Lewis Hamilton lost a surefire victory in the Monaco Grand Prix after a bizarre decision by his Mercedes team. But what were the circumstances that led to the mistake? Adam Cooper explains...
Not for the first time, the Monaco Grand Prix was turned on its head by some late drama.
In 2011, Vitaly Petrov's crash led to a red flag which ruined a potentially fantastic climax as it meant everyone could switch to new tyres, so we didn't see how the closing laps would have unfolded for the top three drivers, each of whom had run different strategies.
This time around Max Verstappen's accident had the opposite effect, turning what had developed into a demonstration run for Lewis Hamilton into an extraordinary drama that gave us an exciting eight-lap sprint to the end.
The first part of the race could not have gone any better for Hamilton. After just five laps he was already 2.3s ahead of Nico Rosberg, and by the time the German pitted on lap 37 the gap was 7.4s.
Hamilton came in the next lap – one short of half distance – to give himself what should have been a straightforward 40-lap run to the flag on a set of new soft, prime tyres.
Hamilton didn't simply consolidate his lead, he extended it, and indeed by lap 63 he was 19.6s ahead of his teammate.
However, at Monaco you are always in the hands of the gods, as it is a venue that tends to produce drama, and very often in the closing laps. It was while he was on his 64th lap that Verstappen crashed at Ste Devote, and F1's first Virtual Safety Car was called for.
Like all the other drivers Hamilton slowed as required, and on that lap he lost around 14s relative to his previous laptimes, crossing the line with a 1m33.047s lap. His pursuers spent more of that lap at the slower speed, so by the time Rosberg crossed the line the screens suggested that he was 25.7s behind Hamilton.
By then race control had decided to turn the VSC into a regular safety car (the VSC was only in place for 30 seconds), something that the teams knew could happen. Initially at least, it doesn't make any difference to the drivers, who run at the same speed in either case.
It was at this stage that on a giant TV screen Hamilton caught a brief glimpse of the Mercedes crew standing in the pitlane, the guys having dashed out 'just in case', as is the usual routine.
He knew he wasn't making a pitstop, so his immediate conclusion was that Rosberg had, and that quite possibly Sebastian Vettel and other top runners had too.
His first thought was that when the cars were released after the safety car he could find himself stranded on old soft tyres – with low temperatures and pressures – with Rosberg heading a gaggle of rivals on supersofts. At this stage there were still some 15 laps to run, and thus quite a long time for him to hold out.
Hamilton thought Rosberg had stopped
That's what instigated a conversation with the pit wall in which he expressed his concerns about the tyres. It's here where there appears to have been a miscommunication – Hamilton thought Rosberg had pitted, and the team didn't realise that's why he was so agitated about the tyres.
They were suddenly not working from the same script.
Instead of reassuring him that neither Rosberg nor Vettel had pitted, the team heeded his tyre concerns. They did the sums and decided that there was sufficient time for him to pit and resume still safely ahead of Nico and Vettel.
In effect there was nothing to lose – it would give him a little extra comfort zone for those last few laps, and probably allow him to pull away from Rosberg once again, since the German would still be on his well worn softs, and stop any chance of the two of them getting into a fight that could end in tears.
In theory you could view the decision to stop as a safe, conservative choice.
"You rely on the team," said Hamilton. "I saw a screen, it looked like the team was out and I thought that Nico had pitted. Obviously I couldn't see the guys behind so I thought the guys behind were pitting.
"The team said to stay out, I said 'these tyres are going to drop in temperature,' and what I was assuming was that these guys would be on options and I was on the harder tyre. So, they said to pit. Without thinking I came in with full confidence that the others had done the same."
What you have to remember that even at safety car speeds a lap of Monaco passes very quickly, and the tyre conversation, the calculations and the decision to pit all happened in a matter of seconds. The big problem was that in the Swimming Pool area Hamilton caught up with the safety car, which had been busy waving other drivers through.
He had to slow to Bernd Maylander's speed for a couple of corners, while Rosberg was still going as fast as he was allowed to under the rules – and that was a crucial difference. Right at the end of the lap, just before he was due to pit, the gap had shrunk.
The problem was simply that for some reason the Mercedes strategy management system didn't recognise that, even though, as Toto Wolff noted, the final confirmation to come in was made "50 metres" before the pits.
Realisation hits Hamilton...
Only when he came blasting out of the pits – and saw Rosberg and Vettel passing by on the track – did Hamilton realise what had happened. The team had got its sums very badly wrong.
"The verdict is that often in life simple things have a big impact," Wolff told Motorsport.com. "And in that particular case the system showed us wrong data, and based on those data we decided to pit. We thought that we had a gap, but we didn't have a gap, and because in Monaco you have no GPS it makes the whole thing more complicated.
"He thought that we had pitted Nico, but he didn't realise the others didn't pit, he didn't see that. Our data said we had the margin, and when he said the tyres were gone and they will not come back, it just added up to a whole lot of information, and that made us pit. But the main call was that we had the margin.
"We got the wrong call at the wrong time, him saying the tyre temperatures dropped. We thought we had a gap but the gap wasn't there..."
Wolff's reference to the FIA's GPS system – whose information is incorporated into the teams' own calculations – is an intriguing one.
It's obvious why Monaco's environment makes GPS less effective, but the FIA and the teams back it up with other sources of position information such as loops in the track (there are around 20), and dead-reckoning algorithms.
For some reason Mercedes didn't pick up on that crucial end-of-the-lap delay behind the safety car, as Wolff explains: "We thought we had 3.5 seconds on top of a normal pitstop. And that disappeared. Somewhere the data got frozen, and we have to find out where. The numbers just didn't add up any more. The safety car stopped him a little bit..."
In essence the Mercedes sums were based on Hamilton's expected VSC speed, but the presence of the real safety car in front of him at that crucial time meant that he was slower than he should have been.
It's worth noting that Hamilton's lap 65 – which basically included the pitstop – was 2m11.321s. In contrast Felipe Nasr, who came into pit entry just four seconds later, but crucially did not have to slow for the safety car, did his lap in 1m59.948s.
And Daniel Ricciardo, who came into the pits another 31s after Nasr, completed it lap in 1m59.200s. In other words, somewhere Hamilton lost around 11s relative to the time he should have done.
Forgetting the question of what the data said or didn't say, it would seem that no one at Mercedes physically saw that he'd got caught like that. The only man who knew was Hamilton himself, sitting behind the safety car, but he didn't realise that the precious seconds he was losing were so crucial.
At least a bit of that time went astray in the pitlane itself – his first stop had a pit time of 24.181s, and the second was 25.495s, so some 1.3s went just there, probably as he was held for Nasr passing by. Certainly enough to have got him out ahead of Vettel, if not Rosberg...
Vettel not a threat
It's worth noting that Mercedes had no reason to fear a Vettel pitstop, because Ferrari had decided straight away that the German should stay out.
"We were nervous at the beginning thinking about them pitting," said team boss Maurizio Arrivabene. "We were looking at the window, and at one stage the guy working for us on strategy said, 'Stay cool, they are doing a kind of show, and we stay out.' In any case he said. 'If they come in, we stay out.'
"He was really, really straightforward on this, and he was right. I know that we were lucky, I'm not telling to you something different, but in my opinion they were a bit too much convinced about their power. I recognised that they are very intelligent, they are stronger than us, but this time we were smart..."
"We are all humans," said Wolff. "Sometimes you need to make decisions within a fraction of a second, and this time we made a decision and it was the wrong decision. We have to analyse it properly, see how we can avoid it in the future, apologise to Lewis, and apologise, and apologise."
In the end it was a self-inflicted problem for Mercedes, especially given that the stop was so unnecessary.
Niki Lauda summed it up best: "There was no challenge, there was no stress, there was confusion among the strategy people about what to do, and this is the end of it.
"We have to analyse it first and then see what we can improve on these matters. I feel sorry for him because we screwed his race up..."