Technical analysis of the BMW F1.09

BMW Sauber had the only full interim car running with semi-legal bodywork, slicks and KERS before Christmas, so the unveiling of the F1.09 at Valencia's Ricardo Tormo circuit didn't produce any major surprises.

With the greater resources applied to it since mid-2008, the F1.09 appears to be more complex and considered than any of its rivals. Additionally, despite a conservative commitment to have KERS ready for Melbourne, BMW are believed to be ahead of their rivals in hybrid development.

The huge front wing is unchanged from the test car, with a simple main plane and a two element flap. As with McLaren only the top flap moves, controlled by an electric motor fitted inside the endplate. Also carried over from the test car are the ungainly endplates and the nose cone, which still has the turning vanes affixed to its lower edge but has gained some shaping to its vertical sides.

Sat behind the nose cone is a new front suspension. Technical director Walter Riedl explained that the car needed different suspension to suit the new slick tyres and this was largely the reasoning behind running the two interim cars in winter testing. While he emphasised the changes made to the rear suspension, the front is also different with the wishbones and steering arms now shaped to maximise their aero effect with the simpler front wing.

One change has been to raise the rear leg of the upper wishbone; this will alter the car's anti-dive properties under braking, but is most likely to be an aerodynamically-driven change.

What differentiates the F1.09 from its rivals is the treatment to the front of the sidepods. The chassis blends into the front of the sidepods with a wedge shaped structure. This also forms the inner face of the sidepod inlet, while the areas just above and below it are aimed at influencing airflow over, and particularly under, the sidepod.

Without the 2008-style bargeboards (although a pair of smaller 2009-spec ones will be fitted to the car), the aerodynamicists are struggling to get the correct pressure and distribution of the flow passing under the car. BMW Sauber have come up with a very different concept with these wedge panels to partly solve the problem. The front edges of the floor and the edges of the splitter all feature jagged fins to send vortices to aid flow towards the diffuser. These wedges will probably also serve to cool the KERS batteries and control unit as there are blanking panels fitted to them.

The sidepods themselves are quite tall and broad, with little undercut, and almost as wide as the floor at their widest point. They then tuck in quite neatly at the rear with a moderate bulge to allow cooling air to exit. This is aided by a heavily-slotted section low down by the floor - these exits are legal because the sidepod bodywork 100mm from the ground is excluded from the tight regulations to the upper bodywork.

As with a lot of the bodywork on the launch car, the top body is largely the same as the test car, while the rear wing is the first definitive and legal two-element 2009-spec we have seen from BMW as the interim car ran a three-element narrow rear wing. At the rear of the car, the diffuser is a simple arrangement with the stepped section of the under body blending up into a V and raising up to merge with the rear crash structure.

As already mentioned, the car sports new rear suspension geometry. This required a new gearbox casting, still made by BMW in titanium. The gear cluster is not different in concept but has had attention to reflect the different loading it will receive from the KERS system charging and discharging. The KERS system itself is a BMW-developed electric solution with the batteries mounted in both sidepods and the control unit in the right-hand sidepod.

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