Lewis Hamilton has said his car is "feeling good" and he was pleased that he was able to build a "solid platform" on the opening day in Austin, Texas.
The Brit topped both practice sessions at the Circuit of The Americas and beat his own track record in the process.
"It's been an interesting day with lots of ups and downs in terms of how the track has moved around and how the car feels, but overall the car was feeling good," said Hamilton.
"There are lots of areas we can improve on, but generally it feels like a solid platform and a solid start."
Hamilton's team-mate Valtteri Bottas, meanwhile, recovered somewhat from a scrappy FP1 session and finished sixth tenths off the pace in P4 after FP2.
"In second practice we got a lot of running done, both short runs and long runs," Bottas said.
"In the end, we got everything from today that we needed.
"Setup-wise, I think we have the usual work to do. Overall, it has been a pretty normal day. I enjoyed it, but I'm hoping there is more to come tomorrow."