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The "mini skirt" benefit behind Formula 1's sidepod shift

Ferrari's decision to throw in the towel on its in-wash bathtub sidepods means that all of Formula 1's top squads have now switched to a downwash concept.

Aston Martin AMR23 sidepods view

The change in how air behaves over the top of the sidepod may appear to be quite subtle, which is why teams have long played down the significance of the performance gain from this area of the car.

However, as McLaren team principal Andrea Stella has explained, the real gains from shifting sidepods are far more to do with how the shape of the sidepods interacts with the rest of the car rather than just what is happening in this area.

He suggests that the biggest advantage of going the downwash route is the width and shape of the undercut, which he suggests offers opportunities through the shaping of the floor to produce a less amplified version of the benefit that skirts gave back in the previous ground effect era.

Asked by Autosport to explain the key upside from downwash, Stella said: "Yeah, I wouldn't say simply downwash. I would say wide sidepods. I think it's actually the primary concept that seems to interact very well with the floor. Because the sidepods in simple terms, act a little bit like mini skirts.

"Aerodynamically these wide sidepods help the suction in the floor. So that's the concept that it looks like you can't do without if you want to maximise the suction in the floor and the load on the car. And it's very clear that everyone is converging in that direction."

Stella's reference to 'mini skirts' is about the way that the floor was sealed in the original ground effect era through the use of skirts along the bottom of the sidepods, which effectively created an area of super low pressure under the car to boost downforce.

While such a seal is not possible now, because of minimum floor height restrictions, the general theory behind what is going on with air underneath the car still holds true.

The wider sidepods, as Stella refers to them, can therefore be seen as a means to deal with the wake turbulence created by the front wheels, much like the deflectors did under the previous regulations, albeit not with as much design freedom to 'off body' the airflow.

This continues down the sidepod's surface, helping with the floor edge and having an influence over the rear wheel wake, reducing the influence it can have on the diffuser.

The solution of course is not as effective as some of the extreme solutions seen on cars in the 1980s, but any gain you can find in F1 these days is important when the gaps between teams are so small.

Ferrari SF-23 comparison Spanish GP

Ferrari SF-23 comparison Spanish GP

Photo by: Giorgio Piola

Ferrari found it pretty clear that the performance uplift coming from downwash sidepods was obvious to see in the wind tunnel, which is why it committed to a change of approach.

F1's cost cap environment means there is only a finite amount of resources at each team's disposal, therefore it takes time to cross the threshold where another solution might pay dividends.

As Ferrari's Jock Clear said: "We're not copying anyone, per se, we're looking at what they did, we're going back to our tunnel, and trying to find out if that works.

"Now, it's appeared on the car now, because it works. Ultimately, we only follow the science. And the great thing about aerodynamics, and a great thing about this sport and the reason we do it, in my case for 30 years, is because every day is different, every year is different, every car is different. And we're still learning. There are a million ways to solve the problems. And you're never going to cover all of them."

For Ferrari, just as has been the case for Mercedes, moving in the downwash ramp direction has also come at the expense of some design compromises when compared with starting afresh.

As an example, the shape and position of the inlet have been retained, whilst it has had less work to do in order to make the sidepod and floor interface work in conjunction with one another, given that their outgoing bathtub-style solution was already wide-bodied.

But that's not to say optimisations won't follow here, as there's clearly headroom to improve performance, as the likes of Red Bull, Alpine, AlphaTauri, and Aston Martin have shown with their aggressive modifications to the idea.

It's also clear that teams that made the decision to switch concepts last season, such as Aston Martin and Williams, have made structural changes this season to further enhance the new layout.

Ferrari will likely do so next season but, in the meantime, it has found a way to improve aerodynamic performance, with a deeper undercut found beneath the inlet, which is evidenced by the larger blister now needed to cover the SIS (Side Impact Structure) within.

Meanwhile, the sunken bodywork that formed the bathtub on the outgoing solution has been transformed into more of a gulley and feeds airflow into the new downwash section. However, it's worth noting that Ferrari has fallen short of widening the bodywork here and is still broadly following the in-wash philosophy it previously employed.

Ferrari SF-23 Detail

Ferrari SF-23 Detail

Photo by: Giorgio Piola

By and large, this seems to be connected to its reluctance to switch to the shelf-like engine cover solution that many of its rivals have adopted, with a more tapered bodywork layout favoured at the rear of the SF-23 in order to minimise the rear cooling outlet.

Nonetheless, it appears to be a first step in this direction that's helped improve performance and the overall driveability of the car, with Clear eager to draw attention to these factors:

"This upgrade is a testament to our aero guys to get this car to work around the chassis we have and the DNA of this car. And this is just the first step towards that.

"This has not made half a second, seven-tenths of a second difference, this is two/three-tenths at best. But the positive thing is it's two-tenths in Barcelona, and Barcelona is a circuit which really exposes a car's weakness. You can't come to Barcelona and hide."

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