Felipe Massa says Williams must understand why it struggles for pace in wet weather, following its showing at the British Grand Prix.
Massa led team-mate Valtteri Bottas during the dry opening stages of the race at Silverstone but, having slipped behind Lewis Hamilton following the pit stop phase, both drivers were left helpless to defend against Nico Rosberg when wet weather struck the circuit.
Massa dropped behind Sebastian Vettel and finished fourth, 36 seconds behind Hamilton, while Bottas narrowly fended off Daniil Kvyat for fifth.
With Williams having struggled in the wet since the start of 2014, Massa says the squad needs to identify the reasons for its lack of pace.
"Our car was so slow in the race, even in that moment when it was still damp in some places, Ferrari was much quicker than us and even in some laps they were maybe more than two seconds quicker than us," he said.
"For sure we have a problem as for two years we’ve been trying to understand why we are not quick in the rain, which is not nice.
"We have a problem – if you see on the lap times [in the dry] maybe fighting with Mercedes, they were one or two tenths quicker in the free air, in the rain we were maybe two second [behind]."
When pressed further for a reason, Massa suggested that the evolution of the FW37 from 2014's FW36 does not help the issue.
"We are trying to understand for two years! I don’t know. If you see last year our car from this year is like an evolution from last year and last year it was very bad in the rain and this year also.
"We are trying to analyse for a long time but we didn’t find it but we just lose a lot of grip and looks like something is going on, something is happening."