BMW is expanding its eco-friendly 'efficient dynamics' to the Z4 roadster and coupe.Already used in the 1-series, 3-series and 5-series, 'efficient dynamics' aims to save fuel and reduce emissions without compromising agility.Whereas BMW's existing systems are predominantly focused around regenerative braking and combined alternator/starter motor units, the Z4 uses a new, more efficient rear axle transmission.This 'friction optimised' rear axle lowers CO2 outputs and increases economy for all six-cylinder Z4s except the Z4M. The 2.5si goes from a combined economy of 33.6mpg to 34.0, with CO2 output down from 202 to 199g/km. The 3.0si goes from 32.8 to 33.2mpg and 207 to 204g/km, and the 3.0si coupe from 31.7 to 32.5mpg and 213 to 207g/km.The 2.0-litre four-cylinder engine has also been made more efficient, with CO2 dropping from 181 to 176g/km and mpg rising from 37.7 to 38.2.The changes apply to all Z4s built from 1 September 2007. They're not huge changes, granted, but we reckon they're still significant.
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