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Elevation Change Consumption Calculation for Roadtrips

Discussion in 'Technical' started by emir-t, Aug 11, 2017.

  1. emir-t

    emir-t Member

    Oct 28, 2013
    Hello all;

    I don't remember where but I remember reading a calculation about elevation change's effect on your consumption. I think it was a Bjorn video but can't find it now. This is a very simplified and noob calculation (I'm not an engineer so this is all 'internet knowledge') but I would like to know if it more or less works as I have a 260km road trip coming up this weekend including a bit of a climb with a BEV BMW i3 towards the end. That is a pure 19kWh usable energy, pathetic but what we have.

    So it goes;

    'weight of the car' x 'climbing altitude' x 'gravity constant' gives you, in joules, energy required for that climb. Divide it by 3,600,000 you get kWh. Also you add to that your regular flat road consumption for the lenght of the road spent climbing. For example with my upcoming roadtrip in the BMW i3;

    Car weighs 1300kg incl. me.
    I will climb 1200m in 60km
    Gravity is 9,8m/s

    So 1300 *1200 * 9,8 = 15,28 million joules required.

    Let's say the car is 85% efficient so I need 18million joules. In other words 5kWh.
    Lenght of the climb is 60km. And my flat road consumption would be 150wh/km. So 9 additional kWh needed for that.

    9+5 = 14kWh. + 10% error margin = 15,5kWh needed for the trip. So around 75-80% charge should be doable.

    On the way back I will have 15 million joules of potential energy. If I can harvest it with regen only at 70% efficiency I get 10,5 million joules, a.k.a 3kWh. So I should gain around 15% SoC on the way back with i3's tiny battery.

    Anyone want to chime in? Is the calculation making any sense to base a roadtrip on? Thoughts appreciated.
  2. kort677

    kort677 Banned

    Sep 17, 2015
    do you realize that this is a site aimed at tesla owners? wouldn't a better forum for your inquiries regarding a bmw i3 be better suited for a site that is focused on that vehicle?
  3. malcolm

    malcolm Active Member

    Nov 12, 2006
    Woah there kort!

    Hi emir-t, you've come to the right place. :)

    Thanks for the post.

    There is a ballpark figure I had about 4 years ago. 5kWh per 1000 feet???? Dunno. Would need to look it up.

    But that was for a rear motor Tesla S (or maybe even the Roadster) so not much use to you.

    Things change fast - even on Tesla-time (don't ask)
  4. SageBrush

    SageBrush 2018: Drain the Sewer

    May 7, 2015
    I agree with the trip up, presuming 1200 meters NET

    Back depends on how you use the potential energy. As kinetic energy pretty much all will be recovered; as regen, perhaps 50%
    I live in the mountains and play with potential energy frequently. My best tactic is to bleed off speed with coasting before I hit the apex so that I don't collect too much speed on the downhill and have to either brake or suffer higher Aero losses.
  5. ggr

    ggr Roadster R80 537, SigS P85 29

    Mar 24, 2011
    San Diego, CA
    5-6 MILES per 1000' elevation. And you get 4 of them back on a round trip.
    • Like x 1
  6. malcolm

    malcolm Active Member

    Nov 12, 2006

    Knew there was a 5 in there somewhere :)

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