Lewis Hamilton thought Mercedes F1 testing plan was 'crazy'

Hamilton completed 99 laps on his final run of this week's test at Barcelona's Circuit de Catalunya before handing over to team-mate Nico Rosberg for the afternoon session.

Over his three stints - effectively two full days - in the F1 W07 Hybrid, the reigning champion amassed a total of 343 laps, or 1,596km.

That was the target set by Mercedes for both its drivers ahead of the four days, which Hamilton did not feel was possible beforehand.

"It's been a tough week, we've done a lot of mileage, said Hamilton.

"It's been the best week of testing we've ever had.

"Before we came here the team talked about doing 800 kilometres per day, and I was thinking they were crazy.

"I've never done that in the past, and usually the car breaks down.

"But I've never had a test like this where the car just goes on and on and on.

"It's been a physical challenge doing all the laps, but it's just been incredible.

"I've never seen anything like it, just the strength of this car overall."

Hamilton also feels proud at the fact the team has not rested on its laurels over the winter after clinching back-to-back world titles.

"To think we've won two world championships, and going into our third year you would think it's so easy for us to lose focus," added Hamilton.

"But everyone is more focused than ever before and they have done an even better job in terms of developing the whole package than they ever have before.

"I hope we keep going from strength to strength."

To date, Mercedes has yet to use any of three different soft-tyre compounds, so the car's true performance has yet to be revealed.

Hamilton, though, does not feel that will be in question as he said: "We don't know the pace of the car yet.

"What we can say is it's going to go the distance, and that's half the battle, but I don't think it's slow."

For now, a new front wing tested on Friday appears to be paying dividends.

"The front wing is an improvement, which is good," he said.

"It's what we hope for, small increments, and that's what it's brought."