NASCAR will use track-specific rules packages at three more race tracks as the sanctioning body continues to try to improve the racing.
A unique rules package had already been announced for Saturday night's race at Kentucky. NASCAR executive Steve O'Donnell said Tuesday a similar low downforce package will be used at Darlington in September.
Teams will use a higher drag rules package at Indianapolis Motor Speedway later this month and Michigan International Speedway in August.
For Indy and Michigan, the aero package will feature a 9-inch spoiler and 1-inch wicker bill; a rear fascia extension panel similar to that currently used for superspeedway events; a 2-inch leading edge on the splitter; and a 43-inch splitter extension panel.