F1 Tech | How Hamilton's disqualification revealed hidden secrets of the SF-25

A very competitive car on Friday and in the Sprint

The Shanghai International Circuit is a very complete track, with a variety of long straights, slow, medium and high speed corners where a lot of downforce is required. Due to the new asphalt, which has never been used before, Ferrari decided to adapt a two-element beam wing during Friday’s FP1: as highlighted in the drawing below, this version was the one they’ve been using since testing in Bahrain and is a medium downforce one.

The lower element is characterised by a very pronounced chord for almost its entire length, which decreases at the attachment to the endplate and to the rear structure. The design of this element represents a sort of "addition" to the upper wall of the diffuser, helping in the flow extraction. Furthermore, the upper element is characterised by a very reduced chord and an almost horizontal trend, mainly to reduce drag, while ensuring a slight increase in downforce.

In particular, this design favours the creation of a low pressure area between the two profiles, thus improving the efficiency of the rear wing-beam wing and diffuser complex (orange arrows, right hand side of the drawing below).

From the Sprint Qualifying onwards, however, Ferrari decided to adapt a single element beam wing on both cars, with the lower element identical to the one described above (orange arrow, left hand side of the drawing). This design mainly has the aim to reduce drag, improving the top speed without penalising the downforce generated.

The high level of grip generated by the new asphalt matched with hot temperature helped the less loaded cars as it provided extra grip, limiting the sliding (especially on the rear) that could have been caused by the adoption of a lower downforce set-up.

That’s exactly what happened on Friday afternoon during Sprint Qualifying: on the soft tyres, the SF-25 perfectly entered its operating window (mainly thanks to the temperature and track conditions), proving to be extremely quick. Hamilton, in fact, was very competitive in all the high speed corners of the track and especially in the complex Turns 1-2-3 section, where the high grip provided by the front end of his Ferrari made him the quickest in this section for the entire session. Moreover, the car seemed well-balanced, as the rear end wasn’t as nervous as seen in Bahrain, mainly thanks to the grip offered both by the new soft tyre and the asphalt. 

However, the car still struggled a little bit in slow- and medium-speed corners, where McLaren had the edge thanks to the better tyre management over the single lap as well as the higher level of downforce adapted on their car (the MCL39 was fitted with a medium downforce rear wing, which provided excellent grip on the rear axle). Leclerc himself denounced this problem on Thursday, before the weekend even started: “Low and medium speed seems to be the area where we need to work on a little bit more for now.”

During Saturday’s Sprint the SF-25 was very competitive, as the team adopted very low ride heights, especially on the rear, conscious that the 19-lap race and the relatively low level of fuel on board would have been an advantage for Ferrari. Moreover, Hamilton could benefit from free air which seemed to be a huge ally to not put too much stress especially on the front left tyre, which suffered from graining on almost every car. 

The scenario completely changed from Saturday afternoon onwards, as Parc Fermé was re-opened after the Sprint to allow every team to make changes on their cars. While other teams seemed to have improved by quite a big leap, Ferrari made small adjustments that didn’t translate into a big improvement in terms of performance, with Hamilton and Leclerc qualifying in P5 and P6 respectively. 

But why did this happen?

Ferrari's two worrying problems 

To answer to this question, it’s important to underline that during the first two races of the season, Ferrari had two main problems, which are related to each other: 

- the first problem has been the need for the SF-25 to run at very low ride heights especially at the rear, to make the floor and diffuser work at their best and thus generating a lot of downforce; 

- the second one is the lack of grip on the rear axle (both aerodynamical and mechanical).

For what concerns the first problem, the SF-25 needs to work at very low distance to the ground so that the diffuser generates a lot of downforce. This is a trait that was could be also seen on the 2022 F1-75, which suffered from proposing because of the low heights on the rear axle. When the TD039 was introduced in Spa in 2022, in fact, Ferrari was one of the most hit teams, as the directive set limits on plank wear, preventing cars from running too close to the ground.  

Coming back to this year’s car, the high level of downforce generated when the car is low, compensates for the adaption of less loaded rear wing and beam wing, as appeared this weekend: despite having a single element beam wing in the Sprint, the SF-25 had a very strong rear end, thanks to the load generated by the Venturi channels, which matched the load of the front axle making the car very well balanced and easier to drive. However, as soon as the car was lifted, it lost downforce and performance on the rear end, making the SF-25 pointy on the front. 

This rear instability is also related to the diffuser design. Having a look at the drawing below, as highlighted by the red arrow on the right, the diffuser shows a completely new keel shape. This year all the teams have converted to a pointed keel shape at the end of the boat section, which helps to maintain a more constant level of downforce at different heights from the ground.

On the other hand, Ferrari has decided to adapt a much simpler and rounded design, which works very well at low heights, while it’s more difficult to make it work when the car is raised. At the same time, the arrow on the left allows us to note the additional opening on the side wall of the diffuser ramp, located behind the mouse hole. The aim of this hole is to increase the flow rate towards the ceiling of the diffuser, increasing the amount of flow extracted and thus the downforce generated. 

This explanation allows us to go deeper into the second problem shown off during the first two races. The rear end of the SF-25 is probably very weak both in terms of aerodynamics and mechanical grip, as the car struggles a lot in all slow speed sections and in traction phases. The lack of aerodynamic load is particularly significant when engineers raise the car and it doesn’t work in its operating window anymore. 

Hamilton indirectly explained it during post race interviews on Sunday, when he revealed to Sky Sports F1 that they didn’t change the heights of the car, but made other changes that affected performance: “But who said we raised the car? That's not true, we didn't raise it, we made other changes, but we didn't touch the height” 

The ‘changes’ refer to the fact that Ferrari shifted the balance towards the front end of the car to better manage the tyres during the race, in order to avoid graining, which showed off during the Sprint. 

This shift compromised Hamilton’s race, as the British driver struggled all the race long with the balance of his SF-25: with high fuel load the car was having understeer due to the high weight of the car, while as the car got lighter it became oversteery, due to the setup chosen by the engineers to prevent front tyre degradation.

Hamilton’s disqualification is proof that the car has been kept very low for the whole weekend to have a higher level of downforce generated by the floor, which led to an excessive plank wear and eventual disqualification.

According to the Article 3.5.9 of the FIA technical regulation: “The thickness of the plank assembly measured normal to the lower surface must be10mm ‡ 0.2mm and must be uniform when new. A minimum thickness of 9mm will be accepted due to wear, and conformity to this provision will be checked at the peripheries of the designated holes.”

The hole at the rear of the car when this measure is taken at the end of every race is the one highlighted by the red arrow in the drawing below and the disqualification of the 7-time world champion meant that the wear of the skid block was higher than permitted on his car. 

On the other hand, Leclerc was more competitive during the race: thanks to the broken front wing endplate in the first lap, the Monegasque driver lost around 25-30 points of downforce on the front axle, which actually made the car more balanced: the usual strong front end became quite weak due to the damage, thus matching the downforce generated on the rear axle and making his SF-25 much more balanced and quick, especially on the medium tyre. 

Leclerc himself felt very confident, saying after the race that the pace of the ‘broken’ car was actually very good: “All in all I think we had a really good race car. So I do not expect the car to be faster like that. So otherwise we have a problem.  I honestly think today we had a place to fight with the guys in front and when I mean the front I mean the McLaren.”

His words were probably a bit too optimistic, but are the proof of how much more balanced the car was even with less downforce. It’s however not given that with the normal wing he would have seriously had McLaren’s pace. 

In conclusion, the two problems mentioned above have been the hidden cause behind the negative wane of performance between Friday and Saturday in both China and Australia: in Melbourne, after showing off an extremely competitive pace on Friday, the team had to raise the SF-25 after free practices to avoid an excessive plank wear during the wet race, consequently losing tons of performance from the diffuser during qualifying and race. In China the scenario was quite different, but denounced the same two problems in a very evident way. 

The goal for the team should be to try to understand whether these problems can be solved with a series of upgrades or if it’s better for them to spend economic resources and wind tunnel hours to the 2026 project.