What are F1 flexi-wings and why do new FIA tests matter so much this season?

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BARCELONA, Spain — One of Formula One’s buzzwords is back in the news ahead of this weekend’s Spanish Grand Prix: flexi-wings.

The aerodynamic design feature became a key detail of the 2024 season, so much so that Red Bull and Ferrari raised concerns about McLaren’s and Mercedes’ wings, feeling their rivals were gaining from a gray area in the rules.

The FIA declared there had been no rule breaches in September, a few days after the Italian Grand Prix, but McLaren was asked to adjust its rear-wing design several weeks later, following the race in Azerbaijan.

There, the rear wing on Oscar Piastri’s race-winning car appeared to flex at top speed — opening up a gap that in theory boosted the McLaren’s pace and was dubbed a ‘mini-DRS’. The team’s rear-wing design passed all required flexibility tests at the time, meaning it technically was legal. McLaren, though, claimed it had “proactively offered to make some minor adjustments to the wing following our conversations with the FIA.”

A wing’s flexibility has an impact on a car’s aerodynamic performance, as it can reduce the drag on the straights, when the rear wing flexes, or increase downforce at corners, when the front wing flexes more toward the ground. Both would make a car faster. It’s also been an area that teams have looked to exploit in search of speed gains across F1 history.

But, in a bid to reduce the controversy on the topic during the 2025 campaign, a technical directive was issued by the FIA in the offseason. This declared that the rules would be tightened even further around the flexibility of the front and rear wings, with stricter tests happening at the Australian (rear wing) and Spanish grands prix (front wing).

The big question about this weekend’s tests in Barcelona is how this will alter the competitive picture — if at all.

The rear-wing tests meant the rules have remained static on this part all year, but the front-wing changes were unusually delayed until a third of the season had passed.

“Barcelona is on the calendar of everybody in the paddock, with the new regulation for the front wing,” Ferrari team principal Fred Vasseur said. “We have been working on it for ages now. This can be a game-changer for everybody, because we don’t know the impact on every single team.”

What are flexi-wings?

Put simply, this is how much either wing on an F1 car flexes under the load of air moving over their surfaces while running on track. This always happens, but there are limits allowed under the regulations.

Flexing on rear wings was addressed in changes to this year’s regulations. Initially, the distance between the flap and mainplane couldn’t vary more than 2mm when 75kg of vertical load was applied to the rear wing.

FIA single-seater department director Nikolas Tombazis said in an explainer distributed by the governing body ahead of this weekend’s race that, “The 2025 regulations were designed to counteract the so-called ‘mini-DRS effect’ that became quite a talking point in the autumn of last year. That test was applied from the start of the season, but it soon became apparent it was insufficient.”

Following the Australian Grand Prix weekend, where special cameras were fitted to the cars to monitor the wings, further rear wing tests were carried out at the following two races in China and Japan. Rear-wing flexibility — between the flap and the mainplane — was reduced from 2mm to 0.75mm in China and to 0.50mm in Japan.

This issue also flared up in 2021, when the FIA issued a technical directive stating that higher load values would be placed on rear wings for a tougher test. This was the main element a few teams raised issues about that season – with the main arguments flowing between Red Bull and Mercedes, which were battling for the world titles then.

The FIA technical directive, though, did not accuse any of the teams of wrongdoing. Similarly, this season, none have failed the deflection tests. McLaren team principal Andrea Stella claimed flexi-wings have “nothing to do with the reason why McLaren is very competitive.”

Given any design changes required to pass the new tests will mainly involve strengthening internal structures to reduce flexing, it is not expected that the wings will look significantly different in Barcelona to how they did at previous races this year.

Why are the front-wing tests only happening now?

The simple answer is that development of such complex and important car parts takes time.

At a few races last year, such as the Belgian Grand Prix, cameras were also placed on cars to observe the wings, and it was determined that the tests needed to be strengthened.

Considering how late the FIA came to this conclusion — it initially indicated in late 2024 that it would not be making technical rule changes for 2025 — there was the potential that teams could incur an extra cost if they had to scrap their existing front wings. Thus, the governing body opted for a “deferred introduction,” Tombazis said.

Two key parts of the front wing are being analyzed: the bodywork flexibility and the flap flexibility, both of which fall within the regulations.

For the bodywork flexibility, the vertical deflection cannot exceed 10mm when vertical load is on both sides of the car and cannot exceed 15mm when it’s applied to only one side. Previously, 15mm and 20mm for each respective test were permitted.

As for flap flexibility, the regulation states the following for the flap flexibility for the front wing: “Any part of the trailing edge of any front-wing flap may deflect no more than 5mm, when measured along the loading axis, when a 6kg point load is applied normal to the flap.” That 5mm has now been changed to 3mm.

How do the tests work?

The vertical load test will be conducted on each car in the FIA garage in the Barcelona pit lane.

The rear tests are primarily aimed at ensuring no team continues gaining from a ‘Mini-DRS’ effect of wing flexing (Giorgio Piola Design)

As the illustration above shows, a single bar is placed across a car’s rear wing or two bars (see below) are arranged across a front wing. Two blocks of 3D printed plastic composites, which are made by each team and weigh up to 2kg, are placed across the wings and weights are added to the side of bars to force these blocks downwards onto the wings at a load of up to 100kg when the test is taking place. The amount they flex is then measured.

The FIA can test either both sides of each wing or just a single side using this apparatus — around the new tolerances. Again, for the rear wings, this is 10mm permitted when the vertical load is on both sides of the car and 15mm when the force is applied to only one side. For the front-wing flap, this is now down to 3mm of flexing.

The new restrictions on front-wing flexing are the hot-button topic at this week’s Spanish Grand Prix (Giorgio Piola Design)

As has always been the case with such static tests, wings can in theory comply with load tolerances and then still flex more while out on track, given the high speed of the air passing over their aerodynamic surfaces.

This is the technological game the teams are playing, but the new tests are intended to end the current debate about flexi-wing technology before moveable chassis parts being included by design on the new 2026 cars means that, in theory, this technology becomes less significant next season.

This season, you can get closer to the F1 action by joining The Athletic’s Formula 1 WhatsApp channel. Click here to join or search for The Athletic | F1 on your WhatsApp.

(Top photos: Sipa USA, Giorgio Piola Design; design: Dan Goldfarb)

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