Who is winning F1's development war in Spain?

"Any team will always try to improve. There's always a lot of talk before we start in Europe - that's kind of been tradition for years and years. It's talk but we'll see what the end result is on Sunday. We just have to get the best out of the package and I'm sure we'll have a package to fight all the year."

Kimi Raikkonen is never particularly interested in trying to read into Friday practice form during a grand prix weekend, but the advent of new aerodynamic regulations for 2017 - and the intense car development those rules are expected to facilitate - has still thrown extra focus onto Friday's running at Barcelona, as everyone cranes to see what Formula 1 teams have done to their cars ahead of the traditional start to the European leg of the F1 season.

Mercedes and Ferrari have won two races each so far, but Mercedes has generally enjoyed a small edge on pure pace - taking three pole positions to Ferrari's one over the first four grands prix of the campaign.

These two have been the only teams in the fight, with Red Bull cut adrift as the best of the rest and the others (barring troubled McLaren-Honda and beleaguered Sauber) engaged in a typically frenetic midfield battle.

Before we delve into what we've learned from three hours of running at Barcelona, here's how the relative pace of the 10 teams stacked up heading into this weekend, based on the first four races of the season.

Average pace ranking after four races

1. Mercedes 100.019%
2. Ferrari 100.267%
3. Red Bull 101.442%
4. Williams 102.050%
5. Renault 102.230%
6. Toro Rosso 102.569%
7. Haas 102.570%
8. Force India 102.824%
9. McLaren 103.492%
10. Sauber 103.963%

All teams have upgraded their cars to some degree for the Spanish Grand Prix, Mercedes making the most visible step by substantially revising the W08 to the point where it seems only the sidepods and 99% of the engine cover look the same as before.

The reigning champion team hasn't been at its best over the first four races of the season, despite its success, struggling to work the Pirelli tyres consistently and battling to recover ground lost to a difficult second week of pre-season testing at Barcelona, where weaknesses in the car's floor hurt its pace. It has also had to put a heavy car on a diet.

The W08 is now several kilos lighter. In Spain it features a new nose, revised aerodynamic profiling behind that nose (including that shell-shaped scoop), altered suspension, heavily modified bargeboards, changes to the floor and revised brake ducts. There is also a new engine for this race, upgraded to enhance reliability.

The way Lewis Hamilton and Valtteri Bottas have started the Spanish Grand Prix weekend, it seems these changes are working well. Mercedes trailed Ferrari during pre-season testing here - admittedly using softer tyres in much cooler conditions - but led the way comfortably through both Friday practice sessions for round five of the world championship proper.

Pure pace in Spain (soft tyre)

1. Mercedes 1m20.802s (Hamilton)
2. Ferrari 1m21.112s (Raikkonen)
3. Red Bull 1m21.438s (Verstappen)
4. Renault 1m21.687s (Hulkenberg)
5. Williams 1m22.015s (Massa)
6. Toro Rosso 1m22.265s (Sainz)
7. Haas 1m22.371s (Grosjean)
8. Force India 1m22.520s (Ocon)
9. McLaren 1m22.693s (Vandoorne)
10. Sauber 1m23.082s (Ericsson)

Hamilton's three-tenth advantage over Ferrari in FP2 is a healthy starting point, especially considering Mercedes usually pulls out an extra tenth or two by cranking the engine up to full volume when it counts in Q3.

But Ferrari hasn't stood still since the last race in Russia, bringing an update of its own to the SF70H that includes revisions to the front wing, bargeboards, brake ducts and a new Mercedes-style spoiler that extends beyond the monkey seat at the rear of the car.

Both Ferrari drivers complained of enduring a difficult day, with Vettel suggesting the car was driving him more than the other way around.

"I'm struggling a bit to find the rhythm, I'm struggling a bit with the conditions, probably more myself than the car," explained Vettel, who took a trip through the Turn 4 gravel towards the end of the second session. "I didn't get everything together, I wasn't too happy, but I can feel the car is quick so that is good.

"I don't know who brought the most updates, I don't think it matters who brought the most, it matters who brought the best.

"Some are more visual than others. I'm happy with what we brought - some of the stuff you can see, some of the stuff you will not see. No secrets but usual work."

Ferrari has not shown the greatest strength in car development in recent years, something that frustrated Fernando Alonso's quest for a third world title during his stint at Maranello, but it will need to show it can go toe to toe with Mercedes in this regard as this year's championship battle heats up.

The good news for Ferrari here is that the SF70H is potentially quite a bit quicker than it showed on Friday. Taking the best sector times achieved by the Mercedes and Ferrari drivers during the qualifying simulation runs on soft tyres puts Mercedes on a theoretical best lap of 1m20.676s and Ferrari on 1m20.772s, a difference of less than a tenth.

It looks as though the lap time is in the car, it's just that both Ferrari drivers clearly struggled to string consistent laps together in FP2 compared to their Mercedes rivals.

Vettel's team-mate Raikkonen also had a tricky session, struggling with the windy conditions that caused many cars to suffer sudden snaps of oversteer at random points around the circuit.

"It was a difficult day overall, the conditions were very tricky, quite gusty with the wind especially at the end, but it was the same for everyone," Raikkonen said. "It's normal that in testing the circuit feels always very good and then you come in the summer and it's more and more slippery and tricky.

"It was a normal Friday for us, the lap times don't tell an awful lot today. Tomorrow, we have to see where we end up."

What they do suggest is that currently it looks as though form has reversed after Sochi, where Mercedes struggled to keep the ultra-soft Pirelli tyre in its correct operating window while the Ferrari gave its drivers more flexibility to work with in the range of available grip.

Certainly, the longer runs suggest Mercedes is in very good shape at the moment.

Long run pace (soft)

1. Mercedes (Hamilton) 1m26.328s (13 laps)
2. Ferrari (Vettel) 1m26.665s (4 laps)
3. Williams (Massa) 1m26.864s (6 laps)
4. Red Bull (Ricciardo) 1m27.181s (6 laps)
5. Renault (Hulkenberg) 1m27.264s (8 laps)
6. Toro Rosso (Sainz) 1m27.472s (12 laps)
7. Force India (Ocon) 1m27.966s (12 laps)
8. McLaren (Vandoorne) 1m28.234s (13 laps)
9. Sauber (Ericsson) 1m28.961s (15 laps)
10. Haas (Grosjean) 1m29.088s (7 laps)

Long run pace (medium)

1. Mercedes (Bottas) 1m26.638s (2 laps)
2. Ferrari (Vettel) 1m27.500s (7 laps)
3. Red Bull (Ricciardo) 1m28.107s (6 laps)
4. Williams (Massa) 1m28.209s (10 laps)
5. Toro Rosso (Sainz) 1m28.492s (4 laps)
6. Renault (Hulkenberg) 1m28.528s (10 laps)
7. Force India (Ocon) 1m28.612s (4 laps)
8. Haas (Grosjean) 1m28.640s (2 laps)
9. McLaren (Vandoorne) 1m29.147s (4 laps)
10. Sauber (Wehrlein) 1m29.803s (8 laps)

Raikkonen produced a particularly poor run on the soft compound, which was slower than Felipe Massa, Daniel Ricciardo and Nico Hulkenberg - albeit over a more representative number of laps (12).

Vettel's pace is artificially inflated by a low lap-count and one extra lap at the end on lower fuel. But equally, Massa, Ricciardo and Hulkenberg would likely have been slower too had they not split their running between the soft and medium compounds.

Ricciardo indicated that Red Bull has moved closer to Ferrari thanks to a decent update on the RB13, which includes revised front suspension and new bargeboards, but it seems more likely that Ferrari just had a messy day, and that Hamilton's assessment that Mercedes and Ferrari have made very similar steps forward is probably the fairer one.

"As far as I'm aware, Red Bull's not on the radar massively," Hamilton said. "So far, it's Ferrari [that we're battling with].

"The car was feeling good, the upgrades were doing what I believe they were supposed to do. The team has done a great job with the package to move forward in this fight and make us stronger.

"[But] we've all stepped forward. It's not really changed anything - the gap looks like it's within a tenth between us and Ferrari which is the same as the last race - we've both made pretty much the identical step.

"It's still very close with the Ferraris, within a tenth, so we need to stay on top of things."

Saturday's qualifying session, with the Mercedes and Ferrari engines cranked to full power and all cars running with minimal fuel loads, will of course give a clearer indication of which teams have made proper steps forward with their upgraded cars.

Red Bull does indeed look like it's edged closer to the front, on a track where it won after the Mercedes drivers took each other out on lap one of last year's race.

But even when combining Max Verstappen's and Ricciardo's best sector times the deficit is still half a second to Ferrari and six tenths to Mercedes - on a circuit where the Renault engine's power deficit is less pronounced. Engineers reckon Barcelona to be a middle-of-the-road-track for power sensitivity.

Pure pace ranking after FP2 in Spain

1. Mercedes 100.000%
2. Ferrari 100.384%
3. Red Bull 100.787%
4. Renault 101.095%
5. Williams 101.501%
6. Toro Rosso 101.811%
7. Haas 101.942%
8. Force India 102.126%
9. McLaren 102.340%
10. Sauber 102.822%

Williams looks to have slipped back a bit at present, despite some updates to the FW40 that include revised brake ducts, but extra power on Saturday combined with a cleaner run should lift Massa into his usual close fight with Hulkenberg's Renault for seventh on the grid behind the big three teams.

The Renault features new bargeboards, but the longer runs suggest it still retains a significant race pace disadvantage to its main rival.

Toro Rosso has brought what looks like the biggest upgrade within the midfield, the STR12 featuring a revised front wing, bargeboards, floor, and sporting a T-wing for the first time.

The car has completed the first four races without any updates at all, so a significant leap forward here - on a track where aero really counts - was always likely for a team that has done a good job producing a quick chassis on high-downforce circuits over the past couple of seasons.

"We've got a direction which is emerging now and this is allowing us to tune the car into where we think we need it to be," said Toro Rosso technical director James Key. "Carlos was generally happy and clear on what was going on from his side; the longer run for him looks quite promising too."

McLaren and Sauber both seem to have moved closer to the proper midfield pack, while Force India is still experimenting with combinations of older and new parts to solve the correlation problems it is having with the Toyota windtunnel in Cologne, and cure the rear instability problem that has plagued its car since winter testing.

Haas found itself in the unusual position of its older-spec car (Romain Grosjean's) outpacing the car fitted with its new development floor (Kevin Magnussen's), so whether it has made any progress at all will not become clear until both cars run the new floor on Saturday.

What is clear is that Mercedes is visually winning Barcelona's development skirmish. But unless it translates its Friday pace advantage into a decisive victory over Ferrari on Sunday it cannot claim to have out-developed its main rival.

For the sake of the world championship fight it would be good if they remained nip and tuck in all regards.