The World Champions ran both versions of the RB8 chassis that has been seen so far this season: the launch model and the newer version introduced during the final pre-season test in Barcelona which features a different exhaust design.

Vettel in particular has struggled with the balance of his car since the new exhaust was introduced. Much like the pacesetting McLaren, it blows more towards the rear wheels in much the same way - albeit with a reduced effect - as blown diffusers.

Red Bull pioneered the development of the concept, although its ability to generate downforce was reined in significantly at the end of last season.

Although light rain hampered running during the opening practice session, Vettel and Webber ended the day respectively third and fourth quickest behind McLaren's Lewis Hamilton and Mercedes' Michael Schumacher.

"I think I felt a bit more comfortable today, a bit more together so we'll see. It's a bit tricky now to say if we're going to be competitive. It's fairly close but I think McLaren is still very quick in all conditions and on all fuel levels," the double World Champion said.

Best package

With Red Bull also trying a new specification rear wing on Friday, Vettel admitted he remains unsure exactly what specification of car he will take into the weekend.

"I don't know yet, we'll see," he added. "For now I think we're pretty happy with the set-up of the car, a bit more together, so now we need to look at the data. It's not the only thing we tried obviously but it's the biggest thing that we tried today but we had a look at some other stuff as well.

"Mark did as well, so now we can compare the two across cars and see what's the best package we can come up with."

Webber added: "I'm pretty happy today. We got through a lot of information. We were quite worried about the weather today so in general it's a good opportunity to check a lot of things on a Friday like this because we have two tight grands prix again - here and Bahrain - so it gives us a little bit of direction and focus having done the comparisons of the car.

"I obviously haven't been in this car for a while - I said that today - and neither has he; it's the first time in a while he's been back in it. There are changes in the concept of how the cars work on different parts of the lap.

"So if it goes right tonight then we might rob a little of each other's strengths and weaknesses."