NASCAR Nextel Cup Series
The automobiles' suspension, brakes, and aerodynamic components are selected to tailor the cars to different racetracks. The adjustment of front and rear aerodynamic downforce, spring rates, rear track bar geometry, and brake proportioning are critical to the cornering characteristics of the cars. A car that understeers is said to be "tight", or "pushing," causing the car to keep going up the track with the wheel turned all the way left, while one that oversteers is said to be "loose," causing the back end of the car to slide around which can result in the car spinning out if the driver is not careful. Loose and tight can be adjusted by increasing or decreasing the wedge and adding or removing camber, and air pressure adjustments, all of which change the "footprint" of the tires during cornering. These characteristics are also affected by tire stagger (tires of different circumference at different positions on the car, the right rear being largest to help effect left turns) and tire pressure (softer being "grippier").
NASCAR will mandate changes during the season if one particular car model becomes overly dominant. In fact almost all advantages of using one car over another have been nullified. NASCAR used to mandate stock or stock replacement hoods and deck lids. However, in recent years, NASCAR has begun to require cars to conform to common body templates, regardless of make/model. This is more in-line with recent NASCAR tradition, because none of these stock cars have anything mechanically "stock" about them.