Why Ferrari left Mercedes feeling flustered in week one of testing

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MONTMELO, Spain -- All the early signs from the first week of testing suggest Ferrari has stolen a march on its rivals. The Italian team, revitalised under its new team principal Mattia Binotto, not only looked quick on track, it was confident off it. After his first proper taste of the SF90 on Monday, Sebastian Vettel said the opening day of the test had been "unbelievable" and "close to perfection". By the final day, Vettel's new teammate Charles Leclerc was equally buoyant.

"The feeling in the car is good," he said. "Many laps, reliability is very good. We did all the programme we wanted every day, so this is extremely important for the team. For now, we are very happy."

The mood projected by the Mercedes drivers was less positive. After two sessions in the car, Lewis Hamilton said the upcoming season would be the team's "most challenging yet", adding that Ferrari look "very, very strong." Speaking on the final day of the test, teammate Valtteri Bottas said the feeling was that the world champions are already playing catch up.

"They [Ferrari] do seem very strong," he said. "No matter which kind of fuel load or engine modes they're running -- whatever you try to correct for -- they are quick. Short runs and long runs. I think we feel at this point they might be a bit ahead."

It's still not entirely clear how big that "bit" is, but based on what we have seen so far it is possible to get a feeling for it. In terms of outright lap times, the Renault was the fastest car with a 1:17.393, Mercedes was the third fastest team with a 1:17.857 and Ferrari was fourth with a 1:18.046. But there are several factors that skew the ultimate lap times in testing -- the biggest two being fuel loads and tyre compounds.

The softer the tyre compound, the more grip it offers and its not unusual for midfield teams to use the stickiest rubber to set the fastest times. Pirelli had five types of tyre at the test from the softest, stickiest compound, the C5, to the hardest, the C1. Unsurprisingly, it was the C5 that Nico Hulkenberg used to set Renault's headline time, when the team sent him out on a short run on Thursday afternoon to steal the top spot from rookie Alexander Albon, who had also used the C5s to set a quick time in the Toro Rosso. But it is possible to distinguish the glory laps from the truly fast times of the top teams by factoring in the performance difference between compounds.

Pirelli provides a rough guide of those performance differences based on the reams of data it collects. It's not an exact science as different cars use the tyres in different ways and a lot depends on the time of day, track conditions and fuel load, but at this stage of the year it is the closest guide we have and it helps unpick the raw numbers and formulate a more representative leader board.

Pirelli's estimates suggest there is a 0.6s gap in performance between the C5 and the C4 and a further 0.6s to the C3. Leclerc set Ferrari's fastest time, a 1:18.046, on the C3s, so if we minus 1.2s of lap time to put him on a set of C5s it ends up as a potential 1:16.846. Hamilton's 1:17.977 was set on C4s so that comes down 0.6s to a 1:17.377 on C5s -- marginally quicker than the outright fastest time set by Hulkenberg, but still nearly 0.5s off Leclerc.

But based on tyres alone, the times from Red Bull, Haas and Alfa Romeo also enter the mix, with all three teams setting impressive laps on the C3 compound on the final day. Applying the same arithmetic as above, Antonio Giovianzzi's fastest lap becomes a 1:17.311 for Alfa Romeo, Romain Grosjean's becomes a 1:17.363 for Haas and Pierre Gasly's a 1:17.580 for Red Bull.

But it's not always the fastest lap a driver sets that is the most impressive. Before setting their fastest times on Thursday, both Leclerc and Hamilton clocked times on the harder C2 compound that, 'tyre corrected', come out even faster. Leclerc set a 1:18.475 on the C2 and Hamilton a 1:18.800. According to Pirelli, there is an additional 0.7s gap between the C2 and the C3 to add to the 1.2s gap between C3 and C5, so that puts Leclerc at a potential 1:16.575 and Hamilton on a 1:16.900 once the maths is applied. Those numbers are further proof that the headline times are misleading, but they also tally with the other times to suggest Ferrari has an advantage over Mercedes of around 0.3s.

The big unknown with those numbers is the fuel load. The amount of fuel a car is carrying during testing is a closely guarded secret and it can be adjusted to either make a car look relatively quick or relatively slow while still allowing the driver to push. Ten kilograms of fuel will add as much as 0.3 to 0.4s of lap time, so a quarter of a 110kg tank can mask over a second of performance.

It's safe to assume that neither of the top two teams were running on vapours, and we know Leclerc's fastest time was set at the start of on a run of over ten laps, suggesting a fairly substantial fuel load, while Hamilton's was set on a five-lap run. A lap at the Circuit de Catalunya requires roughly 1.7kg of fuel, so Ferrari had, at the very least, over 17 kilos of fuel on board. By a very conservative estimate, he had at least 0.5s of pace locked away in fuel load alone. The short length of Hamilton's run means he may have been on less fuel, but there is nothing stopping teams sending a car out with more fuel than it needs to finish the allotted number of laps. So trying to second guess the fuel loads for Hamilton's lap time is more difficult. Leclerc, for one, believes Mercedes was running heavy to disguise its pace -- a practice known in F1 as "sandbagging".

"The performance has no sense for now, because it remains testing and they are probably not pushing, and we are not either," he said. "We don't know how much the others are sandbagging, so we'll see at the first race. Like I said, I think the most important thing for these tests is to do the programme of the day, and that is what we are doing, so we are happy."

Add to the above engine settings and how hard the driver was pushing, two factors that are even even harder to gain knowledge of, and we are back to very broad brush observations.

Nevertheless, the fact that Leclerc set two of the most imprssive times of the first week of testing on relatively long runs again hints at a fast Ferrari. Combined with the noises coming from the teams, it all points to the SF90 being the fastest car of the first week. From the opening day, the new Ferrari was setting competitive lap times -- Sebastian Vettel's best time on day one of the test was only a tenth off Leclerc's best effort on the final day using the same tyre compound -- and it ran without any major issues, clocking up 598 laps in total.

Mercedes completed 610 laps but appeared to be playing catch up in terms of performance. It was only on Thursday that the team turned its focus to setting faster lap times, but it did complete two race simulations on Wednesday -- something Ferrari did not attempt. In that respect, there should be a lot more to come from Mercedes in terms of raw pace but you bet Ferrari won't be standing still either.

"We don't think anyone is going with this kind of car in this test to the first race, including us," Bottas said. "We do have new parts coming before the first race, but we can't really rely on that, that it's going to be an upgrade. We do need to be even with this spec of car to try to get better and quicker."

And Red Bull also looks as though it is in the running. Like Mercedes, it shied away from performance running early in the week and it was not until a rear wing upgrade on Wednesday that it had a package that was properly suited to the Circuit de Catalunya. It's worth noting that Gasly's fastest time was set over an even longer run than Leclerc's, so when the fuel comes down and soft tyres go on, the Red Bull is also likely to feature near the front.

The second week of testing always offers a better read of the true situation. Race simulations, which require a full tank of fuel from the start, are a key indicator and performance runs start to resemble qualifying-style, low-fuel attempts. Those will help to confirm or deny some of the assumptions above and give an even clearer picture of where the top teams stand ahead of the first race in Melbourne. But after the first four days of the first test, Ferrari looks like the team to beat.