Lewis Hamilton concedes that while he would love to be more competitive, he is happy with how his W04 performed in practice.
Putting in the laps at the Suzuka circuit, Hamilton set the pace in the morning's session but could only manage sixth in the afternoon.
The Mercedes driver made a small mistake on his flying lap on the medium tyres but it cost him tenths and meant he finished with a 1:34.442 - 0.590s short of Seb Vettel's best.
"This track is so beautiful to drive, it's fast and flowing, and our car really does feel good here," said Hamilton.
"But it's also a very unforgiving and challenging circuit; you're always on the limit so the trick is to balance and control that limit.
"I'm happy with where our car is after the first practice sessions today although, of course, we would love to be more competitive.
"We've got some work to do this evening on the tyre management in particular."
As for how he expects to run for the rest of the weekend, the 2008 World Champion isn't making any predictions.
"It's too early to think about what we can achieve but I'm looking forward to a competitive qualifying tomorrow and then we will have to see what we can do in the race."
The Brit, though, admits he has a few concerns.
"We just did the long run but I don't have any feedback of how I am compared to the others," Hamilton said.
"It didn't feel too bad to me but the rear tyres became a bit of a problem and the Red Bull flew past me so that didn't look too good."
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