Tech Analysis | Ferrari's balance compromised due to new front suspension?

Revolution on the front suspension 

Since the first renders of the car started to spread online, it was immediately possible to see that Ferrari radically changed their car to extract even more performance. For this season, in fact, the Maranello based team decided to switch from a push-rod front suspension (where the rocker works by compression), to a pull-rod front suspension (where the rocker works by traction). 

The adoption of this new scheme has one main reason: it should allow, according to Ferrari’s engineers, to open new development paths and help extract much more performance. To understand the nature of this change, it’s important to analyse why a front pull-rod suspension has been largely adopted during the ground-effect era: 

- The first reason is related to the mass distribution, particularly important in an F1 car: in the pull-rod scheme, in fact, the suspension box is placed in the lower portion of the chassis, i.e., closer to the ground, which has a very positive effect for the centre of gravity; 
- Secondly, this scheme improves the stability of the aerodynamic platform, allowing the car to run very close to the ground without having porpoising issues. The fact that the car can run at very low ride heights increases the amount of downforce produced by the Venturi channels, improving the car’s stability and performance in medium and high-speed corners, exactly where Ferrari struggled the most last season; 
- Last but not least, this new design also hides some aerodynamic purposes: as underlined in the drawing below by the two yellow arrows, by connecting the pull rod to the chassis at its lowest point, it’s possible to free up a lot of space between the two wishbone and have a ‘cleaner’ flow directed towards the cooling inlet and bodywork of the car. 

All these aspects should not only improve the interaction between the suspension and the tyres, but should also help engineers find the right “temperature window” for the tyres, allowing the SF-25 to better manage them especially in qualifying, where the SF-24 struggled the most. 

The grip and the stiffness of a tyre, in fact, strictly depend on the tyre temperature and can highly change if this parameter is high or low: if the temperature is too cold, the tyre becomes very stiff and behaves as if it was a piece of wood, while if it’s too hot the rubber could melt and the deg would increase as a consequence. Having a look at the graph below, it’s possible to appreciate the relationship between tyre temperature (on the x axis) and tyre grip (on the y axis).  

Highlighted in yellow on the purple graph is the "optimal grip window” i.e. the optimal grip that a tyre can offer in a specific temperature range. The goal for engineers is always to find out when these conditions are achieved to have maximum performance. The challenge for teams, however, is to ensure that all the parameters, on which the behaviour of the tyre depends, align so that the tyre enters this “window" in which it offers maximum grip and the best performance.

Despite all these great advantages, the pull rod front suspension also has ONE big disadvantage: it takes time to fine-tune it. This learning period is something that also other teams experienced with this suspension scheme, like McLaren or Sauber.

Leclerc himself underlined Ferrari’s balance issues during the last day of testing: “We see the numbers we expected, even if yesterday afternoon and today we had a little more difficulty in managing the balance, so there is still a bit to do,” Leclerc told Sky Italia. “At the moment we are working hard to try to improve the balance, we struggled a bit in the last two days. We will see in Melbourne. But let’s say that in the last two days we struggled a bit more with the balance, so that’s where we are focusing more”.

This balance issue is caused by a very strong front-end that is matched with quite a weak rear. As it was possible to appreciate during testing, in fact, the SF-25 mainly struggled out of slow harpins and of medium-speed corners like 13 and 14, where traction was needed. 

However, having a weak rear end is much more solvable than a weak front end. The weak front-end issue is something that teams usually carry forward through the season and is strictly connected to the front suspension design (like Aston Martin last season). On the other hand, Ferrari managed to find more grip on the front axle also thanks to the new pull-rod suspension, but still needs to counterbalance the grip on the rear, usually done by setting different rear suspension parameters, differential settings or by adopting a different rear wing. 

Having a look at the drawing below, in fact, Ferrari didn’t adopt the best rear wing for the Bahrain International Circuit: the version chosen was a medium downforce one, characterised by a mainplane with a spoon in the central portion (pink arrow) that generates downforce in that area, while the rest of the airflow is quite unloaded to have a higher top speed. This spec should be perfect for a circuit like Albert Park, where a very good top speed is needed. 

Innovative solution on the diffuser ramp

Another very interesting section of the new SF-25 was the sidepod and diffuser ramp design: as visible in the drawing below, the sidepod is much bulkier than the version used last year and is characterised by a different cooling inlet, shaped like a "P". As for the lower edge (green line and arrow), it is much shorter and positioned higher than the 2024, proof that the team managed to obtain a larger undercut, feeding the channel directed towards the diffuser and beam wing. As for its upper portion, it also has a different shape, with a much more direct trend towards the rear, as highlighted by the yellow line and arrow. This design has as its main goal to create two different channels (one in the upper part and one in the lower part of the sidepod) that feed the diffuser and the beam wing, increasing the level of downforce generated by the bodywork itself.

Furthermore, the floor also shows a completely new design: the "G-line" i.e. the line that outlines the attachment of the floor to the chassis, is much more curvilinear and marked compared to the 2024. The floor edge wing has a greater height in the lateral portion (white arrow). Last but not least, a conspicuous "bulge" appeared on the diffuser ramp (purple arrow) which has the main objective of generating vortices avoiding the fluid separation. 

As visible in the explanation below, in fact, if we consider the cross-section of a diffuser with no bulge, it’s possible to appreciate how the flow detaches from the surface as it gets closer to the exit. On the  other hand, in the cross-section of the diffuser with the bugle it’s visible how the flow remains attached along the surface thanks to this cavity, that generates a vortex that avoids flow separation. This second design inevitably allows to generate more downforce from the diffuser, as when air detaches from a surface a stall occurs and that downforce is ‘lost’. 

In conclusion, the three days of testing in Bahrain were bittersweet for Ferrari, as they faced some tuning problems with their new front suspension. Despite this little inconvenient, the potential always seemed there and even if they could struggle a bit in the first couple races of the season, once they find the clue to the problem, they could challenge McLaren for important positions.