Valtteri Bottas is cautiously optimistic of his and Mercedes chances at this weekend’s Formula 1 Hungarian Grand Prix after a solid showing on Friday.

The Finn topped the second hour of practice on the opening day, narrowly heading team-mate Lewis Hamilton after the duo had trailed Max Verstappen in Free Practice 1.

While the Red Bull driver struggled with understeer, changes between sessions saw improvements for the Mercedes duo.

“Recently we’ve been making improvements and I don’t think we’re in too bad a place but it’s only practice, you never know what teams are holding back,” Bottas explained.

“In FP1 we had work to do with the balance but we made changes quickly and were in better shape for FP2, and no doubt there’s still more to come.”

Hot conditions saw most struggle for grip, with the soft and medium compound tyres favoured through practice.

Forecasts predict rain for Saturday, and potentially thunder storms, with Sunday set to be overcast and temperatures in the low 30s.

“To see Valtteri and I at the top of the timesheets this afternoon is pleasing, it’s great for the team and we’ll only improve on that,” said Hamilton.

“We have some work to do tonight to see how we can finesse the car some more.

“You can’t plan for the rain, it’s so unpredictable so you just try and get the car in the best place, understand the tyres, and set the car up for a dry Qualifying and if it rains, it rains,” he added.

“I’m optimistic because I definitely think we can improve the car balance-wise and if we can do that, we should be there ready to fight tomorrow and for the race on Sunday.”

Andrew Shovlin, Mercedes’ trackside engineering director, added: “We got off to a fairly difficult start on the hard tyre this morning as the grip and balance just weren’t there.

“As the day went on we seemed to improve in terms of the timesheets, although we’re still finding the balance quite tricky.

“It may be that it’s the same for everyone, the track is at 60 degrees (Celsius) after all and the tyres are getting really hot which is making the long runs quite difficult.

“Overall, it is encouraging to see both cars at the top of the timesheets but with a risk of rain it may be a very difficult challenge tomorrow so we cannot take anything for granted.”

Track action in Hungary continues with Free Practice 3 starting at 20:00 AEST this evening.