of procedure used to measure the gradient.

Vehicles are inherently [[nonlinear system]]s, and it is normal for U to vary over the range of testing. It is possible for a vehicle to show understeer in some conditions and oversteer in others. Therefore, it is necessary to specify the speed and lateral acceleration whenever reporting understeer/oversteer characteristics.