The warnings still lurking for Mercedes in Japan

Although Lewis Hamilton qualified on pole and finished second in Malaysia, there can be no doubt Formula 1's farewell race at Sepang was one of Mercedes' most difficult of the season so far.

For the first time, it looked as though Ferrari had stolen a definitive march in F1's frenetic aerodynamic upgrade war. That Hamilton reverted to an older specification to limit the damage, while team-mate Valtteri Bottas endured his least competitive grand prix of the year running the new parts, indicated how many questions Malaysia raised for Mercedes.

Conversely, Ferrari's updates worked fine. The Scuderia had the fastest car in Malaysia. It could and should have won the race relatively comfortably. But a freak engine failure on both cars turned Ferrari's weekend into a nightmare, and made Mercedes look much better than it was in reality.

Hamilton headed to Suzuka for the Japanese Grand Prix not convinced he should go back to running Mercedes' latest upgrade. He is using it, because Mercedes is convinced of its potential, but that potential is clearly not easy to unlock, and Mercedes is clearly pinning its hopes on cooler conditions to prevent overheating of the tyres and make life easier in Japan.

"I think being a cooler circuit here, the car will be in a much better position," Hamilton said ahead of practice, describing the W08 as "stubborn".

"But I think Ferrari did bring quite a big upgrade in the last race, so it'll be interesting to see that properly unleashed.

"Generally the hotter places we struggle a little bit more; being that it's cooler [here] hopefully [that will] bring it back more into our window.

"There's so many factors you have to take into account - like the previous year's results, how comfortable Valtteri was, tyre temperatures, all these different things that come into play.

"While it seems clear [to use the upgraded parts again], it's not actually clear, and ultimately I want to have the best performing package of the weekend. I need it to compete with what Ferrari has brought in the last race, what the Red Bulls have been doing with their flexi wings and bits dangling off the car.

"I want to make sure I've got the strongest package to be able to deliver a blow back whenever they send one on.

"Me and the car have lots of things in common. It's got great potential but it doesn't always do what you want it to do."

Mercedes technical director James Allison is hopeful next year's car will have a "sweeter temperament", but for now the team must make do with its diva.

Certainly it's true that Mercedes tends to do better relative to its opposition in cooler conditions, and when the track has yet to rubber in. For a big clue as to how much performance can swing from race to race based on little more than track temperature, look at Haas, which was nowhere in Malaysia, but top-10 fast in the only dry practice session on Friday in Japan.

"Silverstone, we were in the top 10 in qualifying and could have gone faster, then on Sunday we were nowhere," says Romain Grosjean. "It's one day to the next, because the track temperature changes.

"In FP2 [in Malaysia], it felt amazing on the softs and I was really happy, and then we put on super-softs, really attacking, and, honestly, I thought I was on the rim - like the tyres weren't underneath [me].

"We are a little bit at the mercy of the track conditions. Brazil last year, we were 15th in FP2 then seventh in qualifying. The only difference was the cloud and a bit of track temperature."

"Me and the car have lots of things in common. It's got great potential but it doesn't always do what you want it to do" Lewis Hamilton

The contrast in conditions between Malaysia and Japan is stark. Track temperatures were in the high 30s and 40s consistently at Sepang, and the ambient was always 30C-plus from Saturday onwards. In first practice at Suzuka the track was a relatively icy 24C; the ambient barely in the 20s. That should bring Mercedes right back into play, though hotter weather is forecast for Sunday's race.

What could potentially be concerning for Mercedes is how fast Ferrari was out of the blocks on Friday, despite the vastly cooler conditions, and how aspects of Suzuka's layout mirror Sepang closely, which will expose any residual weakness in the Mercedes package.

Pure pace ranking

1. Ferrari (Vettel) 1m29.166s
2. Mercedes (Hamilton) 1m29.377s
3. Red Bull (Ricciardo) 1m29.541s
4. Force India (Ocon) 1m30.899s
5. Renault (Hulkenberg) 1m30.974s
6. Haas (Grosjean) 1m31.032s
7. McLaren (Vandoorne) 1m31.202s
8. Williams (Stroll) 1m31.602s
9. Toro Rosso (Sainz) 1m32.252s
10. Sauber (Wehrlein) 1m32.897s

"This circuit has some very high-speed, easy corners: 130R should be easy flat in these cars, which discounts it as a corner," says one senior paddock engineer. "There are two low-speed corners - Turn 11, the hairpin, and Turns 15/16, the chicane. You can't forget about them.

"The rest is true medium-speed. Although some you enter at high-speed. For example, Turn 1, you enter fast, but the Esses is medium to high. You need to pitch your car there.

"It's different to Silverstone, which is very high-speed - Abbey, Copse, Maggotts/Becketts. That's where you are grip limited. The Esses here have more of a mid-corner phase and you need a good change of direction - you need a good front end without the rear becoming too loose.

"You tend to be understeer-limited in sector one. You need to give the driver confidence to drive his way through without the front washing out or the rear stepping out, so it's quite tricky.

"If you look at sector two at Sepang, there is always a front limitation and you could hear Bottas screaming on the radio about understeer.

"In high-speed, short-duration corners that doesn't matter so much, but here the corners tend to go on a long time, sweeping from one side to the other, like Turn 5/6 in Malaysia.

"And the limitation can change from front to rear depending on the weather. You tend to be rear limited when it's hot and front limited when it's cooler. Just 10C of track temperature can make all the difference."

There are several key warnings for Mercedes here. Firstly, the fact that parts of the circuit place very similar demands on the car to sector two at Sepang, where the updated Mercedes - in Bottas's hands - was slower than both Ferrari and Red Bull in qualifying.

Secondly, how vital a good balance is to allow the driver to extract performance from the car - something that was very difficult to find with the upgraded W08 in Malaysia. And three, how a relatively small swing in track temperature in the wrong direction could throw the car totally out of whack.

These are challenges that all teams must face of course, but while the W08 proves to be so "stubborn" compared to the Ferrari SF70H and the Red Bull RB13, that makes Mercedes particularly vulnerable.

"Historically people have run low wing levels here," adds the engineer. "The basic circuit efficiency - downforce versus drag - leads you more towards taking downforce off than in Malaysia, but the difficulty is that leads to more sliding and hurting the tyres for longer in the corners, which pushes you [back] towards higher downforce.

"No-one is going to turn up with their Monaco rear wing, but teams generally end up on the higher end. Some may need to trim downforce just because of the front limitation. In the blown downforce era, Red Bull and [Sebastian] Vettel won races with smaller rear wings, perhaps because they couldn't get enough front end on the car.

"A lot depends on the tyres and the balance. The medium speed nature of the circuit pushes you towards more downforce, but car characteristics can change with updates.

"People underestimate balance. We talk endlessly about performance in F1, but if the driver doesn't have balance in the car you're fucked as well. If a driver is balance-limited it doesn't matter what you do. Very often you have to spend some more time working to get the most out of a big update package because of this."

Mercedes is certainly worried about Ferrari's potential here, and with good reason

That's why Mercedes has persisted with its aero upgrade here, confident it can find a way to unlock that hidden extra performance with a bit more understanding and fine-tuning.

Both Hamilton and team boss Toto Wolff spoke after the Malaysian GP about "the best race debrief" they'd ever had, and the aim will be to apply some of that learning immediately.

It certainly appears Mercedes has taken a decent relative step forward here. In Malaysia, the closest the upgraded W08 ultimately got to the pace in any single session was four tenths off. Hamilton lapped only two tenths slower than Vettel in the dry on Friday morning in Japan, saying the car felt "back to normal".

But if you analyse their best sectors from that opening session, which contained the only meaningful running of the day thanks to the afternoon being washed out by rain, that gap grows to 0.329s, with Hamilton a couple of tenths clear of Daniel Ricciardo's Red Bull.

It's pretty much equal between Hamilton and Vettel through sector three (130R and the chicane), which should be Mercedes' strongest given it's mostly full throttle. Through sector one (the Esses) Vettel was 0.146s faster; through sector two (the Degners, the hairpin and Spoon), the gap was 0.186s.

That's a useful advantage as things stand, and further proof of Ferrari's potency in the development race, though it should be noted Ferrari's fastest times came later in the session than for Mercedes and Red Bull.

Nevertheless, the Ferrari looked well balanced on both the soft and super-soft compounds - once Vettel had been into the pits for some early adjustments - and although longer running was limited, the higher-fuel laps we did see put Ferrari comfortably out in front.

Hamilton was 1.4s slower than Vettel, nearly a second off Raikkonen's pace, and only 0.17s quicker than Ricciardo's Red Bull - though Ferrari completed far fewer laps for comparison than either Mercedes or Red Bull did, which skews the picture.

That gap will surely reduce, but it still further indicates Ferrari is in good shape again. The Prancing Horse believed it had the fastest car in Malaysia, and surely would have locked out the front row without those engine failures.

The big question is whether Ferrari's obvious strength in long duration, medium to high-speed corners, showcased at the Red Bull Ring, masked by underperformance at Silverstone, back on display at Spa, and apparent again here, will ultimately be enough to subvert Mercedes' usual edge in the flat-out sections, particularly when the "magic" engine modes are employed in Q3.

The relative lack of low-speed corners here compared to Malaysia should help Mercedes, but it won't necessarily hurt Ferrari either. Mercedes is certainly worried about Ferrari's potential here, and with good reason.

"It looks like everything is on plan," said Vettel. "Overall the car is working, it's delivering what we expected. Now we need to make sure the results come.

"Obviously the results were not the best the last couple of races, but I think we are strong, so we have reason to be confident. I'm pretty sure on Sunday we will be able to show what we can do."

Red Bull is likely to be less of a factor here, especially if conditions remain cool. The RB13 is again looking strong in the corners, despite running less downforce than its main rivals, but leaks an estimated 0.5s on the straights here, hurt particularly through 130R, where residual inefficiencies in the engine through the transmission are exposed under severe load. Here the Renault runs out of top-end puff while the Mercedes and Ferrari engines are still accelerating.

"Our pace was pretty good, but we still need to find a good compromise with the downforce we are going to run here," said Ricciardo. "We were losing a lot on the straight and I don't think it was just engine.

"We were relatively close to Mercedes and Ferrari, so not a bad day, but we know they will always go a lot quicker, so we need to find a few more tenths if we want to battle with them in the dry on Sunday."

But if conditions are wet - possible for qualifying but unlikely for the race - Red Bull will likely be a substantial threat for pole, and that could give its drivers (particularly wet-weather virtuoso Max Verstappen) a chance to start the race with superior track position and cling on at the front, knowing the top three cars will naturally converge in performance in race conditions anyway.

But ordinarily, after the oddities of Malaysia, the Japanese GP should be a straight fight between Ferrari and Mercedes again - Mercedes pitching added understanding of its troublesome new upgrade against Ferrari's continued strong form.

Allison is certainly expecting a "50/50 slugging match" this weekend, rather than a situation where Mercedes "crushes everything in front of us", as it did at Silverstone, or ends up on "the other end of that deal", as it's done on slower tracks.

With cooler weather and a better set-up, Mercedes should be properly in the fight again, provided conditions don't become unexpectedly hot, but it's probably going to be close.

Ferrari is now confident in its potential to carry this fight right to the bitter end. There will likely be no easy rides for Mercedes from here on out.