Valtteri Bottas is expecting drivers to struggle with tyre degradation on race day given the warm temperatures that will likely surround Paul Ricard.
The Mercedes driver picked up the baton from team mate Lewis Hamilton on Friday afternoon, setting the pace in the day's second free practice session.
"It was not easy in the beginning; everyone struggled in the morning because the track was much more slippery than usual," said Bottas.
"But the track ramped up quickly, I could feel big gains on a lap-by-lap basis, especially in the corners.
"The more the track improved, the better the balance of the car felt. Despite the balance issues, the car was quick out of the box which is always a good start.
"We've made good changes between the sessions and I felt much more comfortable in FP2, which is why the lap time was better."
The scrappy session saw many drivers slip and slide - including Bottas and Hamilton - as a result of poor grip, with Pirelli's soft tyre particularly difficult to manage.
"It's really warm out there, and it will only get warmer, so tyres are going to be on the limit, especially on Sunday.
"We still struggle with the balance over the course of the entire lap, so we'll have a good look at the data tonight to see what we can improve for tomorrow."
Mercedes trackside engineer Andrew Shovlin believes the team's struggle for balance was largely rooted in its W10's rear tyres.
"It's been an interesting day from the point of view of the tyres and the car performance," said Shovlin.
"All the cornering regions of the circuit have been recently resurfaced and it was clear that the soft tyre was suffering quite badly on the new tarmac.
"Our pace looked pretty good, but the balance was really messy due to poor grip from the rear tyres.
We made some changes over the break to help calm the car down and both drivers felt it was better in the afternoon.
"Valtteri had a clean session, his pace on low fuel was good and the long run was consistent.
"Lewis was finding it a bit harder to get the balance of the car in the right place and he made a mistake on his soft tyre run.
"We have a bit of work to do tonight to see if we can further improve the rear end, but we seem to have a decent car to work with. So, overall we are quite happy."
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