Haas was an unexpected presence among the top tier runners in the second week of pre-season testing, but team boss Guenther Steiner isn't surprised by the team's step up in performance.
Kevin Magnussen was second in Thursday's session behind the unassailable Ferrari of Sebastian Vettel, and Romain Grosjean upheld Haas' form on Friday, concluding his day of work to end up 1.2s adrift of Kimi Raikkonen.
According to Steiner, the US outfit's significant progress is linked to the team's better understanding of its tyres, a weak point during last year's campaign.
"We got [the tyres] to work," Steiner told Formula1.com on Friday in Barcelona.
"We aren't using any hypersofts here. We got them to work on all [the other compounds]. The ultrasofts, everyone seemed to have the same problem.
"Nobody really goes from the supersofts to the ultrasofts any faster. But we tried it now, and the conditions here from 11:30 onwards don’t go rapidly down, it's just warming up.
"We worked on the ultrasofts now and we got a little bit more understanding. All in all, we're pretty okay."
While getting a hold on tyre management will likely boost Haas' performance, Steiner insisted its VF-18 chassis will require a fair amount of work before it is rolled out onto the Melbourne grid in two weeks.
"There have not been many [updates], we’ve got a few bits and pieces," he said.
"We had a few reliability issues with body parts in the first days. We need to fix them and that will already be an upgrade to what we are running now, as we are currently a little bit compromised.
"We'll get that all fixed and then add a few parts that we had planned from before."
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Before the long haul to Australia, Steiner isn't making any bold predictions about the grid's pecking order, whether it's the front of the field or Haas' own mid-field turf.
"The top three? I think up to now Mercedes was a little bit ahead, but again, it's not all done yet," he says.
"They are very close as well. Red Bull picked up and the Ferrari is not bad. This morning they were really good and yesterday, so I think it will hopefully be very interesting.
"[The midfield] will be much of the same it looks like. Because it's so close, it's difficult to estimate at the moment. We'll just find out in Australia."
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