Romain Grosjean completed a day high 118 laps of the Circuit de Barcelona-Catalunya on Thursday, with the Haas F1 Team driver ending fourth fastest overall.
The Frenchman ran the wet weather compounds before switching to the dry tyres as the pre-wetted track dried out under the Spanish sunshine, and felt the VF-17 has been getting better and better over the four days of testing.
Grosjean will be back in the car on days two and four of next weeks second test at the circuit, hoping that what the team have learned so far translates into further progress.
“It’s been a productive day for us,” said Grosjean. “We managed to get some wet running, inter running, pit stop practice, dry running and trying a few set-up 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 analyse all of that over the weekend and come back stronger next week.”