Were the results measured? (It looks like increased drag and rear lift to me (from the shape of the top side, don't know if the secret diffuser is doing anything))
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2016: 128.75L for 1875.00km => 6.87L/100km (34.3MPG US)
2017: 209.14L for 4244.00km => 4.93L/100km (47.7MPG US)