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Old 02-17-2012, 10:24 AM   #29 (permalink)
PaleMelanesian
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Join Date: Dec 2007
Location: Texas
Posts: 2,321

PaleCivic (retired) - '96 Honda Civic DX Sedan
90 day: 69.2 mpg (US)

PaleFit - '09 Honda Fit Sport
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90 day: 44.06 mpg (US)
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From what I've researched (no references right now, sorry), it's mainly air drag and tire friction. From 100F to freezing, air drag increases 10% and tire rolling resistance doubles. Using the calculator, for the average car that means ~30% lower mpg at 35 mph and ~20% lower at 70 mph. You can add on top of that any extra warmup, lube friction, lower tire pressure if you don't keep up with it, etc.
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11-mile commute: 100 mpg - - - Tank: 90.2 mpg / 1191 miles
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