Felipe Massa says Williams still cannot pinpoint the reasons for the FW37's lack of pace in wet conditions.
Both Massa and his team-mate Valtteri Bottas stormed to the front of the British Grand Prix on Sunday, managing to put Mercedes under severe pressure. However, when the rain began to fall at Silverstone, both drivers lost time which ultimately cost the team a podium in their home grand prix.
Massa and Bottas finished in fourth and fifth respectively, with Massa over 11 seconds behind Sebastian Vettel, who claimed the final podium position on the day.
Massa stated that the problem, which can cost the Williams drivers up to two seconds a lap when compared to other front-runners, had been ongoing since he joined the team in 2014.
"For sure we have a problem. Since two years ago we are trying to understand why we are not quick in the rain, which is not nice. We have a problem, if you see the difference in lap times we were maybe fighting with Mercedes, they were 0.1 or 0.2s quicker than us in free air, not more than that. In the rain we were maybe two seconds," he said.
Although Williams have tried to identify the cause for their lack of pace in the wet, the problem had yet to be isolated.
In 2014 the Williams FW36 also suffered from similar complications in wet conditions.
Massa continued: "We have been trying to understand it for two years! I don't know. If you see our car this year is like an evolution of the car from last year. Last year was very bad in the rain and this year also, so we don't know yet.
"We have been trying to analyse it for a long time but we didn't find out yet. We just lose a lot of grip, it looks like something is going on, something is happening."