Vettel not judging Red Bull updates yet despite setting pace in practice for European GP

The reigning champion team has brought a substantial package of revisions to Spain, featuring upgrades to the RB8's front wing, floor, sidepods, front suspension and diffuser.

But despite going quickest, Vettel felt conditions were not conducive to a proper assessment of the new parts.

"We have some new bits, but lap times are not allowing us to have a fair conclusion yet," he said. "For us it was important to have a clean practice, a clean day today with no trouble and no problems.

"I am quite happy with what we did. I think conditions might change quite a bit until Sunday - again it was surprisingly cool today. Sunday will be quite a bit hotter which could make a difference, but now we collecting some good data and we'll see now whether we made a step or not."

Vettel's team-mate Mark Webber was ninth quickest, and reckoned he had not had chance to show his ultimate pace.

"You get one lap or two laps on the softer tyre so we didn't do a good job on the soft at all," he said. "So a frustrating finish to the session and plenty to go here tonight."

The Australian was also pessimistic about his race chances, but felt Red Bull knew how to solve his issues.

"[Race pace is] not very good, but we know where we can improve," Webber said. "Seb did a reasonable long run, but we know what we need to do to improve the long run pace.

"We need to improve, the option tyre wasn't great for me, but we will work on it tonight."