Problems for the front wings of both Red Bull cars was the outstanding feature of Red Bull's disappointing Spanish Grand Prix on Sunday in Barcelona.

"It was a difficult race and a hard day in the office," said Sebastian Vettel. "I'm not entirely happy."

The front wing problems for Vettel and his team mate Mark Webber appear unrelated and coincidental at this stage, rather than a sign of underlying problems.

"I don't know what the problem was when we had to change the nose of the car," said Vettel. "I wasn't sure if I had damage or something stuck at the front - maybe a piece of rubber or something. I tried another lap, but it wasn't the right thing to do, so we decided to come in and change the nose to make sure."

"I don't know where I got damage to my front wing, but I had to pit for a new nose, said Webber of his own unscheduled pit stop. "I lost a lot of time with that - and on the few laps before when it started playing up."

Beyond that, Vettel's race at the Circuit de Catalunya was hit by a drive-thru penalty midway through for ignoring yellow flags, while Webber was simply off the pace.

"Unfortunately Sebastian had a drive-through penalty for an incident under a yellow flag, which I believe is because he had the DRS open," said team principal Christian Horner. "For Mark it was a tough race with the wing change early on and then unfortunately a mystifying lack of pace, which resulted in him spending a lot of the race looking at the back of Nico Hulkenberg's car."

"It was a mystery with the pace," agreed Webber. "I was stuck behind Force India, you see the McLarens weren't doing so much and Seb was just chipping away."

"We were definitely stronger towards the end of the race and it was good fun, but when it's up and down and up and down, it's quite difficult," added Vettel. "We could have finished maybe one position higher up, but we had a good recovery in the end."