The culmination of preseason testing's first week at Circuit de Barcelona – Catalunya saw simulated wet-weather running for tire-supplier Pirelli to get a better gauge on how this year's new, wider tire would perform. The current tires augment the 2017 technical regulations which feature a drastically different and advanced aerodynamic package that is designed to create a higher level of downforce. Tires are now 25 percent wider than they were in 2016, with the front tires increasing to 305 millimeters (12 inches) and the rear tires growing to 405 millimeters (15.9 inches).

A fully soaked track greeted teams as testing began anew at 9 a.m. local time. The Pirelli Cinturato Blue full wet was the tire of choice to start the session, with Haas F1 Team driver Romain Grosjean recording nine laps. But as the sun rose and the track began to dry, teams transitioned to the Cinturato Green intermediate tire. Grosjean ran on intermediates for 26 laps until the track was dry enough for slicks.

With a relatively dry track, Grosjean set out for an eight-lap run on a used set of Pirelli P Zero White medium tires. With less than 10 minutes remaining before the mandatory lunch break, the team bolted four new Red supersoft tires onto the Haas VF-17. Grosjean hit the track for five laps, securing his best time of the morning session on his 49th and final lap – a 1:22.739 that put him second overall, .434 of a second behind Scuderia Ferrari's Kimi Raikkonen.

Water trucks doused the track again during the lunch break, forcing teams back onto the full wet tire to start the afternoon session.

Grosjean knocked out 69 laps in the day's second half, smashing the 56 total laps he earned on Wednesday. And just as he had in the morning session, Grosjean ran through Pirelli's tire lineup as track conditions evolved.

Nine laps were run on the full wet tire with 19 laps on the intermediate. By 4:20 p.m. local time, the track was ready for a return to slicks and the team put four new White mediums on the Haas VF-17. During the swap from intermediates to slicks, Haas F1 Team crew members practiced numerous pit stops, for the car isn't the only component that needs to be ready for the season-opening Australian Grand Prix March 26 in Melbourne.

Riding on slicks for the day's final 100 minutes, Grosjean tried out different setup configurations. His best time of the afternoon turned out to be his best time of the day – a 1:22.309 on his 111th lap with a set of Red supersofts that nicked his best time from the morning session by .430 of a second. The lap put Grosjean fourth among the 10 drivers who participated in the day's test.

Grosjean led the day in laps, tallying 118 tours around the circuit, 25 more than second-best Raikkonen. It marked the second time Haas F1 Team ran the most laps this week in testing, as teammate Kevin Magnussen also ran 118 laps on Tuesday, 10 more than Raikkonen, who ran the second-most laps that day as well.

While Raikkonen was second in the lap count, he was first on the board. He set the day's quickest time with a 1:20.872.

After four days of testing at Barcelona, Haas F1 Team racked up 343 laps for a total of 1,596.665 kilometers (992.122 miles). Magnussen secured 169 of those laps (786.695 kilometers/488.83 miles) on Monday and Tuesday, and Grosjean accounted for 174 laps (809.97 kilometers/503.292 miles) on Wednesday and Thursday.

Romain Grosjean: "It's been a productive day for us. We managed to get some wet running, inter running, pit stop practice, dry running and trying a few setup changes that we had thought about overnight. The car is getting better and better. The team is doing a great job. Our pit stops looked pretty good. We're trying to understand as much as we can. Of course, this is winter testing and it's never going to get close to the conditions we have over a race weekend but, generally, I think we've made some good progress today. Hopefully, we can analyze all of that over the weekend and come back stronger next week."

Guenther Steiner: "Quite a good day today. A lot better than yesterday. We got a lot of data. Romain was able to drive the car for longer stints and get a good feeling for it. We made good progress, even running on the wet, which was not ideal, but we made the best out of it. Now we need to get ready for test number two. Reliability has, obviously, been good. This year we've had very few and very small problems. Compared with last year, it's been a lot better. That is how it should be. Ferrari did a very good job this year with the power unit package. It's been very reliable. The engineers will now go over the data and the comments from the drivers, and out of that we will establish a test plan for next week. We know a lot more about the car now than we did four days ago. Now we can make the next step and hone it out, make it better."

Check out our Thursday gallery from Barcelona, here.