Why McLaren is returning to the partner it had to leave

The McLaren-Mercedes combination will return to Formula 1 in 2021 after a six-season break, in an unlikely reunion that we never thought we'd see.

But Formula 1 never fails to surprise, and as McLaren itself taught us when it rehired Fernando Alonso, anything is possible if both parties see that there's an advantage to be gained, and there are favourable sporting and commercial implications.

The deal is nevertheless somewhat unexpected, given that Renault has made solid progress with its power unit over the past couple of years and, as sole customer, McLaren appeared to be in a good position.

The Woking team's original divorce with Mercedes occurred in two stages. The first step happened over the course of 2009, as the pacesetting Brawn GP team outran the Mercedes-backed McLaren with the same engine to win the world championship. At the same time there was a clash between the road-car ambitions of Ron Dennis and those of 40% shareholder Mercedes.

Mercedes motorsport boss Norbert Haug convinced the Daimler board that buying Brawn and creating a full Silver Arrows works team was the way to go - and plucking Michael Schumacher from retirement was the icing on the cake.

Once the shareholding arrangement had been unravelled McLaren had no choice but to continue as a paying customer of Mercedes. Dennis and his fellow owners began searching for other options. They were determined to find a new works deal, with all the support that entailed.

The idea of a reunion with Honda emerged, and in May 2013 a deal was announced, to start in '15 - the second year of the V6 turbo-hybrid formula.

McLaren thus went into the first season of the new rules still using Mercedes power, and found itself left far behind the dominant works team. Honda couldn't come soon enough, it seemed. At Suzuka in 2014, towards the end of the team's long stint with Mercedes, Dennis made his feelings known, citing the huge performance gap to the works team that year.

"My opinion, an opinion held by many people in our organisation, is that you have no chance of winning a world championship if you are not receiving the best engines from whoever is manufacturing your engines," he said.

"A modern grand prix engine in this moment in time is not just about sheer power, it's about how you harvest the energy, it's about how you store the energy, and effectively if you don't have control of that process - meaning access to source code - then you are not going to be able to stabilise your car in the entry to corners, etc, and you lose lots of lap time.

"So even though you have the same brand of engine that does not mean you have the ability to optimise the engine. So you've got to start by putting yourself in a position where you have the best engine available. That's what we've done for the approaching years."

The source code phraseology was a little anachronistic, but he'd made his point - we don't get the same ultimate performance as the works team. Toto Wolff was not impressed.

The Honda relationship was ill-starred from the start, and it was all too easy to suggest that McLaren would have done better to stick with Mercedes. Meanwhile Dennis was ousted and succeeded by Zak Brown.

In 2017 McLaren's owners began looking for a way out of the Honda deal. Given Ferrari a non-starter for obvious road-car reasons, and Mercedes giving a clear no to a reunion, Renault was the only option. It was a handy marriage of convenience for both parties.

The 2018 season showed McLaren that its problems were not just the fault of Honda, and prompted the start of a rebuilding process that has continued into this year.

Renault wanted closer co-operation in areas such as non-listed parts, and was willing to share a gearbox. Confident in its ability to go it alone, McLaren had no interest in such a route

From the outside it has appeared to work well for both sides - especially at a time when discussions over the future have taken centre stage, and teams are inevitably splitting into groups over certain issues. A Renault and McLaren alliance had at least some influence. However, the fight for fourth place on the track between the two parties has inevitably made things a little awkward.

Meanwhile, since his arrival earlier this year Andreas Seidl has played a major role in reviewing every area as McLaren looked for ways to make further progress. It was logical for the German - who was previously a hands-on BMW F1 engineer - to look at the power unit. Could McLaren do better for 2021 and beyond? Able to step back from any historical political considerations, Seidl determined that on a balance of reliability, performance and likely progress over the next few years, Mercedes was the better bet. It's that simple.

"I asked him when he joined, 'What to do we need to do to get back to the front?'" says Brown. "And he's quickly come back with recommendations like the new windtunnel. He led the decision here on the power unit. It was of course a group decision, but one that was driven by Andreas.

"We started in the middle of the year, Andreas and I, discussing what we wanted to do in the future, we knew we wanted to make a decision coming out of the summer break. Obviously we speak with Toto on a regular basis with all that's going on in the sport, so it was early summer when we started having early conversations, and we concluded the deal recently."

Brown is adamant the deal is about pure performance: "When you look at Mercedes-Benz they have been the benchmark in the hybrid era as a power unit provider both in power and reliability.

"And of course the racing team itself is the benchmark in this decade, so to have what we believe is the best engine behind our race car and ultimately chasing what we think is the best team in F1 at the moment is a good place for McLaren to be in our desire to get back to the front."

Rules ensure engine hardware has to be the same, but the doubts are always there - hence Dennis's "source codes." Can a customer team really challenge Mercedes?

Significantly, Renault's post-2021 proposal to McLaren was very different from the straight engine supply deal agreed with Mercedes.

Renault wanted closer co-operation in other areas, such as on non-listed car parts, and was even willing to share a gearbox. The manufacturer viewed that as a variation on the Ferrari/Haas deal - but with two "equal partners", helping each other to progress while keeping costs down. Confident in its own ability to go it alone, McLaren had no interest in such a route.

"The world of F1 is going to change in 2021," says Brown. "And I think that's where we are focused now with this decision, and I think some of those areas in which you can collaborate today, you're not going to be able to do in the future.

"McLaren want to stand on our own two feet and be an independent team, as we always have been. So we're going to continue to work in that direction, and I think the regulations are going to support that type of independence, maybe more so than today."

In any engine supply situation in the background lurks the question of engine parity. The rules now ensure that hardware has to be the same, and works teams can't be a spec ahead. But the doubts are always there about ultimate qualifying modes and so on - hence Dennis's "source codes." Can a customer team really challenge Mercedes?

"I'm very confident that Mercedes supplies [equally]," says Brown. "You can look at the telemetry, it's clear that's what in Mercedes' grand prix cars is the same in the Williams and Racing Point cars. If we do a very good job with our team, execute, our drivers do a good job, then I think we can. But I think you're going to have to be on your A game.

"We're looking forward to hopefully progress to a point where we're ultimately battling Mercedes. I don't think that's going to be very soon given the size of the gap. Competition is a good thing."

What's in this for Mercedes? In simple terms, an extra customer means a significant chunk of money is going into the Mercedes pot, or more specifically that of its High Performance Powertrains division at Brixworth. Any such influx of funding keeps the beancounters happy.

And while there is some overlap in the chase for wealthy car buyers between the top-of-the-range AMG models and the cheaper McLarens, that's not seen as an issue.

One intriguing aspect is that the deal has happened just two years after a request from McLaren was rejected - and the absence of the late Niki Lauda from the Stuttgart camp has played a role in that.

"Niki and I disagreed on the engine question," says Wolff. "He was very much in favour of supplying Red Bull back in the day. We were in the early stage of finally having a team that started to win, and I was against it. When the decision came up to supply McLaren a few years ago Niki said, 'Well you gotta stay true to your opinion back then and concentrate on the works team'."

Would Lauda have agreed this time around? Sadly, we'll never know. Wolff insists that with 2021 approaching, other factors have changed.

"I think the situation today is different," says Wolff. "The 2021 regulations look totally different and will change the landscape. And in this new day and age there needs to be an emphasis on the bottom line, we need to look at numbers, also in the same effect I don't believe there are big downsides."

Wolff is adamant that McLaren can expect parity. So that begs the question, given that the future budget cap is designed to rein in Mercedes (and others), is a resurgent McLaren potentially a threat if, as Brown suggests, the team is on its 'A game'?

"A new era is going to start in 2021 with compressed grids with more competition," says Wolff. "And we believe that from a power unit side there is more learning for us in this exercise, with having more competitive customers adding to the two that we have. And we rate McLaren strongly.

"The steps that Zak and Andreas have initiated certainly already look very promising. The advantages outweigh the potential deficits of fighting a hard competitor like McLaren in the future."

Supplying three customers is a stretch, even for Mercedes. Brixworth did it in 2015, when it had a one-year relationship with Lotus, and again in '16 with Manor. The second arrangement was supposed to continue into the following year, before the team collapsed.

However, even a couple of years ago Mercedes still had an advantage on the engine side, and thus some margin in the development race. Latterly all three of its rivals have been pushing hard, and Ferrari has jumped ahead.

Some have interpreted Mercedes adding a customer as the first step towards the withdrawal of its works team, but Wolff insists "the two are not linked"

Now there's even more of a premium on getting the latest incremental gains into the next spec and onto the track. The more cars you have to supply, the more challenging that is.

When the latest Phase 3 engine was introduced across the six cars at Spa there were no spares available to immediately replace the units that failed on Sergio Perez and Robert Kubica, whose Williams only received a new unit in Russia.

Having stayed loyal through the years, Racing Point and Williams have both been given pause for thought by the news that McLaren is back in the fold.

One logistical upside is that from 2021 there are restrictions on dyno usage, and thus some of the capacity that would have been used on the engines that would have been used up in the factory can now be diverted to supplying McLaren.

"I think the situation has changed a little bit," says Wolff. "We were always strict straight from the beginning that we said we want to give 100% concentration on our works team. Then we stepped a little away from that by supplying Manor, so we had three customers back in the day, and we actually learned, we realised that it was an advantage having more power units out there.

"There's maybe a process and logistic question, because everybody needs to be supplied at the same time, but I think there is more upside in it going forward. Then of course there is a financial upside, so it's a cashflow question which is helpful on the power unit side.

"So overall, many pros. There is one risk in this, that if McLaren does a good job, they will push hard, and maybe benchmark us in a way to say 'OK, that's the same power unit and you guys are not doing a good enough job'. But where we are now after seven years in the hybrid era we are ready for that step."

Some have interpreted Mercedes adding an extra customer as the first step towards the withdrawal of its works team, but Wolff insists "the two are not linked" and there's no long-term plan to become purely an engine supplier.

Brown has complete faith in McLaren's new partner, and all seems to be rosy. What remains to be seen is whether the rekindling of this relationship is the step that finally returns McLaren - without a win since 2012 and a podium since '14 - to F1's forefront.