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Drafting big rigs saves a minimum of 10 percent range

Discussion in 'Model S: Driving Dynamics' started by artsci, Aug 24, 2013.

  1. artsci

    artsci Sponsor

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    I'm on my first long drive -- 420 miles in two days, first leg 240 miles, most of it on I-95. I experimented with drafting large trucks. When I was drafting, mostly at 65-70 and 30-40 yards back, I was using about 1 mile of range for each mile traveled. When not drafting I was consuming about 1.1 to 1.15 miles of range per mile. So at those speeds there seems to be about a minimum 10 percent gain in range. Not scientific for sure but clear results.

    I've never drafted before but with a sufficient margin it actually felt safer nestled in behind a large truck. From there one gets a great vantage point for all of the foolish driving going on.
     
  2. RDoc

    RDoc S85D

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    I've wondered about that. Does the display show an instantaneous power value accurate enough to gauge the effect of how far back you are from the truck? Personally, I get a bit antsy if I'm less than one second behind a vehicle and prefer 2, but I suspect the drafting advantage falls off pretty rapidly. Most of the time around here you really can't follow further back than 2 seconds because someone will slide in front of you (and often then slow down).
     
  3. yobigd20

    yobigd20 Well-Known Member

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    I've done this lots of times...in my other cars. Yes it works. But I'm not going to drift a big rig in my Model S. I'm not cool with all the chips that it would put in the hood and the windshield. Yes I have Xpel Ultimate, but even that's not going to save you from the army of rocks you'll get hit with when drifting big rigs. I already got one that when right through the armor and the clear coat and the paint right down to the bare metal. It's tiny fortunately, but I can't imagine what it would've been without the paint protection.
     
  4. EarlyAdopter

    EarlyAdopter Active Member

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    #5 EarlyAdopter, Aug 24, 2013
    Last edited by a moderator: Mar 13, 2016
    Just be aware that the underride guards on most big rigs are inadequate and that rear-ending a truck will most likely be fatal, even in a Model S.

    This 2011 video from the IIHS is quite sobering.


    This 2013 video shows that while underride guards have improved on full-offset crashes, they still fail catastrophically on partial overlap.
     
  5. artsci

    artsci Sponsor

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    I don't pan to make a habit of this -- just wanted to test the effect on range. Fortunately there were no dings.
     
  6. Todd Burch

    Todd Burch Electron Pilot

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    Drifting a big rig would be uber-impressive ;)
     
  7. Jonathan Hewitt

    Jonathan Hewitt Active Member

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    I actually took my Model S on the interstate first time yesterday so no data yet. Based on past driving I do like to "follow" big rigs though. "follow" being drafting at a distance. Even at a safe distance (where you can see their mirrors aka they can see you) you can notice some gains. Semi trucks drive more predictably, too, so I consider it safer than following a different type of vehicle.

    As far as the Model S I'm not sure I want the front of my car eaten up by rocks, though I do have a clear bra. If it means making it or not making it to the next charger then I guess it's an easy decision. Otherwise it might be worth time charging not to have the potential damage. Definitely not worth the money saved, especially if you are using free supercharging ;)
     
  8. dhrivnak

    dhrivnak Active Member

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    And in many places it is illegal as I found out last year with my first ticket in more than 20 years. $15 fine but $75 in mandatory court fees, plus a lost half hour while the cop checks everything out.
     
  9. vfx

    vfx Well-Known Member

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    This is my preferred method for long range EV fuel economy. Faster point to point with similar range as driving below 55.
     
  10. lloyds

    lloyds Member

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    Safety aside, there's also the crud that gets kicked up from their tires that can crack our expensive windshields.
     
  11. Gear

    Gear Member

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    #12 Gear, Aug 25, 2013
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    I'm not so sure rear-ending a semi is a big concern. Unless you're completely absent-minded, there shouldn't be a situation where you can't out-brake the semi in front of you, especially not at any significant speed differential. I'd personally worry about rocks and debris as others have mentioned, and especially about retread coming off. You see chunks of retread along the side of the road all the time because they constantly blow off semi tires. Those large rubber chunks can do a good amount of damage. As somebody else mentioned, I'd only draft a semi if it was the only way to make it to the next charging station.

    - - - Updated - - -

    Indeed!

     
  12. gnelson

    gnelson Member

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    #13 gnelson, Aug 25, 2013
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  13. hans

    hans P631

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    Adaptive cruise control would be a nice to have because then we could set up a convoy of Tesla's all drafting each other like the peloton in a bike race.
     
  14. Todd Burch

    Todd Burch Electron Pilot

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    #15 Todd Burch, Aug 25, 2013
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    Meh. Where's the trailer?

    (Just kidding. That was fun to watch).

    I've found that even following behind vans/SUVs at a fairly normal distance has noticeable benefit.
     
  15. bhzmark

    bhzmark Active Member

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    Yes adaptive cruise makes drafting a piece of cake and very safe. It's simply a matter of picking which vehicle to be behind. There has to be something in front of you -- it might as well be a vehicle that leaves a wake that you can take advantage of.
     
  16. Doug_G

    Doug_G Lead Moderator

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    Absolutely, yes, drafting a large truck works. It allows you to drive 10 mph faster for the same power consumption. But do it carefully and responsibly!
     
  17. brianman

    brianman Burrito Founder

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    Hmm...
     
  18. EarlyAdopter

    EarlyAdopter Active Member

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    #19 EarlyAdopter, Aug 28, 2013
    Last edited by a moderator: Mar 13, 2016
    If they have a load, you are correct that you will be able to out brake them... assuming you notice in time. If they do not have a load, you are incorrect. Can you tell the difference when drafting which is which? Is this a gamble you really want to take, given the potential consequences. Note that the IIHS crashes were at just 35 mph, not that big of a differential.

    Also, you better hope the truck doesn't have collision avoidance radar and panic brakes. That wouldn't leave you a whole lot of reaction time, even with a full load as in this video:



    All I'm trying to point out is the consequences of rear ending a semi are drastically worse than rear ending a passenger vehicle. Many people here may be unaware of those risks. I certainly was. Those IIHS videos were eye opening to me.
     
  19. mnx

    mnx 2013 P85

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    Drafted a truck on a trip I took this week and got some of my lowest Wh/km #'s I've seen. I'm not sure I was even following him for the full 50km.

    IMG_20131002_122447.jpg
     

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