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In the final 15 minutes of the 50-minute session, Reddick posted the top average speed (92.988 mph) in a group of cars that went out on new tires.
Kyle Larson ended up second-fastest (92.618 mph) and Ross Chastain – who won this race a year ago – was third (92.519 mph).
Kyle Busch was fourth and Chastain’s Trackhouse Racing teammate, Daniel Suarez, rounded out the top-five.
Completing the top-10 were Austin Cindric, Michael McDowell, Bubba Wallace, Jordan Taylor (substituting for Chase Elliott) and Ty Gibbs.
Reddick and Gibbs were the only drivers to run at least 10 consecutive laps, with Reddick coming away with the faster average speed (90.267 mph).
Friday’s practice was the first time Cup cars have been on a road course since NASCAR debuted its new aero rules this season for road courses and a majority of tracks measuring 1.058-mile or less in distance.
The package, which was tested in the offseason at Phoenix, consists of a 2-inch spoiler and the removal of three diffuser strakes and engine panel strakes. The changes are to lead to a 30-percent reduction in downforce.
Outside of Taylor, most of the non-Cup Series regulars participating this weekend did not fare so well in practice.
Former Formula 1 champion Jenson Button was 28th-fastest, former F1 champ Kimi Raikkonen was 32nd, Jimmie Johnson was 36th and IndyCar driver Connor Daly was last, in 39th.
About 24 minutes into the session, a caution was displayed for debris in the area of Turn 6.
Chastain went off course briefly in the final minutes in Turn 19 but was able to continue without any issues.