Daniel Ricciardo insists Red Bull can beat Mercedes in 2017, despite the rival teams' contrasting first two days of winter testing.

Triple world champions Mercedes have once again started pre-season in ominous fashion, completing lengthy stints and setting fast times in their W08 as the sport enters its new era in Barcelona.

Day Two: Ferrari faster than Mercedes

Red Bull, on the other hand, were blighted by Renault engine concerns on Monday, while Ricciardo and Max Verstappen were both a couple of seconds adrift of the fastest Silver Arrow on their respective day's running.

Still, Ricciardo remains confident of a turnaround once the campaign begins, with Red Bull expected to reveal their full pace potential once aerodynamic improvements are added to the RB13 for Test Two next week.

"We can beat them," the Australian told Sky Sports News HQ. "We've got the same set of rules as everybody else so there's no reason why we can't across the course of the season."

To sum up their seemingly bullet-proof new challenger, Mercedes have racked up a combined 319 laps so far, 83 more than any other team.

Stroll won't be put in a spin

"Mercedes can, as they have the past few seasons in winter testing, come out strong and reliable, which I think we all expected," Ricciardo added.

"The rules are different, but they're not so different that Mercedes were going to drop from first to fifth. We expected them to be quick - we're still not sure how quick we are or how quick Ferrari are."

Watch as the new Red Bull takes to the track in Barcelona on day one of the first test. Watch as the new Red Bull takes to the track in Barcelona on day one of the first test.

Ferrari, of course, can also not be discounted from the title battle. The SF70-H appears to be just as reliable as the Mercedes, while Kimi Raikkonen topped the timesheets on Day Two on the soft tyre.

Day Two: Ferrari ahead of Mercedes

Verstappen was third fastest behind Raikkonen and Mercedes' Lewis Hamilton on a first day in the RB13 he described as "very positive".

Asked by SSN HQ if Mercedes' strong showings were nonetheless a worry, Verstappen replied: "I'm sure they will always be quick, but for us at the moment it's all about getting the mileage in and seeing if there are some issues.

"For us it was a very positive day and we'll focus later about that [lap times]."

Where Red Bull hope to make their superiority count is through aerodynamics, which was thought to be the key to success in 2017, led by technical chief Adrian Newey.

But even Newey, winner of 10 world championships during his time with Williams, McLaren and Red Bull, was wary of the gap his team must make up if they were to claim a first title since 2013.

"Undoubtedly, it's still an engine formula," Newey told Sky F1's Ted Kravitz.

"We're still in a position where one per cent power is worth one tenth of a second, and one per cent aero is also around a tenth of a second. So if you're getting five per cent more out of the engine, you need to find five per cent from aero for the same lap time.

"We're still trying, but we don't know. We know what we've achieved over the winter but we have no idea if that's better or worse than our rivals."