Hot temperatures and tyre degradation are set to become key factors in the cliffhanger finish to the IndyCar Series, the Go Pro Grand Prix of Sonoma.
The northern Californian road course venue replaces traditional ovals as the series' closing race which is set to play out over 85-laps and is scheduled to start at 2.07pm on Sunday (local time).
Firestone technicians declared the opening practice session, topped by defending series champ Will Power, had seen the highest temperatures this season on a road course.
The track temperature rose to 54 deg (celsius) at one stage during practice before it dropped to 39 inside the final 60 minutes of the session.
Team Penske is preparing for tricky conditions in qualifying and the race around the 12-turn circuit.
While the champion squad has a brilliant record at Sonoma headlined by Power's three victories over the last five years, it remains on guard about the fluctuating conditions.
“This place is only second to Indy with low grip,” Team Penske technical director Ron Ruzewski told Speedcafe.com.
“The track is very temperature and wind dependant and you can get lost easily if you don't pay attention to it.
“You have to be mindful of the weather and the changes it causes.
“Sand and wind regularly change things. It is abnormally warm here now.”
Several drivers acknowledged the race will come down to tyre choice and strategy.
CLICK HERE to see points standings going into the Sonoma finale