Mercedes F1 team forced into problems by Ferrari threat

The world champion team was very reliable in pre-season testing but has encountered a series of problems during race weekends, particularly on Lewis Hamilton's car.

In Russian Grand Prix qualifying, Hamilton suffered an identical power unit problem to the one he suffered in China and required parts to be flown in overnight.

In the race, his chase of team-mate Nico Rosberg ended when he encountered a water pressure problem while Rosberg had to back off because of an issue on the MGU-K.

Speaking in a video on the Mercedes YouTube channel, team boss Wolff said: "With the regulations staying stable, you want to extract every single bit of benefit out of the engine and therefore it becomes more difficult.

"Ferrari has made a huge step over the winter and this is why we are pushing boundaries and sometimes when you reach the limits, you just need to find out. And this is where we are."

Wolff said the causes of the two problems were not yet evident but working groups have been set up to get to the bottom of them.

"Because we are pushing so hard, we had an issue on Nico's car where on the MGU-K, we saw some overtorque, which is quite a worrying signal because it might break," he said.

"With the current regulations, you are not really allowed to tell the driver so it was quite difficult to manage that.

"On Lewis's car, we had a cracked carbon pipe which looks like it being a problem on the quality of the pipe itself. We need to look at it.

"We are trying to analyse and find the root causes for the problems and it's not evident. It's a complex issue.

"There are a couple of project groups looking at each of the possible problems and I'm sure we will overcome these and come out on top of understanding the issues."

LETTER WAS A THANK YOU TO FANS

Mercedes wrote an open letter to its fans on Wednesday, responding to suggestions on social media that Rosberg is favoured over Hamilton.

"This was a letter to our real fans," Wolff said.

"What you could see on social media is that they support us, they suffer with us.

"They argue for our cause and that was so nice, so we felt we wanted to give an insight as to what was happening and how we felt and thank them for their support.

"We want to be transparent in our communication. There is nothing we are hiding.

"This is why the letter was a good example and a good way of sharing our feelings and thanking for support of our fans."