here's some more info about the Eco model:
"Cruze Eco Details
The Eco achieves greater fuel economy using a number of features that enhance its aerodynamics, minimize weight and reduce rolling resistance. Details include:
* A lower front grille air shutter that closes at higher speeds to improve aerodynamics and opens at lower speeds to optimize engine-cooling airflow;
* The upper grille has more "closeouts" to improve aerodynamics;
* A lower front air dam extension, extensive use of underbody panels and a rear spoiler enhance aerodynamics;
* A lowered ride height (11 mm) improves aerodynamics;
* Unique 17-inch lightweight aluminum wheels;
* Ultra-low rolling resistance 17-inch Goodyear tires.
* The axle ratio on the manual-transmission model is also optimized for fuel economy, while helping the car deliver confident performance.
Chevrolet estimates the Cruze Eco will deliver 0-60 mph performance of about 10 seconds with the manual transmission and 9 seconds with the six-speed automatic."
"Chevy Unveils 2011 Cruze Eco; Turbo Compact Gets an Estimated 40 MPG Highway" Green Car Advisor