Drafting = 3 mpg increase

Discussion in 'Gen 2 Prius Fuel Economy' started by electricity_guzzler, May 25, 2006.

  1. electricity_guzzler

    electricity_guzzler New Member

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    If i do cruise control 65mph I get about 48 mpg. But when I tried drafting 1 to 2 car-lengths behind SUVs at 70 to 80 mph, I get better gas mileage, about 3 mpg more.

    This makes sense to me because air resistance is mainly what your spending energy on at highway speeds. At 65 mph cruise control, I'm the slow car and everybody passes me, so I'm not in anybody's draft and i'm getting the full frontal air resistance. If I drive with traffic even at a faster speed, I get less air resistance because I'm following another car's wake.

    tip: look for SUV drivers talking on their hand-held cell phones. they tend to drive at a constant speed. whereas those who are not distracted tend to accelerate/decelerate often. also drivers on cell phones tend not to change lanes when somebody is drafting them. drivers who are not distracted will think that you want to pass and either accelerate or change lanes.
     
  2. NuShrike

    NuShrike Active Member

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  3. MikeSF

    MikeSF Member

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    tip: don't tail gate anyone that's just bad karma, get your fuel efficiency elsewhere... like driving less than 70-80mph. prius owners dont like it when SUVs tailgate them, I doubt they like very much anyone tail gating them
     
  4. burritos

    burritos Senior Member

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    <div class='quotetop'>QUOTE(MikeSF @ May 25 2006, 06:56 PM) [snapback]261092[/snapback]</div>
    Maybe all them suv's that tailgate us are just drafting to improve their crappy mpg?
     
  5. cwerdna

    cwerdna Senior Member

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    I think what the OP is suggesting is a very bad practice and potentially very dangerous. One car length is too close at those speeds. Two is somewhat marginal but you sometimes can't help it due to congestion.

    I try to drive defensively. (reminds me that I should try to look around for a defensive driving course) Personally, if I can help it if there are multiple lanes, I like to have a LOT of room in front of me. I try to switch to empty lanes when possible or to lanes where I have a LOT more room in front of me.

    Even if the increase in mileage were 50%, I don't think it'd worth the danger. An accident could cost you a heck of a LOT more than what the gas savings over the life over the car.
     
  6. electricity_guzzler

    electricity_guzzler New Member

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    WOW! I just tried drafting behind an 18-wheeler this morning. incredible mpg gain. 10mpg more. The good thing about drafting big trucks is that you know they cannot brake faster than you can. From now on, i'm taking the truck lanes everyday!
     
  7. DaveinOlyWA

    DaveinOlyWA 3rd Time was Solariffic!!

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    you are playing with fire
     
  8. KD6HDX

    KD6HDX New Member

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    I tried this morning following a 40 foot trailer. He was driving 55 MPH. Sometimes he was slowing down to 51-52 and then back up to 55MPH. Two to three car lengths at this speed did seem to give a little more MPG on the MFD. But it was over a half hour period on the way to work this morning. Overall, I would say it is a risky bet for a few pennies gained. Especially at 70 or 80 MPH. My wife was asleep on the commute this morning. Had she been awake I would never have tried this experiment. A little later down the freeway, I pulled in behind another prius in the slow lane going 52 MPH. I stayed behind him for about 10 miles. The slower speeds are what I think are giving the increased MPG's. Like I have said in the past, when I drive tha carpool lanes at 70 MPH, I get about 48 MPG. When I slow down and cruise at 55, I get about 53 MPG. I will not cruise at 55 mph in the carpool lane. This really pisses off people and since I live in So Cal, I may not be able to reload fast enough! ;)

    The best way to streamline the prius is to fold back its rear view side mirrors. This reduces the drag coefficient even more. Plus it makes the car look more goofy and people around you will slow down too when they try to tell you your mirrors are folded back.

    Dave 2005 PRIUS
    Reducing my dependency on American oil from foreign lands one goofy little car at a time....

    GO BIG ED ON AIR AMERICA
     
  9. hycamguy07

    hycamguy07 New Member

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    <div class='quotetop'>QUOTE(electricity_guzzler @ May 26 2006, 10:24 AM) [snapback]261292[/snapback]</div>
    Here its 181.50 + 4 points on your license.. :eek:

    The only difference is other people call in on their cellphones and follow you until an officer arrives :huh:

    Another cool thing for drafters is running over tire sherapnel and 1 -2 car lengths is not enough reaction time before the drafter hits the debris.. :lol: :lol:
     
  10. brandon

    brandon Member

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    <div class='quotetop'>QUOTE(electricity_guzzler @ May 26 2006, 09:24 AM) [snapback]261292[/snapback]</div>
    Of course, that doesn't matter much if when they can't see that you're riding their a$$ behind their trailer. Even if they hit the brakes, you still have to allow yourself enough distance that you can react to it. Please re-read posts on other threads where you were advised to drive defensively...

    We're not trying to put you out, we just don't want you going out and killing yourself and/or others for the sake of a few extra MPG.
     
  11. LowCO2

    LowCO2 New Member

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    <div class='quotetop'>QUOTE(KD6HDX @ May 26 2006, 09:51 AM) [snapback]261302[/snapback]</div>
    Nice comments Dave! :D
    From one ROOKIE poster to another
    (Charlie)
     
  12. electricity_guzzler

    electricity_guzzler New Member

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    <div class='quotetop'>QUOTE(brandon @ May 26 2006, 12:30 PM) [snapback]261344[/snapback]</div>
    i'm following 2 car lengths behind the trucks. this is normal following distance in NJ highways. I'm not doing anything crazy like tailgaiting 1 foot behind.

    there is no way that an 18-wheeler can stop faster than I can even with only 2 car lengths reaction time. i'm more worried about the 18-wheeler BEHIND me than the one i'm drafting.

    btw i'm a very skillful driver. never had an accident and i drive 35000 miles a year. of course i don't recommend anyone to drive beyond their ability.
     
  13. Betelgeuse

    Betelgeuse Active Member

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    <div class='quotetop'>QUOTE(electricity_guzzler @ May 26 2006, 01:53 PM) [snapback]261387[/snapback]</div>
    OK. So, what happens when the truck you're driving behind hits a truck in front of him? At 65 MPH, you can close 20 feet (~2 car lengths) in 0.2 seconds. Two car lengths is far too little at highway speeds. It's dangerous, illegal, and you're going to really piss off a trucker pretty soon.
     
  14. NuShrike

    NuShrike Active Member

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    <div class='quotetop'>QUOTE(Betelgeuse @ May 26 2006, 11:44 AM) [snapback]261415[/snapback]</div>
    Well, brake then. If the truck is going to brake that hard, it's going to jack knife and you're frelled anyways within 150 feet.

    In places like LA where traffic tends to be a huge cluster frell, 2-3 car lengths of space is the exception and 1 is more the general rule.

    Why? Not only are there just too many cars here, and rush hour patterns stretch pretty much from early morning until evenings now. Worst on Fridays, lighter on Mondays. Light traffic only happens in the middle of the night. So, during the "regular rush hours" if you have more than 1.5 car lengths expect that to be 0.5 car lengths very very soon because somebody is going to cut in. What happens if there's sudden braking when somebody is cutting in?

    My defensive driving is it's more dangerous to let somebody cut in than to just manage the space myself.

    The rule seems to be follow as close as the vehicle is high. Good thing 18-wheelers are high.
     
  15. DaveinOlyWA

    DaveinOlyWA 3rd Time was Solariffic!!

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    i think the point everyone is trying to make is that it doesnt matter how fast either of you can stop if you hit the truck before your foot hits the brake
     
  16. Presto

    Presto Has his homepage set to PC

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    I tried drafting trucks on the highway and unless the wind direction really is going against me, i can usually get 20-50% better fuel economy. I didn't need to be too close to take advantage of the draft... 2 seconds distance was just fine.
     
  17. MikeSF

    MikeSF Member

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    Wern't they testing a computer drive program on a patch of road in SoCal? What ever happened to that? I know many people were complaining about "how they never would let a computer drive their car..." me on the other hand I say go for it, 1) you go through traffic WAY quicker than even car pool lanes, this alone could convince many to allow what they ordinarily wouldn't, 2) the drafting alone is a gas saver.

    Oh well so much for the independance of the american driver.
     
  18. Mr. Tuco

    Mr. Tuco New Member

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    Sure, you could get a few more mpg drafting behind semi trucks, but at what cost? The money saved on gas will be insignificant compared to tire retread damage, rock chips (on paint and wind shield) or worse yet, an accident. Not worth it!
     
  19. sabiking

    sabiking New Member

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    Drafting definitely has it's benefits ;) I recently was given this stuff called Ethos which I added to my gas when I filled up and now am averaging 59 mpg @ 75 mph. I LOVE THIS CAR! :D Just wish it came in a truck version so I could use it for fishing too.
     
  20. hobbit

    hobbit Senior Member

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    Following a semi at *proper* distance also gives MPG benefits, since
    the truck is still pulling a bunch of air along with it even that
    far back. Any closer is definitely not recommended, I don't care how
    good you think you are.
    .
    _H*
     
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