Skid-Pan

A skidpad or skidpan is a circular area of flat pavement used for various tests of a car's handling. The most common skidpad use is testing lateral acceleration, measured in g. This usage is similar to that of a kick plate.

The test is carried out on a circular track with a defined radius. A car driving on said track is slowly accelerated until the outermost tires on the car begin to slip. Going any faster would cause the car to drive outside the defined radius. At this point, the speed of the car is recorded, and given the centripetal acceleration formula, v²/r, a car's handling in terms of lateral gs can be derived.

...
Wikipedia