What went wrong in Mercedes' pit stop?

Even seven-time world champions make mistakes -- and the problem with being the best team on the grid is that when mistakes happen, they tend to be huge.

As was the case on Sunday evening, when a simple mix up of identical-looking tyres cost George Russell his first win in Formula One and Mercedes an easy one-two victory.

"Overall for us it was a colossal f--- up," Mercedes team boss Toto Wolff said live on television after the race. "I know I'm not allowed to say that but it was."

There's no point arguing with Wolff. That's exactly what it was. But while it destroyed one fairytale result by dropping Russell down the order, it manufactured another by giving Sergio Perez his first victory in 190 starts.

Below is a look at how and why the main turning point of the Sakhir Grand Prix unfolded.

What went wrong?

Put simply, a radio call to bring new tyres into the pit lane was not heard by the people responsible for doing exactly that.

Mercedes has a system whereby Russell's side of the garage (which is usually Lewis Hamilton's side) is known as the red crew and Valtteri Bottas' side is the blue crew.

Ahead of a pit stop, it is the job of Mercedes' long-serving team manager Ron Meadows to radio the crews and tell them which set of tyres to bring into the pit lane.

In this instance both cars were pitting in what is known as a double-stack pit stop -- where one car follows the other through the pits and both are serviced -- so both crews were radioed in the order "red crew standby" and "blue crew standby". But due to a problem with the radio, only the blue crew got the message and were able to react.

"We haven't had enough time to get an absolute and thorough understanding of what went on, but we have found a smoking gun and that's to do with how the radio system prioritised the messages when Ron was calling out to the crews to get them ready with the tyres for the two drivers," chief trackside engineer Andrew Shovlin said on Sunday night.

"There were a number of broadcasts at that time on the radio system, and the system knows to prioritise the messages from Rob because the most thing is that the tyres are there, more so than what a driver says or what someone else in the group might say.

"But it looks like there was a period whereby the system was deciding to let the priority message through and we missed a key bit of the broadcast, such that half of the tyre collectors [the red crew] didn't get the message and half of them did."

It should be noted that the pit stops were unplanned and were made as a reaction to the Safety Car that had been deployed following Jack Aitken's accident at the final corner. As a result, the radio messages went out at relatively late notice, almost as Russell was arriving at the entrance to the pit lane, meaning any breakdown in communication was always going to be harder to recover.

In a normal double-stack situation, you would have both sets of tyres for both cars ready in the pit lane when the first car arrives, but in this instance the miscommunication meant only six tyres turned up -- all four of Bottas' and only the rear tyres from Russell's.

It's not clear why the front tyre mechanics from the red side of the garage did not react in the same way as the rear tyre mechanics, but it is thought the rear tyre guys simply reacted to what they saw going on around them among the blue mechanics. Of course, had the message gone through on the radio, all four of Russell's tyres would have been ready

When Russell stopped in the pit box from the lead of the race, the correct rear tyres from his own set were fitted but Bottas' front tyres were also bolted on.

Mercedes' head tyre technician realised the error pretty much as it happened and radioed chief strategist James Vowles to say there was a problem, but given the speed of an F1 pit stop there was not enough time to react before Russell was heading down the pit lane with Bottas' front tyres attached.

A logo is spray-painted on the tyres in either red or blue to avoid confusion and they are kept in tyre blankets with different colour writing on them, but the mechanics on each corner of the car who actually bolt the tyres on had no time to check as they tried to service two cars in record time and at very late notice.

By the time Bottas pulled up in the box, Russell's front tyres had arrived in the pit lane and were briefly fitted to the Finn's car before the error was realised and they were taken off again. At that point the team could have held Bottas in the box and fetched another full set of mediums from the garage, but instead made the call to refit the hards he was on and send him back out.

Given that his front left brake had caught fire in the delay, it was no surprise that there was some urgency to get him going again, but Bottas really struggled on the old set of tyres for the rest of the race and, with hindsight, it would have been better to hold him longer and wait for another set of mediums.

Mercedes then had a situation whereby Russell was still leading the race but was on a mixed set of tyres. It wasn't immediately clear whether leaving him out would have resulted in a penalty, but judging by the stewards' communication later in the evening -- in which the team was fined €20,000 but Russell was not penalised -- a failure to rectify the issue would have likely led to a penalty for the driver as well.

And so, Russell returned to the pits, took on a new set of unmixed medium tyres and rejoined the race in fifth place behind Bottas, Lance Stroll, Esteban Ocon and Perez.

"It looked like we don't know what we are doing, but the issue all comes down to this root cause where we lost a key message at a key time," Shovlin added.. "We found this smoking gun, now we just need to go through the logs of how everything was working and once we have got a complete understanding of that and we have filled in some of the blanks that we are not certain of at the moment, we can then find a solution in time for [the next race] in Abu Dhabi."

Why did Mercedes pit its drivers in the first place?

The original plan for both drivers was a one-stop strategy, switching from mediums to hards midway through the race. By the time of the pit stop in question happened, the planned stop had already taken place, so at the problematic stop was completely unplanned.

But an F1's strategist's job is not done until the cars cross the line, and the main task after the final planned pit stop is to predict what might happen in a Safety Car comes out. Based on simulation software, teams know at least five laps in advance of a potential Safety Car appearance whether it makes sense to pit, and in this instance it was a no-brainer.

Such was Mercedes' advantage at that stage of the race, if both cars completed a normal pit stop they would easily retained the lead and had fresh rubber on their cars. Opting against pitting would have given the cars behind the opportunity to take on fresh tyres, also retain position, and then attack Mercedes on fresher rubber once the field had been bunched up behind the Safety Car and racing got back underway.

"It was a safety stop," Wolff explained. "We were fine on the hards and we could have stayed out but we had the gap and you do these things. You can question it but I think it was absolutely the right call."

What's more, Mercedes has one of the best pit crews in the pit lane and has pulled off a late-notice double-stack pit stop on numerous occasions.

"As a racing team you can't be afraid of doing a pit stop and you can't be afraid of doing a pit stop under pressure. We do 100s of these in races, under pressure, double-stacked, all sorts of things, and they go well and the ability to do them under pressure often wins you races.

"So it's one where you can say it was, in a sense, a precautionary stop to make sure we had the best tyres on the car and it would have consolidated the lead of the race if we had been able to perform it well. We need to make sure in understanding it, like any other fault, that you focus on root cause and not all the other noise and chaos around it."

Would Russell have won without the puncture?

Even though Russell dropped to fifth, he soon fought his way back up to second place once racing resumed after the Safety Car. Ultimately a puncture put an end to that charge, but even with a deflating tyre he was closing in on race leader Perez at a rate of 0.4s per lap and as he pealed into the pits for the fourth time in the race on lap 79 of 87 he was just 2.1s off the lead.

Perez believes he would have held Russell off as his engineers calculated that the car behind needed a 0.8s pace advantage per lap to try a move, but with the help of DRS and fresher softer tyres, Russell almost certainly would have had a go.

You could then say that Russell lost the race due to the bad luck of the puncture and everything that went before in the messy pit stop was null and void. But Mercedes confirmed Russell picked up the puncture at Turn 10, where Aitken had his accident, and the team suspects it was a result of Russell needing to drive off the racing line in the process of making up positions after the Safety Car that damaged the tyre.

Put simply, had he not fallen down the order due to the messy pit stop, he would not have been on that part of the track and would not have suffered a puncture.

The only positive for Russell is that, after a display like that, he's very likely to have another shot at victory from the cockpit of a Mercedes in the future.