Massa: Mercedes still the F1 benchmark despite Williams form

The Brazilian produced a 1m23.500s lap on soft tyres on Thursday, beating Romain Grosjean's best super-soft effort from last week by half a second.

But although encouraged by his pace, Massa reckons that reigning champion Mercedes has yet to show its full potential, having done much of its running on mediums.

"The result was positive, but it is still difficult to be sure where we are, especially compared to Mercedes," said Massa on Thursday evening.

"I still believe Mercedes has the best car, but we are there.

"The car is showing good performance but also good handling, and good understanding."

When asked by AUTOSPORT if he felt the team was closer to Mercedes, Massa said: "I hope! But I think when you are not on the right time, with the same tyres and the right fuel, it is difficult to be sure.

"I still believe when Lewis goes out and does five laps and is very consistent from first to last, even better than us, I still believe they have something in their pocket.

"It is difficult to know where we are compared to them and if we improved compared to the last race, I don't know.

"But if you compare also the other teams, we are there in the fight, and this is important."

Massa believes that Williams should take huge encouragement from its laptime on a track like Barcelona - which puts a premium on downforce.

However, he remains cautious about the consistency of the FW37 over longer race distances.

"This track was not a fantastic track for us looking at last year," he said.

"It is a track that we were struggling, a track where we lost out compared to other cars, because we were missing downforce.

"And I think when you see that, when we wanted the lap time, it was OK.

"I don't know actually to answer 100 per cent if we really made a step.

"But, compared to last year, the car is easy to drive and that is a little bit better, a bit more stable.

"But still we need to work on degradation because it is not low, for many people.

"Maybe not Mercedes, but for many people it is not low. So we need to work to make the car more consistent."