First Practice :

As teams and drivers looked to approach the limit on the rough streets of downtown Detroit, 11 out of the 22 cars in the field slipped down into the runoff areas at least once.

Two of those cars were the No. 40 WTR Cadillac and the No. 9 Pfaff Motorsports Lamborghini Huracan GT3, which brought out a red flag after Louis Deletraz and Andrea Caldarelli went off simultaneously into the escape road at the end of Franklin Street.
Both cars were eventually able to continue with the rest of their session, but they will also lose their fastest lap in qualifying later today for causing a red flag in practice.

The two Pratt Miller Motorsports Chevrolet Corvette Z06 GT3.Rs led the GTD PRO class. A string of fastest laps from the No. 3 Corvette of Alexander Sims put him at the top of the table with a 1m10.818s.
He went 0.2s ahead of the sister No. 4 Corvette of Nicky Catsburg, who turned in a best lap of 1m11.009s

Marco Mapelli was third fastest in the aforementioned No. 9 Pfaff Lamborghini, just a few thousandths up on championship leader Laurin Heinrich in the No. 77 AO Racing Porsche 911 GT3 R in fourth; Sebastian Priaulx in the No. 64 Ford Multimatic Motorsports Mustang GT3 rounded out the top five in GTD PRO.

UP NEXT: Practice 2 begins at 11:30am ET.

RESULTS