Although it appears McLaren have taken a step forward in China, Jenson Button fears it is not as big as the team had expected.
McLaren arrived in Shanghai with various updates for their MP4-28 including a revised rear that is not as aggressive as its predecessor.
Button finished Friday's running sixth on the timesheets with a 1:36.432, which put him 1.092s off the pace.
"We can't yet conclusively tell if the upgrades we brought to this race have improved the car," said the 2009 World Champion.
"They're perhaps not as big a step forward as we'd expected - the issues with the car are still there - but the car does feel a little bit better.
"We've worked very hard over the last few weeks to bring the new parts here - which is great.
"Today's been all about putting mileage on those parts; now we need to sit down and look at the data this evening - there's a lot to look through."
The Brit weighed in on Pirelli's tyre choice for the weekend, revealing that the pace with the soft tyres drops off after just one lap.
"I feel we'll be using the Prime tyre quite a lot in the race. The Option tyre transforms the car completely; over one lap, there's a lot more grip, but then you start to lose time over each successive lap."
The tyres also caused the McLaren driver a minor problem when his front left delaminated 15 minutes before the end of FP2.
"My puncture happened after I'd already decided to pit. I got to the braking zone at Turn 14, locked up the front left and the tyre just punctured - there was a hole through it.
"It's a good job that corner is just before the pits. I don't think we'll be fighting at the front this weekend, but we'll definitely be fighting someone."