NASCAR announced it is changing the race package for the Pure Michigan 400 at Michigan global Speedway on August 16.

The first of NASCAR’s track-specific rules packages will debut this weekend at Kentucky Speedway.

All five races with new rules will take place before the 10-race championship Chase, but it is possible more could be added this season.

The lower downforce package, to be used at Kentucky and Darlington (Sept. 6), calls for teams to use a 3.5-inch spoiler instead of a 6-inch one. NASCAR executive Steve O’Donnell said Tuesday a similar low downforce package will be used at Darlington in September. Don’t expect to see a big tire change at Kentucky as Goodyear did not create a tire specifically built for Kentucky the way it did for Darlington. “I think we we’re looking at over 200 (mph) before, and kind of the 191 range that we’d be looking at now”. That package will include nine-inch spoilers with one-inch wicker bills, rear fascia extension panels similar to those used on superspeedways, two-inch leading edges on splitters, and 43-inch splitter extension panels.

“Obviously, we want to wait to see what happens at each of these events”, he said.

The current aerodynamic setup makes it hard to pass the race leader, as cars without turbulent air around them (like the lead car) go faster.

Cup teams have two test sessions planned Wednesday afternoon at Kentucky to prepare for the new package.