Ferrari can't explain lack of F1 pace at US Grand Prix - Vettel

Vettel and team-mate Kimi Raikkonen were best of the rest in Japanese GP qualifying behind the Mercedes drivers and recovered to fourth and fifth after each taking five-place grid penalties.

It led both drivers to say they believed Ferrari was back ahead of Red Bull but at Austin the team ended up behind Mercedes and Red Bull, with Raikkonen fifth and Vettel sixth.

"I'm not happy with the competitiveness we've shown today," said Vettel.

"The circuit is similar in many regards to two weeks ago in Japan but we seem to struggle more for overall pace here than two weeks ago."

When asked if he could specify what was different compared to Suzuka, Vettel said: "I can't give you an answer, we don't exactly know.

"On Friday, we saw we weren't yet on the pace.

"We improved for today, the feeling in the car wasn't that bad and throughout qualifying, both of us were reasonably happy with the balance.

"We're just not quick enough.

"A lot of work is going in trying to understand what happened but for now, we have to take it that way and fight as much as we can in Sunday's race."

Vettel admitted he didn't get the best out of his laps either.

"Both Q3 laps, I wasn't happy," he said. "I probably pushed a little bit too hard.

"We know it backfires on these tyres but that's not an excuse, I should have done a better job.

"It's part of the reason why I'm not entirely happy with today, the gap to the cars in front is what I don't like.

"We had a good run the last couple of races, coming here and seeing we're not as competitive as we thought is not good news."

Raikkonen was equally unhappy with Ferrari's performance at Austin.

"It's a disappointment where we finished today but handling wise, there was not a lot to complain about," he said.

"It's just pure lap time we are missing, we have to go faster.

"It's not very easy to fix otherwise we would have fixed it already.

"But we've seen that before this year a lot, that it changes from circuit to circuit."