Subaru Impreza WRC03 aero and rally performance

Only nine months after the introduction of the Subaru Impreza WRC01 into the World Rally Championship, Subaru and Prodrive decided to start working on a new evolution of the car, based on the lessons learned in the rally stages and the deficiencies detected in the New Age Impreza. The goal was to develop a road car with the specific aim of giving the best possible platform for a rally-winning machine, which had to be more aggressive, more aerodynamic and with an improved cooling system. Also, weight reduction and a lower center of gravity were requested.

To better achieve these goals, both Subaru and Prodrive significantly increased their resources into the project with respect to previous versions: Subaru’s parent company, Fuji Heavy Industries and the company’s high-performance arm, Subaru Tecnica International (STI) established a 10-strong engineering team in Japan to lend support to the rally effort, while the engineering team based at the 555 Subaru Team’s UK headquarters in Banbury grew up by 30 percent. The design process represented a step ahead in the collaboration between both entities: it was a new integrated design process between Prodrive in the UK and Subaru in Japan, using common design and manufacturing systems to harness the engineering skills of both organizations. In addition, the Japanese team ensured access to a wind tunnel, test track and state-of-the-art technology.

P.Solberg/P.Mills, Subaru Impreza S9 WRC03, Rally Deutschland 2003, 8th. – Pîcture by Subaru World Rally Team

Kazuo Ogawa, who had been named Impreza chief in the spring of 2001, was responsible for the design of the new car in Subaru, while again Peter Stevens, on behalf of Prodrive, played an important role in the external and aero design.

The new car, that would become the fourth generation of the Impreza, included revisions to the engine, roll-cage, body panels and the aerodynamic package. A lighter and stiffer bodyshell was designed, while under the bonnet the turbo, exhaust manifold and engine mapping were modified to improve performance and power.

But one of the areas where more efforts were devoted was the improvement of the aerodynamic package. The main goals were to increase downforce generation without increasing drag and to improve the engine cooling efficiency.

One of the main solutions adopted to generate additional downforce was the introduction of a new rear wing, taller than the previous one, and with four vertical fins.

Subaru Impreza S9 WRC03 rear wing – Picture by Subaru World Rally Team

The addition of vertical fins allowed increasing downforce when the car was sideways, by using pressure from air flowing laterally, but it also increased drag. The Impreza WRC03 was the first WRC car to include them, and soon Peugeot and Ford reproduced the solution in their own rear wings. The solution quickly proved to be effective, as Petter Solberg recognized in this interview for Rallirinki published inside the #ReliveRallyFinland2003 project: “In Finland, they helped a lot in the high-speed corners. I think it was 0,1-0,2 seconds per kilometer in the speed on the corners”.

To compensate the increase in drag caused by the new aero package, the car front was re-styled to a more rounded (aerodynamic) design (which reduced the drag coefficient Cx) and with a smaller frontal area (which also reduced drag resistance). Although, at first sight, the design of the side mirrors seemed to be more aerodynamic in the WRC01.

Subaru Impreza WRC 01 (above) and WRC03 (below) – front bumper and bonnet comparative

The picture above shows the more rounded design (aerodynamic) and smaller frontal area of the WRC03 version. In replacement of the controversial head lamps from WRC01 car, the new headlamps were more integrated into the front bumper/bonnet system. The shape of the new head lamps made this version of the Impreza to be known since then as blob eye (in opposition to bug eye for the 2001 version, or hawk eye for the 2006 version).

The size of the air intakes in the front bumper was increased with respect to the previous version, which contributed to a better engine cooling.

P.Solberg/P.Mills, Subaru Impreza S9 WRC03, Rally Australia 2003, 1st – Pîcture by Subaru World Rally Team

Also, the increase in size of the bonnet (intercooler) air intake, combined with some internal modifications, such as the shape of the intercooler water spray nozzle and the air baffle plate inside the air scoop, contributed to the improve the engine cooling efficiency.

The first prototype car of the Impreza WRC03 (which would be officially labeled as S9) was unveiled in Paris Motorshow, in September 2002. Only a few days later, the development tests started in Spain and Andorra. First was Paolo Andreucci to develop the car on some asphalt roads near Vic, and then Pasi Hagström spent three days working on gravel routes in Northern Catalonia and Andorra. At the same time, Tommi Mäkinen was carrying out some development tests of the road car in the German circuit of Nurburgring.

The development tests continued during the next weeks. In December, tests were developed in the French Alps, this time with Tommi and Petter, to continue the car development work while preparing Rallye Monte Carlo.

For 2003 the Subaru Team benefited from the continued backing of International cigarette brand 555 and an exclusive arrangement with Pirelli for tire supply, which would reveal key in the future success of the new car. The human team remained from previous seasons, with Petter Solberg/Phil Mills and Tommi Mäkinen/Kaj Lindström as official drivers, led by David Lapworth (Team Principal), George Donaldson (Sporting Director) and Paul Howarth (Team Manager). Main team additions were Steve Farrell as Chief Engineer, Pierre Genon as Chief Rally Engineer and Michael Zotos as Mäkinen engineer.

P.Solberg/P.Mills, Subaru Impreza S9 WRC03, Rallye Monte Carlo 2003, retired- Pîcture by

In the season opener, Solberg and Mills confirmed the potential of the car by setting the second-best time in three of the four initial stages. Unfortunately, they had to retire in the longest stage (47km) SS5 – Plan de Vitrolles 1 due to an accident under damp conditions, while some minutes later it was the car of Mäkinen and Lindström who was forced to abandon after another accident in an icy section of the same stage.

T.Mäkinen/T.Rautiainen, Subaru Impreza S9 WRC03, Rally Sweden 2003, 2nd – Pîcture by Subaru World Rally Team – eWRC.cz

The expected result arrived in Sweden, after a fruitful pre-event test near Torsby. There, Mäkinen/Lindström completed a very regular race, which positioned them in the second position since the third stage, a position they were able to defend to the finish line, giving the car his first podium position, as well as its first stage wins.

One of the keys of the future success of the car was the intense test development program the team undertook all over the season, with multiple tests sessions in Spain, France, Andorra and the United Kingdom. Tests were developed by test drivers Pasi Hagström and Paolo Andreucci, as well as by official drivers.

P.Solberg/P.Mills, Subaru Impreza S9 WRC03, Rally New Zealand 2003, 3rd – Pîcture by Subaru World Rally Team

The second podium for the new car arrived in New Zealand, where Solberg/Mills reached the third position after the second stage, and after a very regular event were able to keep that podium position, with Mäkinen/Lindström finishing in the seventh position.

P.Solberg/P.Mills, Subaru Impreza S9 WRC03, Rally Acropolis 2003, 3rd – Pîcture by Leszek Kusmirek – eWRC.cz

Things improved gradually in the next three events (Argentina, Greece and Cyprus), all under very rough conditions, proving that the gravel test development work had paid off. The duo Solberg/Mills was fifth in Argentina and reached another podium in Greece, where they finished in the third position.

Under the hot conditions of these events, the team introduced a roof scoop, in order to allow fresh air entering into the car and reducing inside temperature. It was only used in Argentina, Greece and Cyprus, but surprisingly not in Turkey.

P.Solberg/P.Mills, Subaru Impreza S9 WRC03, Rally Cyprus 2003, 1st – Pîcture by Subaru World Rally Team

Rally Cyprus represented a big step ahead for the team. After a rough battle with the Peugeot 206 WRC of Grönholm/Rautiainen and Rovanperä/Pîetiläinen, Solberg/Mills were third at the end of the first leg. But a superb charge on the second day catapulted them to the leadership, which they maintained right to the end of the event, giving the car its first win in the WRC Championship. Mäkinen/Lindström were also in the battle until stage 6, where they dropped 28 minutes due to a rear-wheel broken, 3km in. The Finn duo stopped to remove the rear corner upright, damper and rim on the roadside, before rebuilding it and putting on a new wheel in the searing Cypriot heat and with limited tools. They showed very good repair abilities, as they were able to set the fastest time in the next stage…before being disqualified due to a penalty for the excessive time lost between stages.

The Impreza WRC03 showed again a very good pace in the Finnish gravel, in what was its 10 anniversary: the first version of the Impreza had made its WRC debut in 1993 in the Rally of Finland.

P.Solberg/P.Mills, Subaru Impreza S9 WRC03, Rally Finland 2003, 2nd – Pîcture by Subaru World Rally Team

Solberg/Mills reached a brilliant final second position in Finland, once Grönholm/Rautiainen had to withdraw after their epic battle with Markko Martin and Michael Park we already reviewed in our post on Rally Finland 2003, generated inside the Rallirinki’s #ReliveRallyFinland2003 project.

P.Solberg/P.Mills, Subaru Impreza S9 WRC03, Rally Australia 2003, 1st – Pîcture by Subaru World Rally Team

The good pace even improved in Australia, where Solberg/Mills were able to fight for the lead with Grönholm/Rautiainen and Loeb/Elena. After the retirement of the Finnish duo, the fight with the Citroën lasted until the end, with constant leader changes. Only in the penultimate stage (SS23 Bannister West), Solberg and Mills were able to obtain an 8 seconds margin over Loeb/Elena (their biggest difference in two days) that allowed them to ensure the rally win at the end. The ten points obtained repositioned them into the fight for the Championship, after a deceiving start of the season. But the next three events were to be run on tarmac, a surface where the Impreza WRC03 had not performed especially well until then.

P.Solberg/P.Mills, Subaru Impreza S9 WRC03, Tour de Corse 2003, 1st – Pîcture by Subaru World Rally Team

Rally Sanremo confirmed such a negative trend, as none of the Imprezas WRC03 were able to follow the battle between Citroën, Peugeot and Ford for the top positions. Solberg/Mills had to retire in SS7 when they run out of fuel, while Mäkinen/Lindström were only 10th. And things did not improve in the next event when Solberg/Mills destroyed their car in the shakedown. Mäkinen offered his car to Solberg so he could still fight for the Championship but, after working 16h in the night, the team was able to repair Solberg/Mills’ car and the car reached the start line of SS1 on due time. Such an impressive team effort was recognized by FIA, as the crew was awarded the Inmarsat Star of the Rally by a panel of FIA WRC experts.

At the end of the first leg, Solberg and Mills were in 8th position, 44 seconds behind leading duo Loeb/Elena. But in the second day, only six stages later, and after an impressive performance by Solberg and Mills, the Impreza WRC03 had reached the leadership of the event. And they were able to increase their margin over Duval and Sainz, to reach the first win on tarmac of the car.

T.Mäkinen/T.Rautiainen, Subaru Impreza S9 WRC03, Rally Catalunya 2003, 8th

The fourth position obtained by Solberg/Mills in Rally Catalunya, combined with the results of the other title contenders, left one of the tightest Championship classifications before the final event. Sainz and Loeb shared the lead, with Solberg one point behind, and Burns with a five points disadvantage with the leading duo. Unfortunately, the British driver had to renounce to participate in Rally Wales GB, due to a physical problem that became a fatal illness months later. But for the remaining trio in contention, only the win ensured the title, so a fierce battle was expected.

P.Solberg/P.Mills, Subaru Impreza S9 WRC03, Wales Rally GB 2003, 1st – Pîcture by Subaru World Rally Team

Sainz and Martí soon lost their chances, as they had to retire after an accident in SS3, due to a loss of concentration caused by a previous incident with the onboard camera (which caught fire). Loeb and Elena did a great start, by setting the fastest time in SS2 and SS3, but the team orders to ensure the necessary points for the Manufacturers Title as well as the reply from Solberg/Mills, who started a series of fastest times, allowed the Subaru duo to reach the leadership. And they were able to slowly increase their advantage over the Citroën. However, at SS14, all could have changed: Solberg/Mills hit a pothole and damaged the Subaru’s steering. Even so, they managed to win the stage and to continue to dominate the timesheets until the last stage, winning the rally by a margin of 44 seconds. Only one year after their first win in the Championship, Petter Solberg and Phil Mills became World Champion, while Citroën ensured the Manufacturer’s crown.

T.Mäkinen/T.Rautiainen, Subaru Impreza S9 WRC03, Wales Rally GB 2003, 3rd – Pîcture by Subaru World Rally Team

Wales Rally GB 2003 was also the last race of Tommi Mäkinen and Kaj Lindström in the Championship. Several months before, the brilliant Finnish driver had announced his intention of retirement at the end of the season. To commemorate it, the team replaced the usual Subaru sticker in his car bonnet by a sticker with his name and the sentence World Rally Legend. And their final race couldn’t have gone better, as they finished third right behind the duo fighting for the driver’s title, and in a close fight with Colin Mcrae and Derek Ringer, also in their last official outing. It was a very happy day for the team and the winners, but also a sad day for the rally community, due to Burns absence as well as the announced retirement of former World Champions Tommi Mäkinen and Colin Mcrae (although the Scottish would come back for some events in 2005 and 2006). The season 2003, and more specifically the Wales Rally GB 2003 represented the transition to the next generation of drivers, which included Petter Solberg, Markko Märtin or Mikko Hirvonen, but that would certainly be dominated by two names, Sebastien Loeb and Daniel Elena.

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