Felipe Massa revealed that his pace on Friday in free practice for the Spanish Grand Prix had been hampered by overheating tyres.
Massa was ninth fastest in the afternoon session, albeit 1.2s slower than the fastest time set by Lewis Hamilton. That was an improvement on the morning run where he was only 14th on the timing screens by lunchtime.
"The medium and the hard tyres were quite tricky to run," Massa said after the day's track action concluded.
"We did struggle with them a bit, especially with overheating," he said. "But many others were struggling to make these tyres work too, so it’s not so bad.
"On the whole it was quite a positive day," he added. "The session was a good one I would say."
"Felipe set a good pace, which looks competitive," said Williams' chief technical officer Paddy Lowe. "We gathered all the data that we needed today and we had no problems.
"The medium tyre has proved to be a difficult tyre to work with, both in pre-season testing and in Bahrain."
Massa's team mate Lance Stroll also struggled with the tyres at the Circuit de Barcelona-Catalunya.
"I didn’t get the medium working very well," he said. "It was particularly difficult to find grip and stability in the car.
"It was quite easy to miss corners, have snaps and make mistakes, especially when you lose the temperatures in the tyres.
"I made a mistake on my first lap on the softs, then did two more laps and I finally did a lap time, but the tyre was gone at the end.
"A tough day for me just putting everything together and getting everything to work," he said in summary. "Not the end of the world, as it is only practice."
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