What’s at the heart of Mercedes’ recent F1 gearbox trouble?

Mercedes has made important changes underneath the bodywork ahead of the Styrian Grand Prix, in a bid to alleviate the gearbox problems that marred last week’s Red Bull Ring race.

With the gearbox issues having been traced back to a combination of electrical noise and vibrations caused by running over high kerbs, the team faced an intense week finding a way to prevent a repeat. For Friday practice, it moved and re-routed some of the associated sensors and wiring looms in and around the gearbox and ran a range of experiments to try to better understand what is happening.

It will not know for sure it is in the clear until Sunday – and rivals will be doing everything they can to try to push the Mercedes cars to break.

Lewis Hamilton, Mercedes F1 W11 EQ Performance

Photo by: Mark Sutton / Motorsport Images

Valtteri Bottas, Mercedes F1 W11 EQ Performance, leads Lewis Hamilton, Mercedes F1 W11 EQ Performance, and Charles Leclerc, Ferrari SF1000

Photo by: Charles Coates / Motorsport Images

Mercedes first encountered the gearbox problem during Friday free practice last week and by qualifying it knew it faced a battle to survive the race. This essentially put them in management mode pretty early-on in the race, as sensors on the car started to ring alarm bells on the pitwall, in the garages and at mission control back at Brackley – firstly on Bottas’ car and then Hamilton’s.
Mercedes trackside engineering director, Andrew Shovlin, says that it’s an issue that’s “not manifesting itself as one thing,” and that “it’s basically a build-up of electrical noise that starts to interfere with the various systems”.

The description from Shovlin suggests this is a problem that builds over time, with it understood that the violent nature of the kerbs are causing the wiring looms to degrade. This then triggers the electrical interference that affects the gearbox sensors.

As James Vowles, Mercedes strategy director, explained: “The Austrian circuit is very, very aggressive, especially with the kerbs. You have to use the kerbs in order to get the lap time out of it but those kerbs are also generating a lot of vibrations in the car and a lot of load in the car.”

But, from a technical standpoint, are the kerbs really the trigger point and could there be a further factor that has come into play?

If we rewind to a video that Mercedes put out when it launched this season’s challenger, technical director James Allison said: “The rear suspension on this car is extremely adventurous, specifically on the lower rear wishbone, where we’ve put a new geometry in there, that gives us more aerodynamic opportunity and allows us to get more downforce on the car.”

Lewis Hamilton, Mercedes F1 W11

Photo by: Andy Hone / Motorsport Images

This alteration by Mercedes has resulted in the lower wishbone being raised up off the floor, aligning it more effectively with the driveshaft fairing behind. More importantly, it clears room for better flow over that section of floor, where it has extended the ceiling height of the diffuser.

Raising the lower wishbone’s anchor point on the gearbox casing raises an interesting technical novelty that the team ran last season and appears to have tried to make further gains from this season too.

To understand how this can have a bearing, perhaps it’s worth remembering that Mercedes has what’s known as a cassette-style arrangement. This basically means that the casing and crash structure are separate entities to the gearbox itself.

Ferrari F2004 and Mercedes W04 gearboxes

Photo by: Giorgio Piola

This is not a new arrangement for the team – it’s been constantly evolving the concept since it first introduced it back in 2013, which Aldo Costa is credited for, having been with Ferrari when the Italia outfit first introduced it back in 2004. The reasons for such a solution have evolved over the years, but one of the major reasons is that it allows the team to change the casing and crash structure without suffering a penalty for changing the gearbox.

It also allows the gearbox and casing to be tested independently of one another, in order to reduce development and manufacturing lead times. It means the team has a huge amount of flexibility in terms of setup and design, with Mercedes taking another leaf out of Ferrari’s book last season, as its gearbox casing featured a solution favoured by Ferrari in 2015 and 2016, but has since moved away from.

Ferrari SF15-T gearbox and exhausts design

Photo by: Giorgio Piola

This extreme packaging solution saw Ferrari, and now Mercedes, use four mounting studs between the power unit and gearbox casing rather than six, in order to shape the casing so it can repackage the exhausts. The knock-on effect is that the surrounding bodywork can also be shrink wrapped more tightly and an aerodynamic advantage be gained.

These gains don’t come for free though and mean that the casing must be pushed even closer to its structural limits, as it is missing the middle studs that would ordinarily help with the stress and torsional loads that it must endure. 

The following illustration of Mercedes 2014 power unit shows where the studs would ordinarily be placed, with the middle ones (blue arrow, below left) removed to make way for the repackaging of the more expansive exhaust solution now favoured (2019’s arrangement on the Racing Point RP19, below right).

Mercedes PU106 powerunit, pipework from compressor at the front of the ICE suggests Williams FW36

Photo by: Giorgio Piola

Lance Stroll, Racing Point RP19, returns to the pits without an engine cover

Photo by: Mark Sutton / Motorsport Images

Interestingly, the FIA has recently moved to remove some ambiguity in the wording of the regulations surrounding this for 2021, making it obvious that four or six studs may be used, where it previously appeared that you must have six.

For those wondering why Racing Point didn’t suffer the same fate during the first race of the season, it’s likely due to the fact that while it buys some of its components from Mercedes, it still produces some of its own. In keeping with its quest to mimic last year’s Mercedes, the RP20 follows the same path as the W10 when it comes to its rear suspension geometry, with the wishbone mounted at a different angle to the W11.

Sergio Perez, Racing Point RP20

Photo by: Mark Sutton / Motorsport Images

Triple whammy

Combining these two technical novelties on the W11, you’ll see that the lower wishbone is now fixed to the gearbox casing in a higher position and at a point further from the lower fixing studs. 

Sparks from the rear of Valtteri Bottas, Mercedes F1 W11 EQ Performance

Photo by: Charles Coates / Motorsport Images

Having altered the load paths, this change, along with the shockwaves put through the car by the kerbs around the Red Bull Ring, could be contributing to the resonance issue that has a harmonic effect on the car’s sensors and electrical components and can ultimately affect the operation of the gearbox.

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