The history of the 2006 Subaru Impreza WRC car began the day after the WRC 2005 was introduced, at Rally México 2005. Subaru was ready to launch a new version of the Impreza road car, while the FIA was preparing the biggest shake-up of the technical rules since the WRC formula had been introduced in 1997.
The Impreza 2006 road car was designed in Japan by the FHI (Fuji Heavy Industries) design team, led by Andreas Zapatinas. Its new body shape provided some significant aerodynamic advantages, with improved airflow around the front and the sides of the car, and a new headlight design that resembled the face of a hawk, for what this version of the Impreza was soon known Hawkeye.
P.Solberg/P.Mills, Subaru Impreza S12 WRC’06, 2006 Rallye Monte-Carlo, retired – image by Subaru World Rally team7th
For the 2006 WRC season, cutting costs was, as ever, one of the FIA’s main concerns. The solution it adopted was to ban active differentials and water injection. Teams were also obliged to re-use cars and engines across selected pairs of events – a system first tried on some rallies in 2005, an that has survived to this day.
With all these facts in mind, Prodrive engineers at Banbury, led by Director of Engineering Steve Farrell, began work on the new WRC car, with manufacturer principal Shigeo Sugaya supervising the collaboration with the Japanese design team. The restyled exterior offered an opportunity to reduce drag, with concave horizontal corner spoilers on the front bumper smoothing the airflow down the sides of the car.
P.Solberg/P.Mills, Subaru Impreza S12 WRC’06, 2006 Rally Catalunya, 7th
A key new feature was the spread-wings mesh front grille, with a centre section resembling an aeroplane fuselage and sweeping outer sections mimicking wings. Fuji Heavy Industries Ltd, Subaru’s owner, has its origins as an aircraft maker. Only the right-hand side was open (A), providing an air feed to the engine, while the central and left-hand sides were blocked.
The front bumper included a large central air intake (B), a small intake for front brakes cooling (C) on the left-hand side and a prominent front splitter (D).
Subaru Impreza S12 WRC’06 engine
The intercooler was placed horizontally behind the front grille and above the radiator. Cooling air entered through the lower intake and, after passing through the vertical radiators and the horizontal intercooler, was expelled through the central bonnet vent by means of a fan, as shown in the images. The bonnet vent included deflectors to force hot air towards the windscreen, bypassing the blocked intercooler intake.
Subaru Impreza S12 WRC’06 bonnet vent
Excess air from the engine bay was removed through openings at both ends of the bumper (E), acting as air curtains, to reduce drag around the front wheels, a solution still used today in cars like the Škoda Fabia RS Rally2.
P.Solberg/P.Mills, Subaru Impreza S12 WRC’06, 2006 Rally Catalunya, 7th
The new side-skirt design contributed to the car’s sporting stance, integrating better with the overall body design and featuring sweeping swage lines that continued into the rear bumper. As usual, the goal was to prevent air from entering beneath the car, thus maintaining low pressure and improving grip.
Rear wing of the Subaru Impreza S10 WRC’04 (top) and S12 WRC’06 (bottom) – images by Subaru World Rally team (top) and llluis555 (bottom)
At the rear, the massive rear wing already used on the 2004/05 car was retained, but its efficiency was significantly improved with the addition of the roof vane, an aero lip running along the rear of the roof and covering the top half of the rear window.
Subaru Impreza S12 WRC’06 roof vane
Fuji Heavy Industries’ aerodynamics department developed the roof vane with the intention of fitting it to both the road car and the WRC car. The presence of the large rear wing made it even more effective on the WRC car.
Subaru Impreza S12 WRC’06 rear aero package
The aim of the roof vane was to capture the air flowing over the roof, which often become detached due to the generation of vortices at the rear of the roof, and forcing it to flow beneath the vane. The consequence was that more air flowed beneath the rear wing, where it was accelerated, thus reducing pressure beneath the wing. This increased the pressure difference between its two sides, resulting in more downforce.
Graphical representation of the impact of the roof vane on the air flowing over the roof of the car
In summary, the addition of the roof vane made the rear wing more effective at generating downforce and improving stability.
Rally cars with roof vane: Lancia Stratos (left) and Fiat 131 Abarth (right) – images by Stellantis
The roof vane became one of the most characteristic exterior features of this Impreza version, although it wasn’t new to rally cars. A similar solution had already been used in the early days of rally aerodynamics on iconic models such as the Lancia Stratos or the Fiat 131 Abarth, although at a more forward location, on top of the roof.
The effect of the small aero device made a big impression on Tommi Mäkinen or Stephan Sarrazin. The French driver had the opportunity to test it while driving the Impreza WRX that contested the legendary ’24 Hours of the Nürburgring’ touring car race in Germany in June 2005, with a prototype of the vane fitted to it.
K.Shimizu/K.Sato/T.Yoshida/S.Sarrazin, GDB-type Impreza WRX STI (E-type), 2005 Nürburgring 24-Hour Race, 2nd in class – image by Prova Racing Division
However, the 2006 car introduced more than just aerodynamic modifications. The engine had to be adapted to operate without water injection, but the team took advantage of this modification to improve the control, the fuel system, weight and friction, resulting in a more powerful, lighter and more responsive engine, with more torque.
The transmission also had to be redesigned to adapt to the mechanical differentials imposed by the new regulations. The six-speed transmission was further refined with a new hydraulic system that gave better control of the center differential and faster gear change.
Elsewhere in the car, from front to rear, other smaller revisions were made to areas including the wiring loom, fuel system, electrical systems and the location of systems in the cockpit. Safety was improved through the incorporation of stronger materials in high-stress areas of the roll cage, which was modified to accommodate a new, stronger type of seat for driver and co-driver as well as modifications to the passenger compartment, seat supports and seatbelts.
Total weight was also reduced through the use of thinner window glass, more aluminium panels and a thinner-gauge steel roof, while the center of gravity was lowered.
S.Sarrazin/S.Prévot, Subaru Impreza S12 WRC’06, 2006 Rallye Monte-Carlo, 5th – image by Subaru World Rally Team
All these rule changes meant that Subaru, along with every other team, was obliged to run its 2006 car from the first rally of the year, rather than introducing it in México, as had usually happened in previous years.
The Monte-Carlo debut was discreet: Solberg/Mills retired due to an early engine failure, while Sarrazin/Prévot finished fifth after posting some interesting stage times, including three second-fastest times. However, the roof vane attracted the attention of other teams. After the event, the issue was reported to the FIA Manufacturers’ Commission with regard to the technical regulations. The controversy arose from the fact that it was considered -through not clearly specified in the regulations- that elements providing an aerodynamic effect on the windscreen were forbidden. The Commission considered the question and eventually modified the regulations. Since then, it was clearly stated that “additional safety fastenings for the windscreen and the side windows may be fitted provided they do not improve the aerodynamic qualities of the car.” Subaru was at least allowed to use it throughout the lifetime of the WRC’06 version.
T.Arai/T.Sircombe, Subaru Impreza STI N12, 2007 Rally Acropolis, 1st Gr. N – image by Kostas Anagnostopoulos/eWRC
However, the new regulation did not apply to Group N cars, which were based on production cars. As the roof vane was present in the STI road car, the Impreza Gr. N was allowed to continue using it, much to the pleasure of drivers such ase Toshi Arai, who had previously confirmed the benefits of the rear vane: “Downforce at the rear dramatically improved with the group N machine since the roof vane was installed”.
P.Solberg/P.Mills, Subaru Impreza S12 WRC’06, 2006 Rally Sardegna, 9th – image by Subaru World Rally Team
The combination Impreza/Pirelli had always performed well in México, and the 2006 edition was no exception. The team faced the rough Mexican stages with two important novelties: the introduction of the roof scoop to improve cooling for the cockpit and drivers -something critical in México- and the arrival of François Xavier Demaison (ex-Citroën, ex-Peugeot) as Petter Solberg’s engineer. With all these changes, the Impreza driven by the Norwegian set the fastest time on the first four stages of the event and finish the first leg in the lead. They could not withsatnd the attack by Loeb/Elena during the second leg, but they finished in an excellent second position, the first podium of the new car.
P.Solberg/P.Mills, Subaru Impreza S12 WRC’06, 2006 Rally Catalunya, 7th
In 2006, the presence of the roof scoop was not compulsory, even after it had been used once. The team therefore removed it for the following events -Catalunya, Tour de Corse and Argentina- and only fitted it again for the hot summer events, from Sardegna on. It was again removed in Japan, Great Britain, Monte-Carlo’07 and Sweden’07.
The car proved well suited to rough terrain, with Solberg/Mills finishing second in Argentina and Australia, before closing the year with third place at the RAC Rally. Chris Atkinson and Glean Macneall achieved their best result in Japan, finishing fourth.
C.Atkinson/G.Macneall, Subaru Impreza S12 WRC’06, 2006 Rally Australia, 9th – author unknown
Results did not improve in the opening events of the 2007 season, still completed with the WRC’06 car. The fourth places of Sarrazin/Prévot in Monte-Carlo and Solberg/Mills in Norway were the best results. Then, in México, the team introduced a revised version of the car, named S12B WRC’07, without the controversial roof vane and with multiple changes affecting weight distribution, suspension geometry, differentials, new dampers and a different radiator and intercooler arrangement, combined with a new bonnet vent design.
P.Solberg/P.Mills, Subaru Impreza S12B WRC’07, 2007 Rally México, 2nd – image by Subaru World Rally Team
The 2007 car debuted in Rally México 2007 with a promising second position for Solberg/Mills. However, this proved to be the top result of the car, which would be remembered as the first Subaru rally car not to win a round of the WRC Championship, after so many successful years.
