Lewis Hamilton has admitted Mercedes are "missing something" after revealing he was "battling the same issues" throughout Friday at the British Grand Prix.
Hamilton was 12th and 15th in the two practice sessions at Silverstone - over one second off the pace compared to pace-setter Max Verstappen.
Mercedes had a difficult Austrian Grand Prix last week but were hoping the high-speed nature of Silverstone would see them back on form, having had podiums in Spain and Canada.
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"Car-wise, we are battling the same thing the majority of the time. It's a tough car to drive. No matter what we do to set it up, it continues to be a tough car to drive," said Hamilton.
"On a single lap I didn't feel any improvement between tyres, which shows something is wrong. We are missing something. The long run didn't seem to be too bad, so that's a positive at least."
Carlos Sainz was told about Hamilton's long run pace on the softs and the Ferrari driver responded "that is quick" towards the end of Practice Two. However, the seven-time world champion did not have the same optimism.
"It didn't feel particularly great, but it most have felt worse for others because they potentially weren't as quick, or had more degradation," he said.
"The last part of my run was starting to be more consistent for whatever reason. It could be wind or balance or me getting used to the balance. This track is all about trying to weight these scales the whole way around and making compromises here and there.
"There's such a fine edge on the balance and such a big balance window. It's back and forth. It's like one end to the other end of the spectrum from braking to turning to mid to exit of every corner, so it's a good battle."
Russell: We were nowhere
It was no better for George Russell as he was 14th and 12th in the two sessions on Friday at Silverstone.
"Definitely not our finest Friday. I think conditions will be different [on Saturday] but we need to try and get to the bottom of it," said Russell.
"The pace in Practice One was looking reasonably good on the medium tyre and we thought it was right up there if we took the softs but in Practice Two we were nowhere, so we need to understand it."
Hamilton added: "Me and George were just talking. I'm over here with the setup and he's over here. He's like, 'I'm thinking to coming where you are but then your lap time is slow' and I'm saying 'I'm thinking of coming to where you are'.
"The balance...we will try and work on it tonight. Mick will do some work in the sim, so we will come up with something [on Saturday]."
Albon: Williams pace unexpected | Normal day for us
While it was a disappointing day for the trio of British drivers, as Lando Norris also struggled for McLaren, London-born Alex Albon led an excellent day for Williams.
Albon was third in the opening practice session and backed it up by claiming third again in Practice Two.
"It was a bit surprising in some ways, unexpected. We were not playing around doing weird things, it was a normal day for us," said the Williams driver.
"And we crossed the line and we are in the top three, so a bit of head scratching but at the same time the car feels good. We have an upgrade on the car that we have had for two races now.
"On the simulator it has shown to be a bit more effective on the high speed than the low speed and we have not really had too many high speed tracks recently. So it's the first time we have seen the package on a quick circuit and it's looking good.
"But we have to keep ourselves grounded It's chipping away. The wind the way that it is, it's so strong. It doesn't feel good. It feels terrible for everyone, but clearly less terrible for us."
Norris 'a bit confused' about McLaren pace
Norris had a similar day to the Mercedes pair, ending Practice Two in 14th, and is hoping the expected rain on Saturday comes during Qualifying.
"It was a difficult day. It's never easy here - difficult with the wind, bumpy circuit, trying to get downforce levels correct," said the McLaren driver.
"So not the most straightforward. We made some small steps but not the most confident in the car today. On the hard tyre in P2 I felt more confident than I was on the soft. Not quicker, but we put the softs on and didn't go that much quicker. So a bit confusing.
"I just didn't manage to transfer much of the lap time onto the soft tyre. We seemed better in P1 and not so good in P2. It did get more windy so maybe that played a little bit of a part."
Sky Sports F1's live British GP schedule (all F1 sessions on Sky Showcase)
Saturday July 8
9:15am: F3 Sprint
11:15am: British GP Practice Three (session starts 11:30am)
1:10pm: F2 Sprint
2:15pm: British GP Qualifying build-up
3pm: BRITISH GP QUALIFYING
5pm: Ted's Qualifying Notebook
Sunday July 9
8:10am: F3 Feature Race
9:50am: F2 Feature Race
11:50am: Porsche Supercup
1:30pm: Grand Prix Sunday - British GP build-up
3pm: The BRITISH GRAND PRIX
5pm: Chequered Flag: British GP reaction
6pm: Ted's Notebook