Lewis Hamilton says Ferrari has the advantage at this weekend's Russian Grand Prix and has dismissed Sebastian Vettel's suggestions that Mercedes were sandbagging.
Vettel was 0.709s faster than Hamilton in second practice -- the biggest margin between a Ferrari and Mercedes during Friday practice this season. Vettel is convinced Mercedes was not showing its true pace, but Hamilton insists the gap on Friday was as big as it looked on the timesheets.
"We never sandbag, there's no benefit to sandbagging. Ever," he said. "I think Ferrari have done in the past but there is zero benefit for us to do so. We are trying to get the car to the optimum balance-wise and today has generally been a tricky day.
"The Ferraris definitely are quickest, as they have been all year so far, so we will work hard this evening and into tomorrow to try and see if we can pick up some pace."
Part of Hamilton's problem was a series of aborted quick laps on the ultra-soft compound. He twice abandoned a qualifying-style lap after Turn 4 and even when he hooked together two complete laps on the softest compound and low fuel they were far from perfect.
Part of the problem is Sochi's smooth track surface, which can mean it takes several laps to get the tyres up to temperature, but Hamilton believes his issues are could be more general.
"The problem is we can't get them to work on lap one, two, three, four, five at least! Ferrari, after two timed laps, got better and faster in the third and fourth I think. The tyres have just been generally difficult to work here so that's what we've been trying to get working better.
"I was pushing and pushing and pushing trying to get the tyres to operate at their best but we are not quite sure whether or not we are in the window [of performance], and so that was generally how it was with them today. We're going to do some investigating to see if maybe we are in the window, maybe we are just slow. We shall see tomorrow."