Today: Frank shares the simple way he scored another 10 MPG out of his car.

Dear Car Talk

Dear Car Talk | Jul 01, 2007

Dear Tom and Ray:

I found the answer to getting better gas mileage. It's called SLOWING DOWN. Instead of the usual 75 mph on the highway that I've done for ages, I tried an experiment now that gas is three bucks a gallon. Today the wife and I drove from Memphis to Texarkana, which is 300 miles. I set the cruise control at 60 mph the whole way. Yes, I got passed by everyone and everything, but I got the last laugh when I pulled into the gas station and put 6.73 gallons in the tank, for a mpg rating of 44.5. And just so you don't think I was driving a little teapot, I was in my 2004 Chevy Malibu with a 3.5-liter V-6 engine and 76,000 miles on it. Today's mileage was 10 mpg better than I've ever gotten in this car. So this is how we can kick our oil habit, or at least reduce our thirst, as a nation. Your thoughts? -- Frank

TOM: You're absolutely right, Frank. There's no doubt about it: Slowing down increases gas mileage.

RAY: Since you've done this experiment only once, we can't vouch for your actual mpg numbers. You'd have to do it a few times to determine whether the numbers are accurate. But the scientific data certainly backs up your theory.

TOM: You might recall that in the 1970s, the Nixon administration imposed a nationwide 55-mph speed limit. Why? Because they knew that if everybody drove at 55 mph instead of 75 mph, the country would save a buttload of fuel!

RAY: The reason that slowing down works has to do with wind resistance. You might think, "Well, how much more wind resistance is there at 75 mph compared with 55 mph?" And the answer is: a lot.

TOM: Wind resistance increases by the square of your speed. If you square 55 (55 x 55), you get 3,025. If you square 75 (75 x 75), you get 5,625. So, the wind resistance at 75 mph is nearly DOUBLE what it is at 55 mph. Wind resistance is a HUGE drag on your mileage. And it's even worse if you drive some un-aerodynamic rolling hatbox, like an SUV.

RAY: So you're absolutely right, Frank. Driving slower will get you significantly better mileage. Unfortunately, I'm guessing that most people are still in too much of a hurry to heed your advice. Maybe when gasoline hits five dollars or six dollars a gallon, they'll slow down a little more and take some time to smell the diesel fumes.

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