Button: We still lack pace
Jenson Button is expecting a much more competitive McLaren once the season starts, although he concedes that their car still lacks outright performance compared to its rivals.
The former World Champion endured a largely frustrating day on Friday, with his running limited to just 52 laps after a gearbox problem caused him to stop on track during the morning. Button rejoined with about an hour of the session remaining and wound up fifth fastest overall.
Speaking later, he said that in contrast to last year's car, McLaren had a good understanding of the MP4-29, particularly in terms of its likely race performance.
As regards ultimate speed, however, Button said he'd yet to start working on the car's set-up but expressed confidence that upgrades introduced ahead of the Australian GP would stand them in good stead.
"The basic car is good but we're still waiting for upgrades. It definitely has potential, this car, it has a good feel about it," he said.
"We have a very good understanding of the power unit and how to use the ERS under braking but also throughout a race, with fuel usage and what have you.
"Outright pace is something we need to work on. We haven't really done much set-up work because it's been more putting mileage on everything.
"Our last two days is going to be set-up work, so we'll know much more after the last two days."
This year's cars might be more complicated owing to the new technical regulations but after last year's debacle with the unpredictable and slow MP4-28, Button said McLaren had still opted for a more conservative design in some respects.
"I think this car is a good car. But at launch we went in a direction that was for more driveability with the car and it's not just bolt-on downforce that we've got on it, it's usable downforce," he said.
"We always knew we were probably lacking in that area, but we feel that by the first race we'll be good. I don't know where we'll stand but we'll be a lot more competitive.
"I'm not worried about where we are. I'm quite happy with the basic car that we have, but I know we need more downforce. But that's coming."
As for the overall pecking order, Button reckons testing will reveal a more competitive field than many might have anticipated.
"At the last test, I would have said that the Mercedes is very strong on one-lap pace but the Williams was quicker over a race distance; this test, obviously the Mercedes is still as quick as it was and I think the Williams is also," he said.
"But you have the Force India now, which looks competitive and you also have the Red Bull, which looks competitive. You also have the Ferrari, which looks competitive as well.
"There's a lot of cars that are going to be competitive and [the gap between them] is not going to be one-and-a-half seconds. I think the grid's going to be a little bit tighter than we expected.
"Even following Marussia, they look so much better than last year's car.
"I think the grid's going to be a lot tighter than we expect in Australia, which is a good thing."
Red Bull's struggles have been the biggest story of the winter but they enjoyed arguably their best day yet on Thursday, with Daniel Ricciardo third fastest and completing 66 laps in total.
More than 20 of them came in one run at the end of the day and Button, who ran in close company with Ricciardo for several laps, said the Australian's times were around two seconds quicker than his own.
He also reckoned the RB10 looked good in high-speed corners. "When it goes round it will be quick," Button added. "It's just not been going round. He was running a soft tyre and I was running a medium, which makes quite a big difference especially in cooler temperatures, but they're quick.
"If they put a few laps together you can see their pace. It's strong. It's a good-looking car, it looks like it should work.
"If they can complete a race distance then they'll be near the front."