Jenson Button admitted he was struggling to get the best out of the harder compound Pirelli tyres despite leading the way in Friday practice ahead of the Spanish Grand Prix.
The McLaren driver posted the best lap of 1min 23.909secs in the second session of the day at Catalunya, which was good enough to put him ahead of the Red Bull of defending champion Sebastian Vettel.
Button's best time came on the softer option tyre but he said he wasn't happy with his performance when he then tried the harder tyres, with a bigger gap between the two compounds this weekend than compared to the four previous races this season.
“It was a positive afternoon,” he said. “I did a good lap on the option tyre, the car is running well, and our upgrades seem to be working. But there are still some improvements to be made. The option seems to be a bit easier for everyone as it's softer and therefore more receptive to generating temperature. In P2, we also started to find a way to get the prime to work, but then, later in the session, we couldn't quite get back to that sweet-spot.
“If we can solve these issues with the prime and get it into its correct working range, I think we can be quite competitive this weekend. There are a lot of quick cars out there, but, aerodynamically, I think we've got a strong car. We've just got to make sure that we make sure that the four things touching the road are working properly for us too.”
Team-mate Lewis Hamilton was fourth fastest but despite admitting that the car felt better than in Bahrain, he was struggle to get the best set-up for the conditions.
“The car already feels better than it did at the last race – there's a good series of improvements within the car,” he said. “My long run this afternoon was very satisfying and there are positives to take from that, but there's still more time in the car, as Jenson showed.
“I struggled a little with set-up today. It's a little bit inconsistent, so it's very difficult to pinpoint exactly what's needed to make it better. But we'll be looking at the data to find out where the most significant issues are, and I'm confident we can make improvements overnight.
“Nevertheless, the upgrades we brought to this race seem to be working well and we've got good pace on the longer runs. The guys back at the factory did a fantastic job. It's been a positive day and we're in the fight.”