SAKHIR, Bahrain -- Kimi Raikkonen topped the second practice session for the Bahrain Grand Prix as Ferrari emerged as the fastest team under the floodlights on Friday evening.
Raikkonen was 0.11s clear of teammate Sebastian Vettel at the top of the timesheets and over 0.5s faster than the two Mercedes drivers. Raikkonen hooked up a relatively clean lap compared to his rivals to set a 1:29.817, but saw his session come to an early end when a long run was interrupted by a loose wheel nut following a practice pit stop. The unsafe release from the pits will be investigated after the session and will likely result in a fine.
Valtteri Bottas was 0.563s off Raikkonen's best lap and 0.092s clear of his Mercedes teammate Lewis Hamilton. Bottas appeared to hook up a clean lap, but Hamilton came across traffic on both his attempts, losing time on the faster of his two runs behind a Haas in the final corner. Red Bull also struggled to show their true potential after Max Verstappen complained about a lack of power on the straights following his quick lap and Daniel Ricciardo was blocked by a slow-moving Bottas at Turn 4 on his hot lap.
Mercedes boss Toto Wolff believed part of the gap could be explained by Ferrari experimenting with more powerful engine modes.
"They were in a pretty high-power mode when they were on the lap, so it isn't so worrying, but it is a good lap," Wolff told Sky Sports. "And what we have seen in Melbourne and again here is that at various stages the teams are close together, so I can't really judge.
"It's quite amazing. We have GPS data, so you can follow the traces of every car. You can see that when you overlay the data, suddenly on the straights they gain much more time, and in the corners it's still the same.
"You can see that in detail, so it's become very transparent for the engineers how much somebody has turned up the power, and how much downforce, and how much drag everyone is running."
Nico Hulkenberg was seventh fastest as F1's midfield looks set for another close battle this weekend. The Renault driver was just 0.012s clear of Toro Rosso's Pierre Gasly, who looks surprisingly quick in the Honda-powered STR13 this weekend. Fernando Alonso was another 0.050s off the pace in ninth and was the fastest of the two McLarens, 0.140s ahead of teammate Stoffel Vandoorne.
Haas' Romain Grosjean finished the session 11th fastest -- 1.774s off Raikkonen's pace but ahead of the second Renault of Carlos Sainz and the two Force Indias of Esteban Ocon and Sergio Perez. Kevin Magnussen was 15th fastest after another difficult session behind the wheel of his Haas.
Sauber's Charles Leclerc was 16th fastest ahead of the two Williams drivers and teammate Marcus Ericsson. Brendon Hartley was at the bottom of the timeseheets in the second Toro Rosso with a time 1.676s off teammate Gasly.