Mercedes chief strategist James Vowles and trackside engineering director Andrew Shovlin admit that there are "no immediate answers" to the W12's rear-end instability.

"Snappy and unforgiving," is how Valtteri Bottas summed up the W12 at the end of pre-season testing, and while rivals ponder how much more Mercedes might have up its sleeve, there is no doubting that the Finn and his seven-time world champion teammate, Lewis Hamilton clearly found their 2021 car a handful.

Speaking in the German team's video debrief, chief strategist James Vowles and trackside engineering director Andrew Shovlin admit that there are "no immediate answers" to the car's rear end instability.

"It was pretty evident that the car was handling poorly," says Vowles, "and conversely the Red Bull in fact was a very stable car especially through the last sector of the lap.

"I think that's a fair observation," he continued. "It was visible to the outside and I would say the lap times mirrored that as well.

"But it's also fair to say that we don't have answers as we are sat here now," he admitted, "it is just 24 hours after the end of the test. Huge amounts of data available to us and now a long journey ahead to try and understand what was causing that."

Shovlin admits that the team, like its rivals, was affected the winds that battered the Bahrain circuit throughout the three days of testing, but that the rear end of the W12 appears to have been particularly susceptible.

The wind made it tricky," says Shovlin. "When the wind is behind the car, you lose a lot of downforce because effectively the air speed is reduced, so some corners where the wind was behind, it was prone to doing that. Then also the tyres are quite easy to overheat on that circuit and if you start sliding, you tend to lose grip and it gets worse. So, there are a few problems.

"Importantly, we could see that some of our competitors weren't struggling in the same way as us, so we need to put quite a focus on understanding why the rear end was a bit weak, how we can get it more stable and predictable and that work is going on now.

"Hopefully when we get to the race weekend it won't be so difficult for the drivers because they were having to work pretty hard to do the lap times that they were doing."

Looking ahead to the season opener, Vowles admits that Red Bull heads to Bahrain in better shape.

"I would say Red Bull are ahead on performance, they are the class act from the test," he says. "But it is a test, it is not a race, and it is one event out of 23.

"Are we going to have a close season? I would say so. Red Bull are a fierce adversary, they've got a strong package and clearly came out of the box very, very quick."