Lewis Hamilton says he is still struggling to drive his Mercedes in the rain a year after joining the team.
Hamilton qualified fifth in the wet for Sunday's Brazilian Grand Prix while team-mate Nico Rosberg will start second.
"The wet sessions haven't been too good this year," said Hamilton, who joined Mercedes after six years at McLaren.
"It's different to the McLaren. I was used to that and knew how to set it up. This car's harder to drive in the wet."
Hamilton has always been regarded as a wet-weather specialist, and two of his greatest wins have come in heavy rain. Victories in Japan in 2007 and Silverstone in 2008 are considered to rank up with the greatest wet-weather drives in history.
But this year Rosberg has generally had the better of Hamilton on a wet track.
"When I was at McLaren I was there for a good period of time," Hamilton said.
"When I went into the first year [in 2007] I had done a lot of simulator running to get the car the way I liked it. And over those next years the car was being built for me - and my team-mate obviously [but] I had a lot of input into that.
"This year's car was built through work with Nico and developed with Michael [Schumacher, who was at Mercedes from 2010-12], who drives different to me.
"So naturally it has been a very difficult year in terms of trying to extract the most from the car.
"So it's actually not such a bad year considering it's been my first year in a car I've not really known.
"But there are still so many things I'm learning even this weekend. There have been lots of problems.
"Nico has been here four years now and the stuff I'm learning is similar to the stuff he was learning three years ago and I'm hoping next year from this year's experience I have a much better understanding."
Rain has been forecast for Sunday's race in Sao Paulo but Hamilton said that "everything's to play for - I'm just going to give it everything I have".
Team boss Ross Brawn said: "We haven't quite got the car to his liking. We are improving and Nico has demonstrated that with his extra experience of the car he can get it dialled in more frequently - and that's where we have to get Lewis.
"It's just a matter of time, I think he has progressed very well this year and it's not something we are overly concerned about. It's something we will definitely improve next year."