Jenson Button baffled by hard tyres in Spanish Grand Prix practice

The McLaren driver set the pace in the afternoon session, posting the quickest time thanks to a run on the soft Pirelli compound.

When running on the hards, however, Button admitted he was finding it impossible to get them working properly despite the high track temperatures.

"It was a good afternoon, but a tough one, trying to understand the tyres," said Button. "And we still don't quite understand them, but the car seems to be work well on the soft tyres.

"On the hard tyre I just can't get it working. I just can't get the temperature into the tyres. I don't know why it is but it's something we need to sort out for Sunday."

Button admitted the gap between the two compounds brought to Spain was huge for him.

"For me it felt massive, but for other people... For Lewis [Hamilton], he seemed quicker on the prime than he was on the option, and I was the other way around, so it's a strange one," he said.

"It's normally the other way around for me, so the prime would normally be a good tyre for me. Hopefully we can figure it out."

Hamilton, meanwhile, said he had not enjoyed a great day after struggling with the set-up of his car, which made the balance very inconsistent.

The Briton was fourth quickest.

"I still smile, but it's not been a great day," said Hamilton. "We struggled a little bit with the set-up, but the upgrades have worked pretty well. We have good pace, in particular in the longer runs.

"We are in the fight, at least, but we didn't really show it because we had a bit of an inconsistent set-up today, which means it's very difficult to pinpoint exactly what I need to do to change the set-up to make it better. We need to look at the data and try to find where the most serious issues are and try to correct that for tomorrow.

"The balance is very inconsistent so it's very difficult to pinpoint exactly what we need to change to make it better."

Hamilton said, however, that the upgrades introduced by McLaren were already making the car stronger.

"The car already feels better than it did in the last race and we are still trying to work on managing our tyres," he said.