Why do I get better mileage when driving slowly?
Keep your speed and MPG in check to be a greener driver.
Wed, Sep 17, 2008 at 02:32 PM
Q. I know that driving more slowly is one of the main things you can do to save gas and lower emissions from your car, but why is that, exactly?
– Jake, MT
A. This sounded like a question for Expert Champion Hypermiler Wayne Gerdes. He’s that dude you may have read about in the news, who gets five billion miles (hardly an exaggeration) to the gallon in his plain old Honda Accord. So that’s exactly who we asked. Here’s what Wayne has to say about why it pays to resist putting the pedal to the metal:
"Above 50 miles per hour, aerodynamic drag overcomes the tire rolling resistance mechanical drag. The engine mechanical drag is somewhere in the middle, but it increases as speed increases with RPM. Above 50, aerodynamic drag begins to overwhelm all other drag, or energy losses in the vehicle. This is not specific to any vehicle, I’m giving you an average. Right around 50 mpg is where things go south. Above 55 miles per gallon you really begin to get burned."
This from a man who (no exaggerating now) gets 50-55mpg in his 2005 Honda Accord in summer, and 40-45 mpg in the winter. That’s twice what the EPA estimates he should be able to get in a 2005 Honda Accord, so you know you better listen up.
Now try this at home, kids: Gerdes suggests you shell out $150 for a fuel consumption display (if your car doesn’t already have one built in), take her out on a flat highway some day when it’s not particularly windy, and get a sense of where that fuel economy point maxes out. Once you find your sweet spot, stay there. Whenever possible. If your car’s sweet spot is 40mpg, roll with it. Don’t go so slowly that you’re a safety hazard on the highway, of course, but also don’t forget to enjoy how incredibly annoying you are to the other gas-guzzling cars on the road. And how much money you’re saving! Gerdes says you’ll earn back your $150 in just three to four months of driving at your vehicle’s sweet spot speed. Go on—drive like grandma.
Story by Tobin Hack. This article originally appeared in Plenty in September 2008. The story was added to MNN.com in August 2009.
Copyright Environ Press 2008
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