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Efficiency question re speed on hills

Discussion in 'Model S: Driving Dynamics' started by nleggatt, Aug 7, 2013.

  1. nleggatt

    nleggatt Member

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    When going up a steep hill is it more efficient to go slower than needed ie slower than limit, or just go speed limit up big big hill?

    Ie long long slow but steady outpu of energy or short but fast???
     
  2. jerry33

    jerry33 S85 - VIN:P05130 - 3/2/13

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    It's more efficient to lose a bit of speed as you go up. Ideally you try to find a steep hill that has a long gentle descent on the other side. Building some speed up before you start the ascent helps too.
     
  3. AC1K

    AC1K Member

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    Idealy you want to get enough speed to go up the hill without using power (so you will basically coast up but not regen up)
    when you peak the hill give the car a little power (like 5kW) and have the car accelerate downhill, break the speed limit if you have too but dont stop accelerating until you reach the bottom, then maintain velocity and keep your momentum, dont slow down for anything, run all stop signs and lights.
     
  4. nleggatt

    nleggatt Member

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    This is a 20 km steep uphill lol
     
  5. AC1K

    AC1K Member

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    wow 20kms, you may need to hit top speed then, no jk,

    for a constant incline try and go the lowest speed you can (but faster than 40), the more wind resistance the more drag, the worse millage, the absolute best speed for max distance is approx 40-50kph
     
  6. stevezzzz

    stevezzzz R;SigS;P85D;SigX

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    To expand a bit on jerry33's answer, when there are hills (even modest ones) it's more efficient to pretend you've got a car with a severely limited amount of power: watch the power meter and don't let the power consumption exceed some fixed value of your choosing, say for instance 40kW. If you do that, then on the uphills you will have to accept some slowing, maybe a lot of slowing if the hill is steep. On the downslope, don't let the speed exceed some fixed speed of your choosing, for grins let's call that number the 'speed limit'. Overall you'll achieve some average speed lower than the 'speed limit', but this technique will give you a small but significant improvement in efficiency over just setting the cruise control at that same speed.

    It's also to your advantage never to allow the car to go into regen braking (i.e., power meter in the green), though if the hills are anything but gentle, you can't avoid regen entirely.

    [edit: didn't see the '20kms steep uphill' comment before I posted this. It doesn't change the basic idea, though you may have to bump up the max power consumption you're willing to use in order to maintain a safe speed in the traffic conditions.]
     
  7. Gear

    Gear Member

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    The most efficient speed shouldn't really change much whether you're going up hill or on flat ground. The slower the better. Since there's no transmission, faster can't be more efficient. As the others said, if it's hilly, meaning up and down, then picking up speed on downhills and letting it bleed off on the uphill portions is the most efficient way to drive. I have a similar issue as I live in the mountains. If I let it coast leaving my house, I'd probably get up to 100+mph, so I figure I'll set the cruise at 60mph going downhill and hopefully get as much regen as I can to help offset the penalty of going back uphill later in the drive when I return home. There's no uphill after the long (20 miles or so) downhill, so there's no opportunity to just coast up the next hill for me. I'll have to figure it all out after I get the car, but that's just my theorizing at this point.
     
  8. brianman

    brianman Burrito Founder

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    1. The last sentence is incorrect at the limit. Going 0 gets you nowhere.
    2. Depending on the climate and the settings of your climate control system, sometimes slower is worse because of the longer usage of the climate control.
     
  9. Gear

    Gear Member

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    Well I obviously didn't mean it quite so literally. I believe the graph Tesla put out showed that 30mph or so was the ideal speed. Obviously there are other battery drains than just the electric motor, so it makes sense that the ideal isn't 1mph.
     
  10. stevezzzz

    stevezzzz R;SigS;P85D;SigX

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    Absolutely correct, brianman. As a practical matter, your no-heat/no-AC best-range speed would be slower than your summer (AC) best-range speed, which is slower than your winter (cabin and battery heating) best-range speed, everything else being equal. The first is roughly 25 mph for flat ground and no wind, IIRC, but what would the other two be?
     

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