Ferrari's Sebastian Vettel, also a four-times champion and last year's runner-up to Hamilton, has already said that Hamilton and Mercedes will be favourites when the season starts in Australia on March 25.
Here's our guide to pre-season testing.
Noikeee: It was a giant anomaly, it never snows at the track.
Bottas knows he has to be consistently at the top of his game this year, with Hamilton gunning to become only the third driver to win five world titles.
Alonso was fifth fastest, 1.6secs slower than Hamilton, using the super-soft tyre.
"If I achieve them, there will certainly be no problem with the contracts". These teams all have supercomputers which do all the heavy lifting with regards to set-ups and simulations. The Belgian posted a 1m19.854s on the hypersofts and also managed 110 laps as he spent the majority of the day in the car, handing over to Fernando Alonso just after 3 p.m. local time.
Two of Hamilton's last three world championships were internal battles fought against team-mate Nico Rosberg, before last season saw Ferrari offer an increased threat.
Pierre Gasly's Honda-powered Toro Rosso led the lap charts with 147. "It has nothing to do with Valtteri".
El Manchester United ganó, pero sigue muy lejos del City de Agüero
Crystal Palace vs Manchester United se enfrentarán hoy con la necesidad de sumar tres puntos en la Premier League . Con el triunfo, el United recupera la segunda posición que había perdido provisionalmente a manos del Liverpool .
What are the main changes this season? "But then again, so am I". I'd assume so and he's going to be in the best shape possible.
"To be honest though it's not that important in the first week". What is less clear is what is going on at Red Bull, with Verstappen having very little running, and then going off at turn 12, bringing out the second red flag of the day as the Red Bull was recovered. Sure, Hamilton ended the test on top with a lap set on the medium compound, the hardest tire used by anyone on their fastest lap, but the fuel level has to be considered.
"So over the next days, I guess next week, we'll get a better understanding".
"That's where the character of a circuit is".
The circuit has acted as the home of the Spanish Grand Prix since 1991 and has emerged as Formula 1's exclusive pre-season testing venue across the past few years.
Who is the favourite for the title? It was a much-needed recovery for the team despite Wednesday's weather, with reliability issues on Monday and Tuesday seeing it finish with a total of 260 laps for the week. "It's been the first time that I've really been out to learn a lot more about the car and its characteristics".
"This week we've seen the first glimpse of the Renault R.S.18's potential on track, albeit in very cold, wet and unrepresentative conditions", said Abiteboul.
AS for Wolff, he expects Bottas to challenge Hamilton in 2018.