This weekend's Spanish Grand Prix marks the start of Formula One's European season and will see a return to the venue of pre-season testing at the Circuit de Catalunya outside Barcelona. The proximity to the teams' bases around Europe means it is targeted as a race to bring the first big car update of the season, with underperforming teams looking to right the wrongs of the first flyaway races while those making strong starts aim to extend their advantage. Ahead of the flight to Barcelona, we take a look at the five teams needing to make a step forward this weekend.
Ferrari
What's the problem?
Four straight defeats to Mercedes has left Ferrari 74 points adrift in the constructors' championship while Sebastian Vettel is 35 shy in the drivers' standings. Even with 17 races remaining, those numbers are big, especially as Mercedes has shown few weaknesses and, so far, Ferrari has looked less reliable. It's not game over by any means, but the Italian team desperately needs a win.
What to expect
An upgraded power unit four weeks earlier than expected! It will be combined with upgraded oil from supplier Shell and, for Ferrari to make such a big change in its planning, must be putting out very promising numbers on the dyno. More aerodynamic upgrades will follow to add to the new turning vanes, barge boards and floor the team brought to Baku.
What they say
Mattia Binotto, team principal: "It's time for the Spanish GP, traditionally a race where most of the teams bring some updates, therefore we can expect to see a step up in performance from our competitors. We are currently behind in the championship and we have to catch up, which we know means that our development work will be the key to this season. Having brought a new aerodynamic package to Baku, we will also bring some developments in this area to Barcelona.
"On top of that, we will have a new power unit that we are introducing ahead of schedule, as the second specification was due to be brought to Canada. Shell, in close collaboration with our team, has developed a different formulation of race lubricant that will also be introduced with the new power unit, delivering increased performance. It's only down to a big team effort with everyone pushing hard to make up ground that we have been able to bring these developments forward."
What we say
The most frustrating thing about Ferrari's first four races of 2019 is that the car is clearly better than the results suggest. Mistakes -- from both the drivers and team -- have proved hugely costly and in terms of pure pace victories were possible in Bahrain and Baku.
The season is only four races old, but it's not an exaggeration to say Spain is a must-win for Ferrari. This was the location where the SF90 looked every bit a world-beater in pre-season testing and if it can't edge ahead of Mercedes this weekend, the hope of it doing so consistently over the rest of season takes a big hit. The team is clearly pushing hard -- it managed to bring a sizable upgrade package to Baku -- but Mercedes is not standing still and is planning upgrades of its own for Spain.
Red Bull
What's the problem?
Another winter, another start to the season off the pace of Mercedes and Ferrari. There were big changes at Red Bull as it switched to Honda power during the off-season and perhaps this was always going to be a development year. But it's still disappointing to see a team like Red Bull, and a driver like Max Verstappen, off the pace.
What to expect
Unlike previous years, Red Bull says its Spanish GP update package is relatively small. Whether we should believe that or not, we will find out in Barcelona. Keep an eye out for a new motorhome in the paddock though...
What they say
Christian Horner, team principal: "I think we have closed the gap [to Mercedes and Ferrari] since the beginning of the year. In Melbourne we had a strong race, I think Max [Verstappen] was pushing Lewis [Hamilton] for the majority of that Grand Prix, Bahrain was a tough race for us but I think actually exposed some things that we've managed to improve since then. Then China has been a stronger race, and then again in Baku, even more so.
"There are a few circuits coming up that hopefully should suit us. We're at race four, Max is 36 points behind and it's a long, long way to go in the championship. We just have to take it one race at a time, but three fourth-place positions in a row is getting a little bit boring now -- we want to be fighting for the podium again.
"Our upgrades for Spain are fairly subtle. It's basically evolutions so it'll be the usual. Front and rear wings upgrades. But it's evolution rather than revolution."
What we say
The main concern for Red Bull ahead of the year was how Honda would perform, but the Japanese manufacturer has made a solid start. If anything, the concern switched to the chassis side at the opening few races and it was only in Baku that the team really started to extract something closer to true performance. But Baku was still a power track, so seeing the Red Bull on a circuit like Barcelona, which rewards a strong aero package, should provide a better indication of how it will perform over the rest of the season.
The small upgrades Horner refers to suggests the team is keeping its powder dry and is perhaps happier with its development direction than some of the early season results suggest. Don't forget that Daniel Ricciardo won in Monaco despite an MGU-K failure last year, so in the next two rounds Red Bull will look to secure some serious silverware.
Renault
What's the problem?
We are now in the fourth season of Renault's five-year plan and it was meant to be the one where it closed the gap to the top three. But despite significant investment in its headquarters over the last few years, it has not yielded the results the team was expecting on track. And with one of the most exciting driver line-ups on the grid, the team can only look internally for what is going wrong.
What to expect
The team claims to have a "number of reasonable upgrades that are positive". They will include front wing upgrades, changes to the rear of the car and some mechanical tweaks to help the drivers find the right balance.
What they say
Team principal, Cyril Abiteboul: "The start of the European segment of the 2019 Formula 1 season is an opportunity for us to reset. Overall, it's been a tough start to the year and the Azerbaijan Grand Prix capped off a run of results that fell short of our expectations. We know we are capable of much more and we need to target clean weekends and races to make the most of our potential.
"To do so, we have work to do on all sides of our operation; chassis and engine on and off track, and work with the drivers to allow them to reach their respective capacities. We are motivated as ever to strive for more and we aim for a full recovery in competitiveness in Spain."
What we say
After finishing fourth last year, Renault should have been aiming to close the gap to the top three teams. By almost every metric they have failed in that goal at the opening four races while also encountering continued reliability concerns with the MGU-K.
Perhaps most worrying of all is the team's performance relative to customer team McLaren. We shouldn't play down McLaren's recovery over the winter, but when you consider where the two teams were at the end of last year, Renault appears to have fallen behind.
But there is still a belief at Renault that the results do not line up with the true performance of the car. A return to familiar territory in Barcelona could be just what the team needs to get this year's Pirelli tyres in the right operating window and return to the front of the midfield pack.
Haas
What's the problem?
Haas showed promising pace throughout pre-season testing but has struggled to realise that in races due to problems maintaining tyre temperature. Pirelli's 2019 tyres have a thinner tread than previous years and that makes it harder to retain the necessary temperature to get the compound working. Oddly, Haas seems to be struggling more than most to find the right setup to combat the issue.
What to expect
A fresh delivery of new bodywork parts will come from chassis manufacturer Dallara this weekend and not a moment too soon. Romain Grosjean has suggested something verging on a B-car but a more detailed list of the new parts is provided by team boss Guenther Steiner below.
What they say
Guenther Steiner, team principal: "We're bringing our first upgrades of the year. A lot of parts on the car will change - the front wing, the floor and a lot of the smaller parts, like mirrors. It's a quite significant upgrade.
"The hope is that it all works as it did in preseason testing. We've obviously lost a little bit of confidence after the last three race weekends, but we haven't lost it completely. We're just careful to make predictions. We are cautiously optimistic."
What we say
Haas' problem is very specific and if it can find a solution to keep the temperature in the tyres then it should unlock a lot of performance very quickly. It is not alone in struggling with the 2019 rubber, but perhaps the team's lack of simulation tools compared to its rivals has made it difficult to find a solution.
The drivers report that the problem escalates rapidly after a handful of laps as the tyre surface starts to grain and performance and temperature spirals downwards. On the plus side, Barcelona is a high-energy circuit, which combined with sunny weather, should make it much easier to generate and retain temperature. However, Haas will still be keen to find a long-term solution with the low-energy tracks of Monaco and Canada following in quick succession.
Williams
What's the problem?
Where to start? In testing the team missed the opening two days when the car turned up late and it has been playing catch-up ever since. That wouldn't be a disaster if the car was quick, but as of qualifying in Baku it was still five seconds off the ultimate pace.
What to expect
The team says it has a number of test items for Spain but will only focus on ones that offer an advantage for this weekend on Friday before completing some tests focused on longer-term performance at the two days of testing after the race.
What they say
Deputy team principal, Claire Williams: "We haven't had the best year, clearly everybody has seen that. It started with not getting our chassis to testing, and we've had to really play catch up off the back of that. So we are now in a position where we have all our race quantities, we have the quality on those race quantities that we needed, and now we're looking to bring the upgrades that have literally been sitting on a shelf as we've cleared the backlog out of manufacturing. So there is some light at the end of the tunnel.
"We're doing a lot of work back at Williams. If anyone thinks that we're just hoping for a miracle or that things will just go our way at some point, that's not the case -- a lot of work has been going on to make sure that we put ourselves in the right position."
What we say
One round of updates is not going to come close to solving Williams' problems, but a positive step towards the back of the midfield is essential to keep spirits high at the team. The updates that come in Spain will be ones developed earlier in the season/pre-season and will not necessarily represent the reshuffle going on at the team under returning technical boss Patrick Head. In George Russell the team at least has a shining light who is likely to get the most from the car in what remains a very difficult situation.