The stealth favourite for the Spanish GP

Mercedes set the pace on the opening day of Spanish Grand Prix free practice, while Red Bull caught the eye with its long runs. So for those fond of a superficiality not compatible with the complexities of grand prix racing, that might be an open-and-shut case in terms of how the weekend will go.

But behind those headlines lie the details that suggest things will be very different come qualifying and the race, because sometimes you have to look at the subtle hints and glimpses of the story that is playing out.

Those suggest things could be very different. The reality is that, after what was a difficult day's running, Ferrari is actually the stealth favourite at Barcelona.

Tipping Ferrari off the back of three consecutive pole positions might not seem especially bold, but this was a genuinely tough day for the team. Kimi Raikkonen lost around 20 laps thanks to a suspected engine problem in the afternoon, and both he and Sebastian Vettel (twice) made visits to the gravel trap.

But we did see enough to suggest things are better than they look. First, Ferrari's upgrades seem to be working well, even if the car hasn't been fine-tuned to get the best out of them at a heavily aero-dependent circuit.

As well as the very obvious halo-mounted rear-view mirrors (Vettel predictably confirmed they allow him to see what's behind him better) there are floor tweaks. Two different specifications of rear wing were also tried on Vettel's car, as well as the usual front-end aero detail changes.

"I think we can do better," said Vettel after the session. "Car balance wise we are not yet there but the good news is that everything we have brought here seems to work."

The key now is whether the pattern of Ferrari taking a stride from Friday to Saturday, in particular qualifying, holds true. Most likely it will, but Vettel sounded a note of caution that work must be done first.

Ferrari is within striking distance, even more so when you factor in it has more performance even than Mercedes to unleash in Saturday trim

"It doesn't come for free, we have to work for it," said Vettel after practice. "The car balance, I'm reasonably happy. I know there's a little bit more in the car and a little bit more in me if I get everything together. it should be OK tomorrow."

Team-mate Raikkonen was also quietly positive, in that understated way of his. He suggested there's no reason to expect the pattern of improvement for Saturday to change.

"It should not effect anything going forward," he said of the loss of track time he suffered. "I think it was pretty OK, it was a little bit messy with the wind and with the traffic but the laps that I did were pretty OK.

"It was a normal Friday, we tried things and tried to learn about everything and I don't see why it should be any different from the other races."

On the outright pace, the Ferrari was down in third, albeit only 0.326s off the pace. But there's a big caveat here, in that not only is Ferrari generally more subdued on Friday, but its fastest time was also set on the supersofts.

Usually, that would be standard procedure, and indeed everyone attempted qualifying simulations on that tyre. But many struggled to unlock its pace, with managing temperature particularly problematic - especially when it comes to the long loads on the left-front.

So, the times set by Mercedes and Red Bull were both on softs, and not on standard qualifying simulations. You could argue the more relevant comparison was the fastest supersoft lap, that of Max Verstappen, who was just 0.052s faster than Hamilton.

Single-lap pace

1 Mercedes 1m18.259s (Hamilton), soft
2 Red Bull 1m18.392s (Ricciardo), soft
3 Ferrari 1m18.585s (Vettel), supersoft
4 Haas 1m19.579s (Grosjean), supersoft
5 McLaren 1m19.722s (Vandoorne), supersoft
6 Force India 1m19.962s (Perez), soft
7 Renault 1m20.183s (Hulkenberg), supersoft
8 Toro Rosso 1m20.373s (Gasly), soft
9 Sauber 1m20.501s (Ericsson), supersoft
10 Williams 1m21.556s (Stroll), medium

So, that means Ferrari is within striking distance, even more so when you factor in that it has more performance even than the Mercedes-powered cars to unleash in Saturday afternoon trim. In line with what we've seen in the races, things then even up across the three engine suppliers fighting it out at the front.

"What I'm told is it has swung a little bit the other way," said Lewis Hamilton when asked about the erstwhile Mercedes qualifying advantage. "So qualifying they [Ferrari] are a little bit up on us, and then in the race I think pretty much the same."

When it comes to long-run pace, the picture is also skewed by the unpopularity of the super-softs. Based on what we saw on Friday, the soft will be the tyre of choice for the race.

As Pirelli estimates the peak performance gap between supersofts and softs at 0.4s, expect the big guns to try to get through Q2 using the softs to then start on it. The medium also looks like a strong race tyre, as Valtteri Bottas's long run confirms.

Whatever happens, the soft still gives the best indication of relative race pace. Indeed, even though the supersoft is not suffering from thremal degradation problems, based on today the soft will be preferred. Hamilton's bafflement at his pace while on his supersoft run is testament to that.

What we can't be sure of is the overall impact of Ferrari's messy day. There is potentially a knowledge deficit about what might be the key tyre

Pirelli couldn't offer a clear explanation for the fact the supersoft seems so unappealing to drivers and teams, although Mario Isola suggested perhaps it was down to the tread moving around slightly.

"It will be very interesting to understand why we have this situation," said Isola. "The supersoft is giving a very small delta and it seems that drivers are preferring the soft.

"One possible explanation, and this is just experience I need to check the data, is that maybe the supersoft is a bit like jelly, moving a little bit. This is a feeling that drivers don't like, they like a feeling that is more solid and more precise.

"We are talking about a small movement, the tread is not moving a lot, but they are Formula 1 drivers so they feel everything."

It's true that the Red Bulls looked very strong on this tyre, reeling off lap after lap at a strong pace without dropping off - and clearly ahead of Mercedes. But with Raikkonen out of the picture after 16 laps, Vettel did very little running on the softs.

The below averages are based on six-lap runs, but in Vettel's case he's on top with just three laps. Now that can only be considered a hint of pace, rather than definitive proof, but it supports the idea Ferrari is stronger than it looks at first glance.

Long-run pace

1 Ferrari (Vettel) 1m21.342s*
2 Red Bull (Verstappen) 1m21.458s
3 Mercedes (Hamilton) 1m21.747s
4 Haas (Magnussen) 1m22.692s
5 McLaren (Vandoorne) 1m23.477s
6 Force India (Ocon) 1m23.403s
7 Renault (Sainz) 1m23.608s

*three-lap run

As well as the asterisk against Ferrari, it should be noted that Williams and Toro Rosso did not complete long runs on softs. Sauber, meanwhile, did with Marcus Ericsson but it was on ageing rubber that would place the Sauber almost two seconds off Renault - unlikely to be a fair reflection of its race performance.

What we can't be sure of is the overall impact of Ferrari's messy day. Raikkonen might have downplayed his loss of laps, but it prevented him from completing his long-run using what is more often than not the 'opposite' tyre to Vettel. As Vettel did his serious long-run work using the supersoft, that means there is potentially a knowledge deficit about what might be the key tyre.

But Ferrari has got a good handle on this car after its difficulties during pre-season testing and during the first weekend in Australia, when it had to bring back its 2017 front wing as a test part to understand something that was not working as hoped.

It doesn't have the same extent of troubles in keeping the tyres in the operating window as Mercedes has, and doesn't have the qualifying disadvantage that holds back Red Bull. That's what means it remains the most likely to have the advantage going into the race of track position thanks to its Saturday strength.

And remember, this is a circuit where the driver who starts on pole tends to win - 14 times out of 18 in the 2000s - so if Ferrari can have the one-lap edge, it has control on Sunday.

Lewis Hamilton used the word "sandbagging" to describe Ferrari's performance, but that implies a deliberate attempt to hide pace

And things do tend to get better after Friday for the reds. Lewis Hamilton used the word "sandbagging" to describe Ferrari's performance, but that implies a deliberate attempt to hide pace. What Ferrari was actually doing is focusing on its usual programme and, even though things didn't go that well, revealing some subtle signposts pointing to what might be possible.

It still looks close up top, but the smart money remains on Ferrari for qualifying. After that, we could be on for another very close race with all three teams in the hunt. And given Barcelona is a track where aerodynamics are even more important than at the vast majority of F1 circuits, that will bode very well for the rest of the 2018 season for Ferrari.