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Ideal travel speed in RWD?

Discussion in 'Model 3' started by SlicedBr3ad, Jul 22, 2018.

  1. SlicedBr3ad

    SlicedBr3ad Member

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    Has anyone done or could help with this analysis?

    What is the fastest speed we should use on m3 to get somewhere far (1000+ miles) while using only superchargers to charge up in order to get somewhere in the shortest amount of time?

    I.e. driving 90 mph in m3, battery loses about 30% so it takes 150 miles of charge to go 100 miles. Then it takes ~20 mins to charge those 150 miles of battery. So in effect, you spend ~85 minutes to go 100 miles which averages to ~70 mph (drive+charge) speed. Eg 65 minutes to drive 100 miles and 20 minutes to charge= 85 minutes to travel 100 miles. What happens when's driving 80, 70, 60 instead of 90?
     
  2. DriveMe

    DriveMe Member

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    #2 DriveMe, Jul 22, 2018
    Last edited: Jul 22, 2018
    Youtuber Bjørn Nyland did that type of tests and measurements in his Model X on a German Autobahn and found 93 miles per hour to be the optimal driving speed in his Tesla. :)
    In other words, high speed is not a concern on a longer trip! It does not increase the trip time.
    That's for model X. But since Model 3 has better aerodynamics, I would expect a similar conclusion.
     
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  3. DriveMe

    DriveMe Member

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    Here is the link to Bjørn's video:
     
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  4. SlicedBr3ad

    SlicedBr3ad Member

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    Yes, would love to have this for model 3 to optimize long distance travel.
     
  5. Arpe

    Arpe Member

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    Model 3 has to be pretty much the same. What you have to look at is the charging speed curves. The charging rate is capped out at around 115 kW from 10-50% and then gradually fades off. The fastest way to drive your Model 3 is then to hit the supercharger at 10-20% charge every time you are having a stop.
    To get to the supercharger at 10-20% charge you have to match your speed accordingly, although I don't think you will benefit from driving above 100 mph (wind resistant is rather dominant on range).

    Charging characteristics:
    Supercharger speed: 116kW
     
  6. SageBrush

    SageBrush 2018: Drain the Sewer

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    #6 SageBrush, Jul 22, 2018
    Last edited: Jul 22, 2018
    Models support higher speeds but only if additional supercharger stops are not incurred and the driver stays in the fast part of the charging curve. As @Arpe says, the practical way to do this is to match speed to arrival to the Supercharger at ~ 10%. Be careful of wind and poor roads though, as these are not accounted for in the map's SoC arrival estimate. I personally would probably play the speed game during my last 1/3 of the distance to the Supercharger to drop arrival SoC from 20% to 10% to avoid unhappy estimates.
     
  7. ForeverFree

    ForeverFree Supporting Member

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    Recently returned from a road trip from LA to Park City, Utah.

    Was surprised to discover that Interstate speed limit there was 80.

    Turned out that traveling 85 was the way to go, at least in a 3. Driving time saved exceeded Supercharging time added (at 8 miles/minute in heart of charging curve). Of course, it helped that Superchargers were optimally spaced, and that they were easy-on, easy-off freeway (except for St. George).

    Scenario-checking on abetterrouteplanner.com confirmed this.
     
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  8. SageBrush

    SageBrush 2018: Drain the Sewer

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    #8 SageBrush, Jul 22, 2018
    Last edited: Jul 22, 2018
    Here is the result I obtained. The graph is dense because car speed and Supercharger rate are both in play.
    Each group on the graph is a certain Supercharger speed, and the bars represent speeds at a certain mph.

    People may find it easiest to read the graph by asking "At e.g 60 kW charging rate, can I save time by increasing speed from 70 to 75 mph ?" If the 75 mph bar in the 60 kW group is greater than zero, time is saved. The optimal speed is at the transition from positive to negative value. Here is the data.

    upload_2018-7-22_12-51-42.png

    Addendum:
    I calculated the incremental power as Aero only, but on second thought I should also include incremental rolling losses. I'll update the graph later. The result will be a modest drop in optimal car speed.
     
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  9. RayK

    RayK Member

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    I hate word problems. ;)
     
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  10. chronopc

    chronopc Active Member

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    Not sure I"m reading the chart right, but is it saying that 70mph is the optimal speed?
     
  11. Saghost

    Saghost Well-Known Member

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    In principle, for a trip of unlimited length, the fastest speed will occur when the driving time and charging time equalize. With Superchargers, you can't drive the car that fast physically, let alone legally/safely. The extra time you spend charging due to reduced efficiency at higher speeds is more than matched by the decreased driving time.

    So for the shortest trip time in general, drive the fastest speed you feel is safe/legal, assuming you have lots of Superchargers available.

    That's the general case, though. There can be exceptions for trips of lengths where you might avoid a charging stop (depending also on how you feel about doing a small partial charge,) or for cases where the Superchargers aren't positioned conveniently for the speed.
     
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  12. SageBrush

    SageBrush 2018: Drain the Sewer

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    No, look at the transition point
     
  13. SageBrush

    SageBrush 2018: Drain the Sewer

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    I'm scratching my head wondering why that is true.

    Addendum: I got it. elegant !
     
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  14. SlicedBr3ad

    SlicedBr3ad Member

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    So everyone drive 70 mph or am I reading it wrong?
     
  15. Big Earl

    Big Earl Supporting Member

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    #15 Big Earl, Jul 22, 2018
    Last edited: Jul 22, 2018
    You’re reading it wrong.

    The fastest speed is where the bar on the graph is at neutral. At a 75 kW average charge speed, your ideal travel speed is between 95 and 100 miles per hour. If you have a Model 3 long range or S/X 100 and you’re averaging over 110 kW, your ideal travel speed is closer to 105 miles per hour.

    You can experiment with various trip parameters on http://www.abetterrouteplanner.com
     
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  16. David99

    David99 Active Member

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    The ideal speed is much faster than you can legally and safely drive in the US. In other words drive as fast as you can but stay within a safe and legal limit, please!

    Two other things to consider, though: The Model 3 charges slower when the battery is almost empty and of course when the battery is almost full. So it's best to aim to arrive above aprox 8% and don't charge more than you need to get to the next Supercharger. If you charge more than you need to reach the next one, your charge rate drops and you lose time overall.

    When the distance to the next Supercharger is very long and you need almost your entire battery capacity there is a tipping point where driving slower helps saving time overall instead of charging to 100% and wasting a lot of time on the last few %. For the Model 3 that point is aprox 15 kW. Once the charge rate drops below 15 kW at a Supercharger and you already have enough to reach the next one, you might as well start driving and adjust your speed so you make it. Charging more will give you more energy and you could drive faster but you are spending more time at the charger than you can make up with speed.

    Another tip: It is not always better to skip a Supercharger to save time. If you skip one and have to charge to 80 or 90% you are wasting time because the charge rate drops down. If you stop at the Supercharger in between, you can charge less and stay in the range where the charge rate is higher. It will save time overall even though you are adding a stop. This seems counter intuitive and annoys the heck out of my family, but does make sense looking at the numbers.

    evtripplanner.com is a great tool to test things out.
     
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  17. SlicedBr3ad

    SlicedBr3ad Member

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    Thank you. Sounds like charge often as long as battery is below 50 and don't let it go above 80%, start driving.
     
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  18. SlicedBr3ad

    SlicedBr3ad Member

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    Well, this just encourages to do the wrong thing as safely as possible.
     
  19. Saghost

    Saghost Well-Known Member

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    This is one of the things you have to watch for when using the Nav system's trip plan. For some reason (shorter overall distance?) the current Navigation code tries to minimize stops, planning 50 minute charges deep into the taper and skipping over Superchargers where possible. The car's plan is always executable in my experience, but often not the quickest or most convenient.

    (Hopefully one of these days we'll get the fastest/shortest/least energy/fewest turns routing priority options in the Tesla Nav system, now that it's been moved to a modern code base. Edit: And Waypoints, and trip planning on the phone uploaded to the car. This is one of the places Tesla could really show off with their OTA updates and general connectedness.)
     
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  20. Big Earl

    Big Earl Supporting Member

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    The magic range is 10% to 55 or 60%.
     
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