Drafting

Discussion in 'Gen 2 Prius Fuel Economy' started by Whatsthat, Oct 18, 2005.

  1. Whatsthat

    Whatsthat New Member

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    I have seen drafting comments before so I thought I would add this info and see if others have noticed the same thing.

    First off I define drafting as 4 car lengths or more behind the truck. Any closer is just plain scarry.

    I drove from south Georgia to Greenville SC this past weekend and did some testing to pass time.

    I noticed that behind a normal 18 wheeler I got about 56 MPG over extended periods of time. Behind Tanker type trucks I averaged 62 MPG. Behind RV's only about 53. Behind car transport trucks fully loaded I got roughly 60 MPG.

    For the tank (620 miles) I averaged 59 MPG ((best ever for me))

    I was courious if anyone else has noticed this dramatic of difference?

    Disclaimer: I know that technically I needed a closed course with the same conditions, route etc. However, during my test I did switch back and forth behind different vehicles for 40 minutes at a time and saw immediate differences.
     
  2. Maytrix

    Maytrix New Member

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    Try it 2 car lengths away - I felt like I was being pulled.. I didn't stay that close for long though.
     
  3. aka007ii

    aka007ii New Member

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    I've been staying behind rigs because that's the only way to drive 65mph. I don't know if I can feel a pull but I'm not much for noticing subtle thing anyway. I just increased tire pressure and did a lot of surface street driving so I won't know about the drafting benefits for a while. I do have my best tank so far at 52mpg on break-in oil.
     
  4. Spunky

    Spunky New Member

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    How about you name me as the beneficiary on your life insurance policies? :huh:
     
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  5. IndyDoug

    IndyDoug New Member

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    I prefer to draft behind semi-trucks going less than 65MPH. Yes, there is a big improvement in MPG when you draft behind larger vehicles as opposed to driving alone on the highway.

    Keep in mind that not all truck drivers want you to draft behind them.
     
  6. DaveinOlyWA

    DaveinOlyWA 3rd Time was Solariffic!!

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    sorry, but you would be ticketed in a heartbeat in WA State. they just passed a law banning that and have had emphasis patrols all summer long and they are BUSY...

    i applaud the law because its obvious that it is definitely necessary
     
  7. Aerich

    Aerich New Member

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    It sure is necessary (to make those anti-tailgating laws). Idiots like aero engineers (me) do really lunatic drafting experiments "in the name of science."

    On the way home from the dealership (I had a very long way to go), it occurred to me that the instantaneous mileage values could be useful. So I drafted a big rig on the Capitol Beltway. We were going 70-75 mph. I got less than two carlengths for sure and definitely felt pulled. I knew I was in the vortex flow. I got somethinglike 80 mpg (instantaneous).

    I was pretty scared, but I tried side drafting too. I don't recall getting any effects from the slip stream. I've gotten some good effects on my Harley when slip streaming. (But the truckers REALLY hate that. They can see you sometimes.)

    I haven't... um... felt the need to further my experiments with the slip stream and vortex flows. But it would be interesting to see what changes one gets when driving different speeds, driving in cross-winds, driving behind a truck with a different profile, driving different car lengths... wow, maybe I'll go out now! (Not! ... no, really, I'm not...)

    Aerich the Rocket Scientist
    Alexandria, VA
     
  8. p626808

    p626808 New Member

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    I have been trying drafting techniques myself.. Best mpg increases are from 18 wheelers.. followed by buses.. and then big box trucks..
    I can gain 10-20 percent depending on speed..
    I do about 3-4 car lengths..

    Scott
    04 Silver#5 37K miles
     
  9. usnavystgc

    usnavystgc Die Hard DIYer and Ebike enthusiast.

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    I noticed a serious difference. I was on I-65 doing my usual 65mph in the slow lane and a dually truck towing a Wells Cargo trailer passed me. So I tucked in behind him for a while to see the results. He was going 75 (must have had his cruise set).

    The first 15 minutes of the pic is 65mph (cruise set, no drafting). The second 15 is 75 mph (cruise not set, drafting).

    I do not recommend this to anyone!!!!! You will be playing with fire. Kids, don't try this at home.

    PS: I know the pic is blurry but, you can get the general idea.
     

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