Rally1 aero developments for 2025

The lack of end-of-season test days in the last seasons has forced Rally1 teams to use the pre-event test sessions of the second half of the season to test the new developments for the next season. And it has been the same again in 2024.  After the Central European Rally, by our count, both Toyota and Hyundai have used the 21 test days available for the year (while M-Sport still has 3 available) which means that both teams can only test in their home test area till December… if the Finnish weather allows. Or, to take part in national/regional events. Thus, it is a good moment to compile the modifications we have seen in the recent tests.

The cooling of the hybrid system continues to be the main focus of the Rally1 teams’ innovations. Once it became clear that the cooling requirements were lower than expected, the teams set about introducing modifications to minimise the impact of the measures introduced in 2022 to ensure proper cooling. If in 2023 it was Toyota who removed the side air intakes, it was only a matter of time before M-Sport did the same with the Ford Puma Rally1, the car with the most prominent intakes at present. And the modification already appeared in the pre-event test for the Rally Acropolis.

A.Fourmaux/A.Coria, Ford Puma Rally1, 2024 Rally Acropolis pre-event test –  image extracted from this video by SUDrallye

The original air intakes have been cut back, significantly reducing the frontal area, as shown in the image below, while the size of the air intake has been enlarged towards the rear to ensure adequate airflow to cool the hybrid system. Such a modification was also test in the Central European rally PET, by Munster/Loukka.

A.Fourmaux/A.Coria, Ford Puma Rally1, 2024 Rally Acropolis pre-event test showing the car with the original (left) and the new (right) side scoops –  both images extracted from this video by SUDrallye

The benefits of the modification, should the tests confirm that the cooling capacity is not affected, are reduced drag and increased downforce. Drag is reduced due to the reduction in the frontal area of the car, as well as by the reduction in the drag coefficient, as the shape of the car in that area becomes smoother (more aerodynamic). And more downforce is achieved by the rear wing, as the airflow reaching that element is now cleaner, making the wing more efficient.

Detail of the new side scoop recently tested on the Ford Puma Rally1

The low cooling demand of the hybrid system is also behind the modification introduced by Toyota on the GR Yaris Rally1 during the last pre-event test sessions, for Chile (in Finland) and CER (in Austria). Possibly favored by the low ambient temperatures in these countries at this time of the year, the car was seen without any fan attached to the radiators visible through the rear bumper.

The original design of the car included two fans to force air coming from the side ears to flow across the rear radiators, to cool down the hybrid unit and batteries. During 2023, the team tested (and finally implemented) the removal of one of the fans. Removing the second was also tested, but discarded as considered too risky, as Tom Fowler explained to us during the 2023 Central European Rally (here).

Toyota GR Yaris Rally1 in Rally Sardegna 2022 (left) and 2024 (right) showing two fans in 2022 and only one in 2024 – images by Toyota Gazoo World Rally Team

The decision seems to have been reconsidered in the last months, and the remaining fan has also been removed in the recent tests, to evaluate the impact on the cooling capacity. If results are satisfactory, we might probably see this solution applied in most of the events in 2025, except maybe in those with higher ambient temperatures.

S.Ogier/V.Landais, Toyota GR Yaris Rally1, 2024 Central European rally pre-event test – image extracted from this video by Karel Štěpán

The benefit of such modification is to remove extra weight in the overhangs of the car, thus improving the car handling. But this solution has also downsides: the energy of the air leaving the fans was used to help remove air from the rear wheel spaces (expelled through the side exits)  as well as to remove air from under the car (partially reproducing the exhaust-blown effect seen in the WRC+ cars). Without any fan, less air can be extracted from these two areas, leading to higher pressure under the car, that is, reducing generated downforce, thus less rear grip.

No aero-related modification has been observed in the Hyundai i20 N Rally1 in the last months, as the team has concentrated on the modifications to be introduced in 2025 to the chassis. To do that, the team was allowed to use 4 jokers (2 from 2025 and 2 from 2026), as compensation for the (canceled) new car planned to be introduced in 2025 but finally discarded after the announcement early this year of the new regulations by FIA that made Hyundai paralyse the design work. Most of the modifications will affect the suspension, where a change in the angle of the shock absorbers is expected. Images seen from different tests would confirm that the team is already testing new designs on this side.

E.Lappi/J.Ferm, Hyundai i20 N Rally1, 2024 Rally Finland pre-event test – image by Henri Vuorinen Photography

Due to the magnitude of the modifications to be made in the chassis, it is likely that the team will use up all 4 available jokers, and other modifications, including those related to the car’s aerodynamics, shall not be introduced. Among them is a (slight) modification to the rear wing.

Hard times ahead for engineers to develop and test the new modifications with so many test limitations, and a lot of paperwork to get them homologated. Next January we will know how many of them are finally introduced.

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