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    NEW YORK (CNNMoney.com) -- With gas prices rising, gas-saving advice abounds: Drive more gently, don't carry extra stuff in your trunk, combine your shopping trips.

    This is all sound advice but there's one driving tip that will probably save you more gas than all the others, especially if you spend a lot of time on the highway: Slow down.

    In a typical family sedan, every 10 miles per hour you drive over 60 is like the price of gasoline going up about 54 cents a gallon. That figure will be even higher for less fuel-efficient vehicles that go fewer miles on a gallon to start with.

    The reason is as clear as the air around you.

    When cruising on the highway, your car will be in its highest gear with the engine humming along at relatively low rpm's. All your car needs to do is maintain its speed by overcoming the combined friction of its own moving parts, the tires on the road surface and, most of all, the air flowing around, over and under it.

    Pushing air around actually takes up about 40% of a car's energy at highway speeds, according to Roger Clark, a fuel economy engineer for General Motors (GM, Fortune 500).

    Traveling faster makes the job even harder. More air builds up in front of the vehicle, and the low pressure "hole" trailing behind gets bigger, too. Together, these create an increasing suction that tends to pull back harder and harder the faster you drive. The increase is actually exponential, meaning wind resistance rises much more steeply between 70 and 80 mph than it does between 50 and 60.

    Every 10 mph faster reduces fuel economy by about 4 mpg, a figure that remains fairly constant regardless of vehicle size, Clark said. (It might seem that a larger vehicle, with more aerodynamic drag, would see more of an impact. But larger vehicles also tend to have larger, more powerful engines that can more easily cope with the added load.)

    That's where that 54 cents a gallon estimate comes from. If a car gets 28 mpg at 65 mph, driving it at 75 would drop that to 24 mpg. Fuel costs over 100 miles, for example - estimated at $3.25 a gallon - would increase by $1.93, or the cost of an additional 0.6 gallons of gas. That would be like paying 54 cents a gallon more for each of the 3.6 gallons used at 65 mph. That per-gallon price difference remains constant over any distance.

    Engineers at Consumer Reports magazine tested this theory by driving a Toyota Camry sedan and a Mercury Mountaineer SUV at various set cruising speeds on a stretch of flat highway. Driving the Camry at 75 mph instead of 65 dropped fuel economy from 35 mpg to 30. For the Mountaineer, fuel economy dropped from 21 to 18.

    Over the course of a 400-mile road trip, the Camry driver would spend about $6.19 more on gas at the higher speed and Mountaineer driver would spend an extra $10.32.

    Driving even slower, say 55 mph, could save slightly more gas. In fact, the old national 55 mph speed limit, instituted in 1974, was a response to the period's energy crisis.

    It was about more than just high gas prices, though. The crisis of the time involved literal gasoline shortages due to an international embargo. Gas stations were sometimes left with none to sell, and gas sales had to be rationed. The crisis passed, but the national 55 mph speed limit stayed on the books until the law was loosened in the 1980s. It was finally dropped altogether in 1995. (The law stuck around more because of an apparent safety benefit than for fuel saving.)

    Despite today's high gas prices, don't expect to see a return to the national 55 mph speed limit. The law was unpopular in its day, and higher speeds have become so institutionalized that even the Environmental Protection Agency's fuel economy test cycle now includes speeds of up to 80 mph.

    Driving 10 miles per hour faster, assuming you don't lose time getting pulled over for a speeding ticket, does have the advantage of getting you to your destination 50 minutes sooner on that 400 mile trip. Whether that time difference is worth the added cost and risk is, ultimately, up to you.

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    1 - 20 of 188 Comments
    lilcayte1 Jul 28, 2009 8:12 PM
    well it doesn't matter if you drive stick because driving stick saves you gas on the highway and wastes gas in the city, so for that 400 mile drive your good and for the traffic in the city you're not really saving more like wasting
    Report This
    randelg Jul 28, 2009 5:24 PM
    The $3.25 per gallon was the price used in the article. Don't know when their research was done, but at the $2.49 per gallon price, I'd still spend $5.85 more.
    Report This
    ronkoehler Jul 28, 2009 4:25 PM
    What's this $3.25 a gallon? It's only $2.49 a gallon here, so its already less expensive than going slower would be.
    Report This
    srich37 Jul 28, 2009 2:16 PM
    Read the article. At the end it does say it will take longer. You are obviously in one heck of a hurry. This article, if you are at all concerned about wasting money and being smartly conservative, is just that; a lesson in being conservative and being more environmenally frugal. Everyone spends all this time hurrying from point A to point B, as environmental stewards we need to be more intelligent. That is all this is telling us. It is correct on the AVERAGE car. Each car has a different set of criteria. As with the stock car. It is more efficient if driven at higher speeds and higher RPMs. The study is an average guys. The idea thta there are NO accidents with NO speed limit....talk about stupid. It hads less to do with speed limits than it does with the drivers and our mental state. Those drivers not in a hurry or under less stress have less accidents. Speed is less of a factor. Look at other countries and see how there are less accidents.
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    ferguson550 Jul 28, 2009 2:11 PM
    Forgot to add about testing on hills. Actually it's about the same. And to that person saying going faster saves money because your engine is not running as long. Gas mileage is measured in gallons and mileage, not time.
    Report This
    brocknv Jul 28, 2009 2:10 PM
    I would think the gear ratio would be a huge factor
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    ferguson550 Jul 28, 2009 2:07 PM
    All you people saying your car gets better mileage the faster you go are wrong. If you are measuring your mileage by the old fill it up and subtract the odometer mileage then you are never going to get an accurate measure. Some pumps vary, gas swellswhen hot, etc. My car has an electronic gas mileage monitor and that is the onlly way you can accurately measure mileage on the fly. My car(a 2007 Ford Fusion with V-6 gets about 31 at 55 mph with air on and no hills. At 65mph it drops to about 29 so the article is pretty close. At 75 it drops to about 27 and at about 45 mph it goes up to about 33. You people saying the faster you go the better mileage you get are not measuring accurately. I notice the people saying this have an older car made before the advent of on board computer gas mileage monitors.
    Report This
    randelg Jul 28, 2009 2:05 PM
    To kixaholeinthesky...I did the math, relating to the extra time the engine is running vs. the higher fuel consumption. In my Honda CRV, I would still spend $6.10 more to travel the 400 miles at the higher speed. That's assuming their $3.25 per gallon and 4mpg difference at the higher speed.
    Report This
    jjlongo Jul 28, 2009 2:04 PM
    This is BS. Each car is different. My 6 cylinder S-10 pickup is most efficient at 65MPH. My 2006 Jetta TDI runs at peak efficiency at 75MPH. 2004 8 cylinder Caddy peaks at 65 MPH, 4 cylinder Ford Tempo has a peak at 55 MPH . . . Not sure who where this info was derived from, ******** wrong.
    Report This
    jjlongo Jul 28, 2009 2:04 PM
    This is BS. Each car is different. My 6 cylinder S-10 pickup is most efficient at 65MPH. My 2006 Jetta TDI runs at peak efficiency at 75MPH. 2004 8 cylinder Caddy peaks at 65 MPH, 4 cylinder Ford Tempo has a peak at 55 MPH . . . Not sure who where this info was derived from, ******** wrong.
    Report This
    yxk0012 Jul 28, 2009 2:01 PM
    Where was this test done? If it was done in a place where most people do 60-65 mph, driving at 75 would be very different from driving at 65. It would take more braking and accelerating to maintain 75 mph (which is why one lane camper does more damage to the environment than a few speeders). That's where most of that mileage difference came from. In California, where most people do 75, the difference is about 2-3 mpg, not 5 mpg (my observations in a 4-cyl. Camry). Which translates in $3-5/hr for your vacation time. It's really not worth it.
    Report This
    plentofdick Jul 28, 2009 1:58 PM
    What a joke. Every car is different, and each one has its leverage point where it gets the best mileage. Change tire size, and it moves, change engine size, and it moves. There is no set mph at which every car gets best mileage. This is the biggest crock of ***** i have seen in a LONG time. I build cars for a living, both drivers and race cars. Simply adding 5 psi in your tires can change mpg as much as 5 mpg. This study, or lack thereof fails entirely. As a ploy to get people to slow down. Stupid. Did you account for what my TIME is worth. i get there WAY faster at 80, than at 60. Sorry.... not slowing down. Ever see the study where traffic accidents dropp to ZERO when theres NO speed limit. YEAH, wake up sheeple.
    Report This
    plentofdick Jul 28, 2009 1:57 PM
    What a joke. Every car is different, and each one has its leverage point where it gets the best mileage. Change tire size, and it moves, change engine size, and it moves. There is no set mph at which every car gets best mileage. This is the biggest crock of ***** i have seen in a LONG time. I build cars for a living, both drivers and race cars. Simply adding 5 psi in your tires can change mpg as much as 5 mpg. This study, or lack thereof fails entirely. As a ploy to get people to slow down. Stupid. Did you account for what my TIME is worth. i get there WAY faster at 80, than at 60. Sorry.... not slowing down. Ever see the study where traffic accidents dropp to ZERO when theres NO speed limit. YEAH, wake up sheeple.
    Report This
    prn13norm Jul 28, 2009 1:57 PM
    This study must have been done by the insurance companies.
    Report This
    cambokid562 Jul 28, 2009 1:55 PM
    This is so not true.Well maybe it is for certain cars with low hp and tq that rev too high at 75 mph.My IS350 would probably get more MPG cruising at 90 mph than a corolla because the revs are much lower at that speed while in 6th gear.But cruising at 55 mph where the revs on both cars are just about the same then yes the corolla would get the better mileage.Fuel efficiency is not so much about the actual cruising SPEED but more about the car itself and how high the engine revs at certain speeds when cruising.
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    lazybum03 Jul 28, 2009 1:54 PM
    power steering can take away mpg, well i'm an idiot and broke the ajusting bolt/lock nut mechanism for my ps belt....but yea i've seen 5-7 mpg increase on my commute to work....which is mostly on the interstate driving 16 miles, with about 6 miles of city driving....
    Report This
    cpman93 Jul 28, 2009 1:52 PM
    A simple fix that the automative makers should have jumped on right away is going to a six speed. They are starting to use them but you don't have to completely redesign a car to do it. I don't like the idea of the slap shifter at all. I drive sticks and automatics. If I'm looking for improving gas milage give me a 6 speed stick in a wider variety of cars.
    Report This
    planxan2 Jul 28, 2009 1:50 PM
    Quoting the article, "Over the course of a 400-mile road trip, the Camry driver would spend about $6.19 more on gas at the higher speed and Mountaineer driver would spend an extra $10.32." ___________ DO THE REST OF THE MATH! On a 400 mile journey at 65mph it takes 6 hours and 10 minutes, while at 75mph it takes 5 hours and 30 minutes. That's a savings of 40 minutes of driving time for about $8.00. Most people would pay $8 to not spend 40 additional minutes on the road. CASE CLOSED.
    Report This
    planxan2 Jul 28, 2009 1:50 PM
    Quoting the article, "Over the course of a 400-mile road trip, the Camry driver would spend about $6.19 more on gas at the higher speed and Mountaineer driver would spend an extra $10.32." ___________ DO THE REST OF THE MATH! On a 400 mile journey at 65mph it takes 6 hours and 10 minutes, while at 75mph it takes 5 hours and 30 minutes. That's a savings of 40 minutes of driving time for about $8.00. Most people would pay $8 to not spend 40 additional minutes on the road. CASE CLOSED.
    Report This
    jessbeau Jul 28, 2009 1:50 PM
    From what I remember from physics class, is that the perfect, air resistance to ground friction, the best and optimum speed for fuel consumpsion is 45MPH. Then it comes down to how constant you keep your foot on the gas pedal. you actually get worse gas milage in stop and go trafic then you would at 80MPH for over an hour.
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    1 - 20 of 188 Comments
     
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