Lewis Hamilton says Barcelona's scorching conditions are a "killer" for drivers but also for tyres, raising fears that more tyre woes may await Mercedes on Sunday.
The current leader of the F1 world championship traded places with teammate Valtteri Bottas at the top of the timesheet on Friday afternoon.
But while Hamilton was happy with his opening day of running, the Briton said the Spanish heat could throw another wrench into the works this weekend.
"It’s definitely quite tough out there, it’s the hottest that it has been," Hamilton said after FP2. practice.
"I don’t think I’ve been to Spain when it’s this hot. We’re here in February and March usually, or early May.
"It’s beautiful weather but it’s a killer in the car and it’s obviously very tough on tyres as well.
"It’s been a good day - the second session was better for me. The long runs we look very close with the Red Bulls so I think it’s going to be a very close race."
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Pirelli has supplied a harder set of compounds in Barcelona compared to last weekend at Silverstone. But the change isn't guaranteed to prevent durability or blistering issues insisted Hamilton.
"I didn't see any blistering, but we didn't see blistering last Friday either," Hamilton said.
"I really can't say too much. It felt OK. We're just about to do a debrief, so I'll find out where we stand in that respect.
"The long run didn't look too bad. I don't know how much further we could go as opposed to how much further Red Bull [can go] compared to us.
"That will define whether or not it's one or two stop this weekend."
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