Mercedes chief strategist, James Vowles has revealed the cause of Lewis Hamilton's lack of pace in Monaco and the thinking behind his early pit stop.

Usually when Mercedes has a bad weekend it is because they are celebrating something, a la the disaster that was Hockenheim 2019, when the German team went overboard in celebrating its 125th year in motorsport, even to the point of dressing everyone in period clothing, only to have Valtteri Bottas crash out and Lewis Hamilton finish 9th after a late spin in the difficult conditions.

Granted, the seven-time world champion has his own 'off weekends', but it is rare for his team to also get it quite so wrong at the same time.

In the team's latest video debrief, chief strategist, James Vowles explains Hamilton's lack of pace over the course of the weekend and the reasoning behind the decision to pit him first despite the Briton’s objections.

Though half-a-second off Sergio Perez' pace in FP1 and 0.390s behind Charles Leclerc in FP2, Hamilton was happy at the end of the opening day in Monaco.

"His car was working well and the times he was setting would have put him fastest across those sessions," says Vowles. "As we went into Saturday, that situation inverted. Whereas Valtteri perhaps was a little bit behind him on Thursday, Valtteri was very much leading now of our two drivers."

Citing lack of grip as the issue, Vowles explains: "On Thursday we had around 47 to 50 degrees track temperature and it cooled down significantly by the time we got to Saturday, more around the mid-30s now.

"It seems we just weren't able to get ourselves into the right working regime with the tyres and one of the drivers was just slightly happier than the other. But neither was really working the tyres as effectively as we should.

"We tried a number of set-up items," he continues," but one of the issues that you have in Monaco is that it is a confidence builder. You need laps, you need consistent laps, you need confidence that the car is giving you everything you want out of it.

"If you can carry just a kilometre an hour or two more speed through turn one, two, three for example, you generate another temperature level, another degree or two which then gives you more grip through the next sequence.

"Conversely, if you don't have confidence in the car and you don't trust it, you go down the spiral in the other way and you lose grip. The setup between the two cars wasn't dramatically different as we went into qualifying and race.

"Really, what had changed is just we weren't able to extract everything from the car and the tyres as we wanted anymore."

In terms of the undercut on Sunday, which ultimately saw Hamilton lose out to Pierre Gasly, Sebastian Vettel and Sergio Perez, Vowles explains why the team didn't listen to their driver's request that he extend his opening stint.

"The problem with an overcut is that doesn't exist until Gasly stops," says Vowles. "He has to stop to present an opportunity for us to have free air in front of us.

"He already had a gap to traffic behind, the same gap that we put Lewis into and he wasn't taking it, which means he wasn't terribly convinced that they had to stop first, they were waiting for us to stop. I am fairly confident had we waited a lap or two they still wouldn't have stopped.

"That now meant that we had an opportunity, we can wait and hope that perhaps something happens to his tyres or a situation takes place, or we can take the prerogative and go for the undercut.

"We had a fear that waiting with Lewis and waiting another two laps would just put us into a situation where that gap actually got worse to Gasly.

"On our calculations, we should have come out just ahead of him," he admits, "it wasn't an easy undercut, but it was an achievable undercut". Nonetheless Gasly emerged 0.2s ahead of Hamilton.

"It was incredibly tight and close but we were wrong, we didn't undercut. The difficulty of warming that Hard tyre on the out lap was such that we didn't complete it."

Asked whether Hamilton could have gone longer, Vowles admits: "I think we could have done a couple more laps but certainly we wouldn't have done ten more."