NASCAR will make more aerodynamic changes to promote improved competition at upcoming races at Michigan and Kentucky.

The changes to the rear spoiler, front splitter and rear deck fin will help NASCAR continue to reduce downforce and sideforce as it attempts to put the handling of the cars back in the hands of the drivers.

NASCAR has been tweaking the package at the request of the drivers, who overwhelmingly favor less downforce. NASCAR made a pair of changes before last week's All-Star race, and the on-track product was improved. The race had a pass for the win in the final segment for the first time in years.

Downforce is the pressure created across the surface of a moving car. Sideforce is generated by the flow of air along the sides.