“An enormous task”: How McLaren crammed a Mercedes into a car built for a Renault

2021 F1 season

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When the pandemic hit last year, Formula 1 took the sensible decision to postpone the costly introduction of new technical regulations for 2021.

Teams would continue to use their 2020 chassis for another year, but were allowed to make limited changes to them defined by a system of ‘tokens’.

There was one snag: McLaren had already signed terms with Mercedes to switch to their power units in 2021. Delaying that deal was not an option, so the FIA granted them leeway to make the changes they needed to replace their Renaults.

But even having been granted that vital concession, McLaren still faced a substantial technical challenge. Moreover, they had to tackle it under the ongoing work restrictions enforced by the pandemic, which limited direct contact with their new power unit suppliers.

Nonetheless, technical director James Key said the task had been “a very enjoyable challenge from a technical point of view” which the team had learned from.

Daniel Ricciardo, McLaren, Silverstone, 2021
McLaren were first to run their new car for 2021
“We started with having to kind of phone each other up over a screen and communicate via email,” he told RaceFans in an exclusive interview. “We couldn’t get together and discuss it between us or with our colleagues at Mercedes. It all had to be done from home and remotely in a very digital way.

“I think we learned how to work in quite different ways. Stepping back and looking at it, I think it was an enjoyable challenge for everyone and it produced some efficiencies we probably didn’t know existed before with having to work in a slightly compromised way. So that was actually a positive that came from that in many ways, one I think everyone involved can be proud of.”

Other teams used their two development tokens to introduce new noses or similar limited changes. But McLaren were looking at major surgery at the back end of their Renault-powered MCL35 to transform it into an MCL35M – the ‘M’ for Mercedes – while “trying [to] respect the homologation rules that we had.”

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“The chassis were homologated last year,” Key explained. “Effectively, everything behind the driver is what had to change.

The Renault power unit differs markedly from Mercedes
“So you think what you’ve got: You’ve got the front of the engine, the oil tank design which is typically some of the bigger volumes there, the location of the compressor we know is different, the installation of the energy store is different from one engine to the next. So all of those things have implications on the back of the chassis. Even certain types of pipe routing and high voltage cable routing will have implications.

“So all of that detail is different. That really necessitated the whole fuel cell area and everything after the seat back effectively has [to] be completely new.”

The changes around the engine itself had knock-on effects throughout the rest of the rear of the car which required further work.

“Beyond that you’ve got the cooling installation. I’ve worked with every power unit now, for my sins, and they all demand different things from cooling. Some have more cooling circuits than others, some combine them, there’s different targets and pressures and all sorts of things. So you have to re-learn all of that but still install it in something which looks reasonably similar to what you did last year.

“That also has a knock-on effect on the chassis. And then with the gearbox it’s about packaging space, it’s about the torsional resonances you could build up. Your ratios, of course, will be different from one engine to another and so on. So we have to try and adopt all of these things within the confines of homologation.

“Beyond that the software, the whole electrical installation is different, the steering wheels have to be rebuilt to match. It’s actually a massive list of stuff we had to do.”

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With the most work to do of any team, McLaren made sure they were first to have their 2021 machine running in a filming day at Silverstone. The positive progress continued in the truncated, three-day pre-season test. The team didn’t complete the highest mileage, but according to Key that was intentional.

The new engine “slotted in pretty well”, says Key
“I think the installation was very tidy,” he said. “The Mercedes is a great engine, they’re great people to work with.

“It’s a great engine package, it is very chassis-friendly in many respects but it did have its challenges in that it was a different philosophy to Renault. So some of the geometries or installation details which naturally complemented the Renault installation last year were just not possible at all with a Mercedes this year.”

In order to keep the FIA happy, wherever parts were changed to accommodate the Mercedes, McLaren had to show they were keeping adjustments to a minimum, and not exploiting the opportunity to add performance to the car.

“Almost all the bits we had to change had to be as similar as possible to last year,” said Key. “So normally you would take the gearbox, redesign it entirely specifically. Because that was homologated in 2020, we had to take something that existed, of course modify it to be suitable, but it wasn’t a fresh design.

“The FIA were really good with this. They recognised that there are certain things that were homologated that we had to change otherwise we couldn’t build the car. And we kept in close contact with them, they were satisfied we were doing the minimum necessary. It was a bit of a challenge for us, but not disastrously.”

In a ‘normal’ year the process would have involved fewer compromises. Nonetheless Key is satisfied with the job the team has done.

“If we’d had total independence and weren’t in this era of homologation and token spend, that sort of thing, there’s certainly things we would have done differently and probably optimised for. But considering all that, I think it’s actually slotted in pretty well.”

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Author information

Dieter Rencken
Dieter Rencken has held full FIA Formula 1 media accreditation since 2000, during which period he has reported from over 300 grands prix, plus...
Keith Collantine
Lifelong motor sport fan Keith set up RaceFans in 2005 - when it was originally called F1 Fanatic. Having previously worked as a motoring...

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13 comments on ““An enormous task”: How McLaren crammed a Mercedes into a car built for a Renault”

  1. “We started with having to kind of phone each other up over a screen…”

    Haha, it’s called a “video call”. You would have thought these F1 teams would be up on their technology right ;)

    Seriously though, I’m surprised the steering wheel needed so much work. I would have expected with the standard ECU the integration of the engine functions would all operate the same way.

    1. Mildly interested
      25th March 2021, 10:29

      My thoughts too re. video calling. Who says F1 is out of touch with reality?

      We used to sit and share (unclassified) design data over video >10 years ago at a large aircraft company.

  2. Just repeating I think McLaren may be a bit of a dark horse. They’ve taken a bold step with the diffuser and of course have an engine with (substantially ?) more power and arguably reliability. The fact that the computer simulations numbers seam to have been backed up by the on track time, would be why they walked away with smiles despite not having the most laps completed.

    1. I don’t know, I think they’ve probably had to ‘make do’ with quite a few parts of the car because like James Key said, they’ve only been allowed to do minimum changes due to the restrictions on development for this year. I’m sure what they’ve ended up with is not their ideal car if the restrictions weren’t in place and they’ve probably had to make quite a lot of compromises to satisfy the FIA. Personally I’d be surprised if they managed to get 3rd again in 2021, probably 4th or 5th is much more likely I’d have thought.

      1. @t1redmonkey I must admit my comment is coloured by the fact I’m a Ricciardo fan.

      2. ryanoceros666
        25th March 2021, 4:25

        Last year McLaren had the best handling car. Now they’ve fitted the best engine and have the trick diffuser. I wouldn’t be surprised if we see them putting up very similar times to RB and Merc on Saturday in Bahrain.

      3. As much as I’d love it to be a great car right at the pointy end, I just don’t see it happening. Too many “make do’s” to fit in the new PU so I expect that they could possibly be less competitive even than last year.

        Good investment for 2022 though bringing in the Mercedes PU as they’ll have 12 months to fully understand its quirks and peak performance windows.

  3. I really think McLaren should have been given special dispensation re: tokens. The fact that they did their deal with Mercedes prior to the “freeze” shouldn’t mean them being penalised from a development point of view.

    If they maintain 3rd place this year – and if they close the gap to Red Bull and Mercedes – then it will be a minor miracle. If they do achieve that then we can only imagine what would have been possible had they been treated more fairly.

    1. @Sonnycrockett McLaren were definitely penalised while customer teams were allowed to use loopholes to change far more of their cars but I think McLaren were very smart last year with their car development. McLaren spent a number of races last year I believe homologating development parts for this year that even though they may not have produced a lot of benefit on last years car, they knew they would plug into this years design for a improvement. Hoping for the best for them this weekend.

      1. To your point I would argue that McLaren have been even more-so disadvantaged by the homoligation in needing to take away resources in 2020 to focus on 2021 development, at a time they were battling for 3rd against Racing Point. The RP double-podium finish in Sakhir undoubtedly made some at McLaren question their focus on 2021.

        However with the benefit of hindsight we can say the gamble paid off for McLaren in 2020 and likely will again in 2021 given their show in testing. Here’s hoping for a 3-way battle for first in the Constructors’ Championship.

  4. This weekend we will see how it works…

  5. Remember the last a team stuffed a Merc engine in chassis designed for something else?

    Reply moderated
    1. Mildly interested
      25th March 2021, 10:25

      Absolutely, but I think their “trick” diffuser was a bit more blatant. I’m sure RB are still upset that a “loophole” (shall we call it graciously) stopped them from a clean sweep of the 2009-2013 regs.

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