Eager to add to Patron Highcroft Racing's championship lead, David Brabham set the fastest time in Thursday's test session for the Acura Sports Car Challenge at Mid-Ohio Sports Car Course.
The reigning overall winner from the 24 Hours of Le Mans set a fastest lap of 1min 11.826secs around the 13-turn, 2.25-mile road course to lead the way ahead of fellow Acura runner Gil de Ferran.
Brabham and team-mate Scott Sharp go into the event leading de Ferran and Simon Pagenaud by 13 points in the championship standings.
"The track was really strange,” Brabham said. “When I first got out there my eyeballs nearly jumped out of my head because I couldn't believe how little grip there was out there. This track can do this from time to time. Apparently they had rain a couple of days ago and that washed all the rubber off.
"The difference between a day like today and when things are all rubbered up could be up to four seconds. Everyone was struggling a bit but the guys did a great job to improve things and we ended up quickest. I know we can go quicker tomorrow. There is still a lot more time in it. We would have liked to be even quicker but you never know what the other guys are doing as well."
In LMP2, Lowe's Fernandez Racing team owner Adrian Fernandez was quickest in the Acura ARX-01b that he shares with Luis Diaz. Fernandez was 1.11 seconds quicker than Team Cytosport's Klaus Graf, driving the team's new Porsche RS Spyder.
The team acquired the Porsche from Dyson Racing, who campaigned the car in 2007 and 2008. Dyson's Butch Leitzinger was third quickest in the first of the team's Mazda-powered Lola B09/86 coupes
Dirk Müller went fastest in GT2 for BMW Rahal Letterman Racing Team, with a lap some 0.323secs quicker than Darren Law in the first of the Flying Lizard Porsche. Jorg Bergmeister in the sister car was third.
The new GT2 Corvettes slotted into fifth and sixth in class on their first day of running with the team's new class rivals.
“We didn't really do anything different,” said programme manager Doug Fehan. “Based on the simulations we ran before this week, we had a pretty good idea how the car would react. We made some minor adjustments early and achieved our goals.”
Guy Cosmo was the quickest Challenge class driver for Porsche 911 GT3 Cup entries.