Andrew Benson
BBC Sport’s chief F1 writer

The introduction of the halo head protection system was inevitably one of the talking points of the start of testing, with most drivers saying much the same thing - they didn’t particularly like the aesthetics, but it didn’t affect visibility, and it was just a bit harder to get in and out.

Renault’s Carlos Sainz did, though, come up with a new observation after driving in the rain in the afternoon. “When it started raining a bit, you could not see the rain on the visor. The halo was not allowing the rain drops to go in the visor so you could not really see if it was raining a lot, (just) feeling it in your hands.

"This kind of rain that sometimes to us drivers really bother us as you don’t know if you can push 100% or not, you just had to guess it and see how much rain it was, as our visor was completely dry and outside it was raining - a bit tricky there.”

Image source, Getty Images

And Carlos Sainz is storming this session as well.

OK, he is the only one to set a timed lap, but there he is proudly at the top of the times. What a day for Renault. Dominant.

Image source, Getty Images

Andrew Benson
BBC Sport’s chief F1 writer

Renault had a particularly impressive day to start pre-season testing. Nico Hulkenberg was up at the sharp end of the times all day and ended it fourth, just 0.368secs off the pace, and 1.6secs quicker than the next fastest car.

And there was no hiding how pleased the team were, even if their public pronouncements were necessarily cautious. Carlos Sainz was less fortunate in the afternoon, the dropping temperatures causing him problems getting his tyres up to temperature.

But he still ended up fifth fastest. “A solid start,” technical director Nick Chester called it. It looked rather better than that.

Image source, Getty Images

Alex Holland-Martin: Has anyone got a F1 car I could borrow and give the #bbcf1, external team to report about.

Alex has stepped up to the plate. A selfless act. Anyone got a car spare? I'm hoping you're already at the circuit or at least close by.

Peter Chymera: I'm interested in the Toro Rosso Honda vs McLaren Renault battle. Shall we take the Alonso chicane manoeuvre yesterday as a sign that despite perceived improved reliability, the Honda power is still significantly down on rivals? Would love it if Honda catch up this season.

Kieran Reynolds‏: Testing always shows promise. McLaren will be good mod team at best. Expect last year's order although bit more closely packed.

Phil Evans: What I want to see today: Someone paint the Sauber or Williams so we can tell them apart? Aside - I see the McLaren has fitted some big nets behind the front wheels to catch them if they come off, but wasn't it the rear that failed? ;)

Sauber...

Image source, Getty Images

Williams...

Image source, Getty Images

Great scenes. Carlos Sainz sets a time. His effort of 1 minute 34.177 seconds comes on the intermediate tyres.

It is almost 14 seconds off the best time set yesterday, Daniel Ricciardo's 1:20.179.

Andrew Benson
BBC Sport’s chief F1 writer

Ferrari had a low-key but impressive start to their campaign, Kimi Raikkonen starting day one a little later than some of the others but quickly up to speed when he did. “It was OK,” he said.

“Obviously the weather is far from ideal, it’s very cold, so it has nothing to do with how we usually run the tyres or anything.

"We did the amount of running that we could, in these conditions, and everything felt, I would say normal. It’s early days but so far it’s OK.”

Image source, Getty Images

Dan Knutson
F1 journalist in Barcelona

The cold temperatures and rain yesterday, the dusting of snow overnight, and the freezing weather today has sparked the same old debate about if it would be better to test in Bahrain. On the plus side, it is a lot hotter in Bahrain. On the negative side, the logistics and costs for the teams to go to Bahrain are much tougher than Barcelona where personnel and car parts can go from factory to paddock in just a few hours.

"The reality is that we are never going to drive in these conditions,” Daniel Ricciardo said after setting the fastest lap time yesterday. “Part of me wishes we were somewhere else like Bahrain where you can get some real testing in real temperatures. I don’t want to be negative but it is a bit frustrating when you can’t do too much.”

Last night, when the sleet was coming down, some of us reporters stood outside hearing what Haas team principal Guenther Steiner had to say about the situation.

“This is not a normal cold (for Barcelona),” he noted, “there is a whole cold front going through Europe. Look at the UK. At the moment I’d love to be in Bahrain at 30C and standing in the sun. But then again, once you are missing a part, you say: Why am I here! Next week will be better here.

“You can do a little bit more than systems checks. You can check some aero data. Whenever you go out with these cars you learn something. But is it efficient testing? By no means.”

Image source, Getty Images

Why aren't you reporting on all those timed laps?

Er, well, there haven't been any. As Haas kindly reminds you with this GIF.

(BBC Sport app users may need to click on the link to see the gif).

So, what's happening at Mercedes? Well, they are watching too much Frozen for sure.

It will be interesting to see what New Zealander Hartley can do this year. He only took part in the last four races of the season, but is highly-rated by Toro Rosso, who gave him this season's drive as he replaces the dumped Daniil Kvyat.

From his four races at the tail end of the 2017 campaign, he had a 13th-place finish in the USA and 15th in the last race at Abu Dhabi, but also failed to finish in Mexico and Brazil.

For Kvyat, what a miserable two years. He has gone from being at Red Bull, then demoted to their sister side Toro Rosso, then binned off altogether by them and is now only in a development role for Ferrari.

Image source, Getty Images

Andrew Benson
BBC Sport’s chief F1 writer

While McLaren were in the wars yesterday, it escaped no-one’s attention that their former partners Honda had an apparently trouble-free day.

Brendon Hartley completed nearly 100 laps - only Red Bull and the factory Renault team doing more - and ending up just 0.017secs off Fernando Alonso.

“It was a really positive day. We had no issues at all. We stopped early because of the weather, almost icy conditions out there. But everything felt pretty good straight out of the box, obviously we had a lot of test items that we didn’t get to complete because of the weather but I think getting through 93 laps was a great start to the campaign with the new Honda Toro Rosso.

"Balance-wise we were pretty comfortable straight away but I still think there’s a lot of potential to unlock, which will be the same for all the teams. I don’t know what I should say but actually the drivability is the best I’ve driven in the last two years in a Formula 1 car. It was really, really positive all things directed towards Honda so that was really good. No complaints so far and we had a perfect day in terms of reliability.

Image source, Getty Images

Adam Lyon: What I want to see on day two? - Red Bull to keep up yesterday's pace - Leclerc to put on a good showing - Renault to show the consistent quick times that they did yesterday - Vandoorne challenging up the top - Some twitter banter from the teams to keep us occupied.

Ross Wilson: Itching to see McLaren heading back up the grid to where they belong. The fear is that times have changed and moved on, both for a privateer team entry, and a hugely talented F1 driver. Are their best times behind them both?

Jordan Harrop: Already got a feeling the pack’s gonna be closer this year, should make for great racing! Can’t wait for lights out in Melbourne...

Sunday, 25 March. Not long now.

Image source, Getty Images

Right, so what's going on at the moment...

Ocon's on the track in his pink Force India...

...as is Stoffel Vandoorne in his orange McLaren...

...and don't forget Carlos Sainz in his black and yellow Renault.

After Daniel Ricciardo topped the times yesterday, Red Bull team boss Christian Horner said: "It certainly was a positive first morning.

"It is always difficult to read too much into these things, but over 60 laps and sensible lap times was a good start to the pre-season testing.

"And it was exactly what we have been aiming to do over the winter to get ourselves onto the front foot coming into the testing.

"So the whole team has worked incredibly hard to get into the position where we are.

"But, of course, it is just the start of a very long journey, and it is all about how we develop RB14 from this point all the way through to Abu Dhabi."

Image source, Getty Images

Red Bull last season saw Daniel Ricciardo fail to finish in six races, with seven retirements from Max Verstappen.

However, both men got themselves on to the top step of the podium at least once last season and it would be brilliant if we had a genuine three-way title fight between Mercedes, Ferrari and Red Bull this time around.

Very, very, very early signs are good.

Andrew Benson
BBC Sport’s chief F1 writer

Daniel Ricciardo had the best first day of testing for Red Bull perhaps of the whole hybrid era, with more than 100 laps completed and fastest lap of all, by 0.17secs from Mercedes Valtteri Bottas.

The Australian was reasonably optimistic afterwards, despite the difficult weather conditions. “You feel if you have got a bad car or a pretty good car. It wasn’t bad, so that is good,” Ricciardo said. "I was not crying so it was a positive day. The performance - it was nice to see yourself at the top of the times, but it is always hard to get a gauge on that, especially day one. Reliability – I don’t think we’ve ever done 100 laps on day one.

"Not since I’ve been with the team. That is positive. We did long runs as well. One run was 35 laps or something. So that is positive. And the pace does not seem to be too bad, so a good day. But with the temperatures you can only learn so much.”

Image source, Getty Images

These are the times that today's drivers will be hoping to beat. Of this list, only Bottas, Hulkenberg, Sainz, Hamilton and Sirotkin are going again today.

Fastest times from day one

1. Daniel Ricciardo (Aus) Red Bull-Renault - One minute 20.179 seconds
2. Valtteri Bottas (Fin) Mercedes - 1:20.349
3. Kimi Raikkonen (Fin) Ferrari - 1:20.506*
4. Nico Hulkenberg (Ger) Renault - 1:20.547
5. Carlos Sainz (Spa) Renault - 1:22.168*
6. Lewis Hamilton (GB) Mercedes - 1:22.327
7. Fernando Alonso (Spa) McLaren-Renault - 1:22.354**
8. Brendon Hartley (NZ) Toro Rosso-Honda - 1:22.371*
9. Lance Stroll (Can) Williams-Mercedes - 1:22.452*
10. Romain Grosjean (Fra) Haas-Ferrari - 1:22.578*
11. Marcus Ericsson (Swe) Sauber-Ferrari - 1:23.408*
12. Nikita Mazepin (Rus) Force India-Mercedes - 1:25.628
13. Sergey Sirotkin (Rus) Williams-Mercedes - 1:44.418*

* = time set on soft tyre; ** = time set on super-soft tyre; all other times on medium

Image source, Getty Images

Messiamz: Alonso for top three this season! I’m so sure I’m putting money on it. He is the best driver on the grid in my eyes.

Toby Godfrey: Is @Max33Verstappen, external running today? As @danielricciardo, external obviously ran yesterday, and very well looking at the times.

Steve White‏: Cards on the table I'm a big Hamilton fan. But one hope this year is to see Max competing every race. He is soooooo exciting.

Messiamz - brave, very brave. Toby - Indeed he is. Always good to see Verstappen in action, but sadly no Ricciardo today. Well, he's not scheduled to be out anyway.

We are talking about hopes and expectations.

My main hope is that, at some point in this season, we get to see Robert Kubica racing in a grand prix.

He missed out on a main Williams seat this season, losing out to 22-year-old Russian Sergey Sirotkin, but is still a Williams reserve driver and gets another chance to show what he can do this afternoon.

What a story it would be if Kubica raced in another Formula 1 race. The Pole has not raced in F1 for seven years after suffering life-changing injuries in 2011 in a rally accident, but he is still hopeful, as you can see in this interview with the BBC from December.

And these are the guys that we are paying attention to today.

• Mercedes - Valtteri Bottas and Lewis Hamilton
• Ferrari - Sebastian Vettel
• Red Bull - Max Verstappen
• Force India - Esteban Ocon
• Williams - Sergey Sirotkin and Robert Kubica
• Renault - Carlos Sainz and Nico Hulkenberg
• Toro Rosso - Pierre Gasly
• Haas - Kevin Magnussen
• McLaren - Stoffel Vandoorne
• Sauber - Charles Leclerc

BBC Sport app users may need to click on the link to see the tweet.