Only Romain Grosjean to run Haas F1 upgrade in Spanish GP practice

Haas has struggled with getting its tyres into the right operating window so far this season, which has especially hurt it in races.

Although it feel it understands what the problem is, team principal Gunther Steiner said Haas does not yet have a solution in place to overcome the issue.

The team has decided to keep Kevin Magnussen in the older specification on Friday while Grosjean runs Haas's major update package, as it wants to avoid confusion over the impact of the new parts on the tyre woes.

"What we are doing tomorrow, we will run one car on the 'old' spec and one on the new spec, so we have something to compare," said Steiner.

"If with the new spec we've got issues at least we can compare it.

"If you put two cars on the new spec and you've got an issue, is it the tyres or the new spec?

"So we've got one and one and then we can convert the second car on Friday night if everything goes to plan.

"We've got all the parts. We consciously wanted to have a back-to-back and not to confuse us more with the tyre issue."

The Haas update includes a new floor, front wing, bargeboard and mirrors.

Steiner reiterated that while the team is making progress in understanding what issues it faces with tyre use, there is not yet a solution in place.

"We know what we need, but we don't know how to get it," he said. "It is as simple as saying that.

"We just need to get in the window by running the tyres warmer. It sounds almost too simplistic, so you could be asking why are you not doing that?

"[The answer is] because we don't know how to get the temperature in the tyre.

"We are not the only ones, but maybe we are affected more than other people, I fully admit that."

With the Barcelona circuit featuring more high energy corners than Baku, Steiner is at least hopeful that his team's form will not be as bad as it was in the last race in Azerbaijan.

"It cannot be worse," he said. "I think Baku was the worst.

"After you have had three races like we have had, you always lose some confidence. It is not like I would say 'we will be fine here'.

"Here, we should be OK. We were OK in testing, we were OK in Australia and now if we are going backwards, it will be like 'what happened?'"