Impound race (NASCAR)

An impound race in NASCAR is a competition format where teams are restricted from making significant changes to their cars after qualifying. Once a car passes post-qualifying inspection, it is essentially "impounded" by NASCAR. Teams are typically limited to minor adjustments, such as air pressure adjustments, minor spring rubber changes, and fuel fills. The primary goal of impound races is to reduce the competitive advantage of teams with superior resources or engineering capabilities, theoretically leveling the playing field by preventing extensive overnight work on the cars.

The impound rules typically remain in effect until the start of the race. Once the race begins, normal rules regarding repairs and adjustments during pit stops apply. This means teams can make more substantial changes to the car based on the handling characteristics they experience during the race.

Impound races are often used at tracks where aerodynamic performance is critical and where overnight development would likely produce a noticeable performance gain. The practice has become less common as NASCAR has evolved its inspection and penalty systems to curtail excessive post-qualifying alterations. The rules for what constitutes an impound race, and the allowable modifications, can vary depending on the specific NASCAR series (Cup, Xfinity, Truck) and the track.