Literally, every square milimeter counts
The new BMW M4 DTM spent 50 days in the wind tunnel. Test sessions could last up to 15 hours. But not a minute more.
BMW assembles the new M4 DTM entirely by hand. This means that the development team must rely on accurate measurements one every piece is glued to the other for two reasons: regulations and aerodynamics.
While DTM rules allow no leeway or interpretations, it's a car's aero signature that needs extensive adjustments months before the racer runs its first shakedown laps.
Over the years, BMW's aero testing procedure evolved. Nowadays, a session in the wind tunnel is similar to a test day on the track. Modularity also plays its part – BMW says that the new M4 DTM is assembled in such a way that the body kit allows quick aero mods.
The M4 DTM's hood, for example, is made of eight pieces that can be independently changed, which allows BMW's aero experts to test up to three car configurations per hour.
Subsequently, every tenth of a millimeter counts in the wind tunnel. That's when the double-robot-arm measurement cell comes into play.
With a measurement accuracy of under 100 micrometers (the average thickness of one human hair), two pairs of sensors feed info into a computer which creates a 3D image of the entire car. It's the same system used for the new BMW 5 Series.
The rendering is then compared to the original design plans as engineers hunt for any discrepancies that need fixing.