Lewis Hamilton: Mercedes car is improving but 'not sure why' after stronger showing in practice at Miami Grand Prix

Lewis Hamilton and George Russell were encouraged yet mystified by Mercedes' return to contention at the Miami GP but have insisted the recovering world champions are not favourites despite topping Friday.

Having brought a raft of upgrades to the new American street race, Mercedes suddenly leapt from F1's third fastest team to frontrunners as Russell topped Charles Leclerc in Practice Two - with their 'porpoising' woes seemingly allayed and unlocking the pace they have been waiting for all season.

Hamilton was fourth, two-tenths off Russell, and said: "It feels similar to me. We seem to be quicker here, and later on they were explaining to us that we definitely have improved in some way - and I'm not exactly sure why that is.

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"We still have the bouncing, so we haven't cured it, but bit by bit we're improving the car."

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Mercedes put their upturn in fortunes down to a combination of their upgrades - including to their front and rear wings - and a Miami Gardens track that is lower downforce and so helps all teams with their bouncing cars.

"I don't really understand it to be honest, why we've hit the ground running," stated Russell.

"We always knew coming into the weekend that the conditions should suit us better, because we've been struggling with tyre warm-up. For sure that's played a big factor, but the car's working well."

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To further boost Mercedes' mood, Ferrari and Red Bull had difficult ends to Fridays with Carlos Sainz crashing and Max Verstappen suffering reliability woes.

But Russell added: "It's only Friday, we're not getting too carried away."

Hamilton behind Russell again, Red Bull wary of Merc

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Mercedes' form has led to paddock consensus that there may well be a genuine three-team fight this weekend in Miami, for the first time this season after Ferrari and Red Bull dominated the first four races.

Red Bull, Merc's rivals from last year and favourites for this weekend, were left impressed - with team boss Christian Horner telling Sky Sports F1: "I have been saying since pre-season it is only a matter of time before they sort themselves out.

"You can see that is starting to happen.

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"The characteristic of this circuit obviously helps as well but you can see they are starting to get on top of their issues and they are looking competitive."

While Mercedes were quick to warn against reading too much into the practice times, Friday did see Hamilton finish behind Russell - the team-mate he trails in the championship - in both practice sessions.

"I'm still struggling with the car," explained Hamilton. "George looked great out there - but we're trying a lot of different things. We'll converge and hopefully improve."

Russell added: "You have races where things work in your favour and others where everything works against you. Imola wasn't the strongest circuit for us but so far from what we see the car is working well around Miami.

"It's definitely been a really productive day for us and probably the most productive Friday we've had."

The litmus test for Mercedes comes in the shape of qualifying, live on Sky Sports F1 tonight at 9pm.

The full weekend schedule on Sky Sports F1

Saturday, May 7
2pm: W Series Qualifying
5.45pm: Miami GP Practice Three (session starts 6pm)
7.10pm: W Series Race One**
8.15pm: Miami GP Qualifying Build-up
9pm: Miami GP Qualifying*
10.45pm: Ted's Qualifying Notebook*

Sunday, May 8
3.20pm: W Series Race Two
7pm: Grand Prix Sunday: Miami GP Build-up
8.30pm: THE MIAMI GRAND PRIX*
10.30pm: Chequered Flag: Miami GP Reaction*
11.30pm: Ted's Notebook*

*Simulcast on Sky Sports Main Event (qualifying and race build-up simulcast from 8.30pm and 7.30pm respectively)
**Simulcast on Sky Showcase