Generator failure hurt Bottas's race
Valtteri Bottas's lack of pace in the opening stint of Formula 1's Bahrain Grand Prix was the result of running incorrect tyre pressures because Mercedes generator broke on the grid.
The Finn started on pole position and held the lead at the start but his lack of performance meant he was unable to make a gap and came under intense pressure from Sebastian Vettel, at the head of a queue that included Lewis Hamilton and Red Bull drivers Max Verstappen and Daniel Ricciardo.
"Our generator broke on the grid and we couldn't bleed Valtteri's tyres so we were starting with the completely wrong tyre pressures on his car," said Mercedes chief Toto Wolff.
"We knew he would be struggling.
"[With] Sebastian running second, there is nothing we could have done, and that opened up the opportunity for them to undercut us.
"They did it - they did it quite early and that made them win the race."
Bottas, who ultimately finished third, said the higher tyre pressures made it feel like he was driving on marbles.
"I don't know the exact amount but it was more than one PSI," said Bottas of the extent to which the tyre pressures were wrong for the start.
"Everyone is targeting to be on the Pirelli minimum and that is already too high.
"So everything more than that is worse and worse.
"The effect was basically just felt like a big overheating, it felt like on marbles the rear tyres.
"They were just not working like they are supposed to.
"They are overheating from the surface, from a smaller part of the tyre - you're balance limited and the traction is poor."
After he made his first pitstop, Bottas was able to challenge Vettel for the lead at the restart, but couldn't make it stick, and from there he fell back as he continued to struggle.
However, as his later sets of tyres were pressured correctly, Bottas is unsure why the rest of his race was so difficult.
"Stint two and three, there is no explanation why the rear end wasn't working," he said. "It wasn't normal.
"I was running out of all the tools with the diff and with the brake bias, trying to cure the oversteer.
"When the tyres were new, they were OK, but very quickly when you rise up with the surface temperatures, it gets more and more tricky.
"It was a strange race for me missing so much pace - it's not so easy for me to explain."