Max Verstappen and Daniel Ricciardo say that have work to do if Red Bull is to challenge Mercedes and Ferrari in this weekend's Abu Dhabi Grand Prix.
The Dutch driver was third fastest in FP1 and just 0.148s off the top time of the session set by Sebastian Vettel. But he lost ground in the evening session where he was sixth and over a second off Lewis Hamilton's best lap.
“The first practice was all right," he said. "But the second less so - probably because we changed so things I wasn’t happy with.
“We tried a few different things today to see what suited the conditions," he continued. "We know what was changed which resulted in me not being able to turn as well as I would have liked, so we should be able to fix that for tomorrow."
Verstappen was one of many drivers to drift wide and run off the track during practice. However he felt there was nothing to worry about.
"The track is pretty slippery, if you run off-line, clip some kerb or find a sandy patch it is easy to lose grip. I think that is why we have seen a few mistakes.
"But that’s what practice sessions are for," he pointed out. "We now know what works and doesn’t work so we’ll adjust things for tomorrow.
"We have to improve as we’re not fast enough to challenge for the win," he admitted. "I’m not happy yet with the balance.
"The engine we had today was an old one," he added. "It is definitely not 100 per cent. We will change that tomorrow to improve the power. With a new engine and an improvement in the setup I am confident we will be in a good position.
"Hopefully we can be closer in qualifying. Usually we should then be even closer in the race," he said. "Mercedes are still looking like the team to beat, as they have been all year. We will try to get as close as we can.”
Verstappen's team mate Daniel Ricciardo finished the day third fastest and felt it had been a pretty good Friday.
"This afternoon we put everything in the car that we needed and it was solid," he said. "On low fuel we looked quite strong. But I thought we would be a bit quicker with high fuel, so we still need to find a bit there.
"The general grip wasn’t quite there and I was sliding around. We’ll try and find a way to keep the tyres working a bit better in the night conditions.
"We were ahead of one Ferrari and one Mercedes today [but] we expect them to be quick tomorrow," he added. "If we have the same pace tomorrow as we had today I expect them to jump us. We still need to find a bit more speed.”
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