Quote:
Originally Posted by Skyman 08
My HHR was rated at 28 mpg hwy, I get close to 32.
my Sky was rated 28 hwy I get about 27.
both have the same engine 2.4L 170 hp
HHR weighs more, HHR has a 4 speed automatic
Sky weighs less, Sky has 5 speed automatic...
I drive both the same on the highway. why the difference?
Gearing
HHR 2100 RPM @ 70 mph
Sky 2350 RPM @ 70 mph
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Highway mileage is all about gearing and drag (aerodynamic, tire rolling resistance, and drivetrain loss are the main sources of drag).
I'd assume the Sky has far less drag; it should have less frontal area AND lower drag coefficient. I can't even begin to guess at rolling resistance, which while it is a significant portion of fuel economy, is lacking in hard data -- nor do I know sizes, loads, and pressures of tires in either car. Drivetrain loss may be about even, except that the Sky seems to have a more modern transmission.
Still, all those advantages that the Sky has can't make up for that slight difference in gears.
This is why I keep posting my worry about the Camaro's 6 speed, wondering if the ratios will be too close and it will be at like 2500 or 3000 rpm at 70mph. There was a post with gear ratios and rear end ratios listed, but I can't find it anymore... anyway, four close-ratio gears are enough for the speed demons to get up to their speed, then the last two should be way far apart for economical drivers.