Paul di Resta has blamed the deficit to his Force India teammate Adrian Sutil on an unexplained top speed disadvantage during Brazilian Grand Prix qualifying.
The British driver qualified 11th after setting a Q2 time 0.3sec slower than Sutil, who has been on impressive form all weekend, but is certain that he has a similar level of pace when the disadvantage is taken into account.
Di Resta was slower than Sutil in every speed trap, averaging 1mph slower using data gathered by the speed traps at the two intermediate points and the start/finish line.
"We've had a delta on the top speed that we can't get to the bottom of," di Resta said. "We are down on the straights and losing a lot of time. That's where all of the time [difference] is.
"We have tried plenty of things. It's a different engine, a different gearbox and there are many different components on the car from yesterday, so you can't blame those. It just seems to have been there since yesterday and it has carried over. It's free lap time."
Despite the problem, di Resta is optimistic of being able to fight for points in Sunday's race.
"The positive thing is that the long runs have been very strong so whether it's a dry race or a wet race, we can be quite confident," he said. "The car seems to have worked well in wet races and the tire wear seems to be under control."