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Does driving speed make THAT much difference?

Discussion in 'Model S: Driving Dynamics' started by Hookemhorns, Jun 14, 2016.

  1. Hookemhorns

    Hookemhorns Member

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    Looking at the mileage estimator Tesla used to have on their website, checking the range of a 70D. On a nice day (70 degrees), range at 80mph was about 200 miles; range at 55 mph was about 300 miles. I'm really rounding the numbers, but the difference to me is big! Would I really get about an extra 90-100 miles by slowing down that much?

    I've read that on a trip "the faster you go, the longer it takes" in a Tesla, since higher speed gets you to the SC sooner, but you have to spend more time charging. Seems like driving at a moderate speed has a lot of winners with no downside: safer; less stressful driving; more time in your comfortable, fun car; significantly less range anxiety; total trip time is the same.
     
  2. NOLA_Mike

    NOLA_Mike Active Member

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  3. DrManhattan

    DrManhattan Member

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    Which makes me wonder: Am I supposed to drive fast enough so that my SOC is low by the time I arrive at the next Super Charger? Meaning should I driver faster on purpose to use more charge?
     
  4. NOLA_Mike

    NOLA_Mike Active Member

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    The advantage to doing that is you get a faster charge rate at the supercharger.

    In a perfect world the answer is "yes" you should attempt to arrive at the next supercharger with the lowest SOC you are comfortable with. In reality there are many factors that affect range - speed, prevailing wind direction and speed, elevation changes, unexpected traffic incidents (including possible detours), temperature, etc. - that I seldom purposely cut it as close as single digits remaining range when I arrive at a supercharger. If I pull in to a supercharger with 25 miles remaining I think it's perfect.

    Mike
     
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  5. DrManhattan

    DrManhattan Member

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    Not a lot of detours on the 5 unfortunately! Wouldn't traffic actually give you more range anyway? I guess there isn't that much of a temperature range in California either. I guess wind/elevation change can still be a factor though. I guess 25 seems reasonable - but I may not have that luxury with a 60!
     
  6. Barry

    Barry Member

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    But officer, the forum told me I should drive faster... :)

    In my experience, the "break even" point for speed vs. charging time is about 75 mph. Any faster, and the battery depletes faster than the Supercharger can refill it. If your destination is home, it doesn't matter. If you're on a trip, and it's not the final stop of the day, it does.
     
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  7. David99

    David99 Active Member

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    It depends on the distance between two Superchargers. The longer the distance is, the more the greater energy usage forces you to charge to a higher state of charge where the charge rate gets slower.
     
  8. tstafford

    tstafford Member

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    My two cents - drive as fast as you can/want, stop at nearly all SCs if even just for a bit of juice and try to avoid putting yourself in a position where you have to charge beyond 80%.
     
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  9. linkster

    linkster Member

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    I thought it goes up by the velocity squared.
     
  10. TaoJones

    TaoJones Beyond Driven

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  11. chillaban

    chillaban Member

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    Yeah HUUUUGE difference. And I'll be the first to admit that in my ICE sports sedans I'm a lead foot and get anonymously close to triple-digits for road trips when the road permits. And fuel economy is barely worse and certainly a ton better than stop and go traffic.

    But no way, in my Model S, 75mph is pretty much the sweet spot for road trips. That already brings you below the EPA rated range by a hair. Going any faster than that results in monstrously lower range.... But the Model S's calm cruising demeanor and Autopilot should hopefully be motivation enough to travel at a leisurely pace and enjoy your trips rather than race to your destination.
     
  12. NOLA_Mike

    NOLA_Mike Active Member

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    Drag Force goes up with velocity squared. The Power required to overcome that goes up by the velocity cubed.
     
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  13. linkster

    linkster Member

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    #13 linkster, Jun 16, 2016
    Last edited: Jun 16, 2016
    Thanks. Still confused, your example in red shows 7.5 -> 60kw or 10hp -> 80hp?
     
  14. NOLA_Mike

    NOLA_Mike Active Member

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    It could but I'll give you an example where it did not.

    Last year I was traveling from New Orleans to New Jersey. At the time, there was one gap that didn't have a supercharger - Atlanta to Charlotte, NC and it was 245 miles from the Decatur Superchager to the Charlotte Supercharger. I range charged and left Charlotte with 249 miles rated range. I was going fine at 65 MPH and keeping my rated miles remaining above my actual miles remaining to go (I had a 4 mile buffer when I left but had increased it to a 12 mile buffer after about 120 miles in to the trip).

    Then I ran in to a big accident on the interstate wherein we just stopped on the interstate. After about 30 mins of being stopped running the A/C I lost 3 miles of rated range. Luckily we started moving again after 30 mins. and I made it - had we been stopped for hours I would have had to find another charging option to reach Atlanta.
     
  15. Sir Guacamolaf

    Sir Guacamolaf The good kind of fat

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    I learnt in school that reverse force due to viscosity increases ^4 to velocity. So yes that makes a HUGE difference!
     
  16. ecarfan

    ecarfan Well-Known Member

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    Yes. I really does make a big difference how fast you go.
     
  17. NOLA_Mike

    NOLA_Mike Active Member

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    Did you click the link that is the red? It will (should?) take you to the Wikipedia source from which it is a direct quote. I'm confused as to what you're confused about...

    Mike
     
  18. AmpedRealtor

    AmpedRealtor Active Member

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    Yes, absolutely. At higher speed there is greater wind resistance which is the #1 enemy of EVs. There is also the added electrical resistance, and therefore, losses at higher power output levels.
     
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  19. Owner

    Owner Active Member

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  20. shs1

    shs1 Member

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    The force related to aerodynamic drag goes up with the square of the speed, but if you go twice as fast, to travel the same distance you need to expend that energy in half the time, and therefore the power required to maintain that faster speed gets bumped up to a cubic function. However, because you are using that power for only half as long, the total energy used, and hence the effect on range, drops back to the square of the speed. If you try fitting any of the range vs speed curves, they can be fit fairly well with first and second order terms.
     
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