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Highway Range Ignorance

Discussion in 'Model S' started by WhiteKnight, Dec 21, 2011.

  1. WhiteKnight

    WhiteKnight _____ P85 #549 _____ Sig Red / Sig White

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    When traveling at 75 mph (highway speeds) you get only 70% of the range you would receive at 55 mph. In addition the battery capacity is reduced by 30% after 6-9 years.

    Therefore your highway range (@ 75 mph) with an 85 kWh pack will be 210 miles initially and around the time the warranty expires it will be down to 150 miles.
    For the 60 kWh pack it's even worse. 230 miles is 160 to start, dropping to 115 or so.
    And for the 40 kWh pack you start at 115 on the highway and go to about 80 miles in range by year 8.

    The Tesla Model S, even with the biggest battery pack, is more of an intra-city car than an inter-city car.

    Under the best case scenario if you take the Model S on the highway you can drive for 2 hours and 50 minutes before you have to pull over for 1 hour to recharge. That's the biggest battery pack on the day that you bought the car. It only goes downhill from there. This is not going to be your road trip car.

    Source: Roadster Efficiency and Range | Blog | Tesla Motors (see spreadsheet)
     
  2. Tommy

    Tommy Member

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    WhiteKnight, your assumptions may be correct or they may be incorrect. The information you state as facts is taken from a 2008 blog posted about driving conditions for the Roadster; Can the same parameters can be assigned to the Model S? Drivetrain loses, tire rolling resistance, batteries and aerodynamics have all improved from when that data was collected. Sorry, but I don't make the connection on how the Roadster performed with its off the shelf cells in 2008 to a car engineered from the ground up to be an EV.
     
  3. NielsChr

    NielsChr Member

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    Lets see some real live numbers before we make any conclutions. afaik. the roadster owners is still satifyed with the range and haven't complaied about highway range.

    Tesla is still delivering the best perfomance/range EV car made jet of any car maker.
    2' to Tesla is the Leaf afaik., but this car have only 24 KWh battery compared to Tesla 85 Kwh battery - that is more than 3 times the capacity. Im pretty shure I know witch of the 2 will run out of juice first :)
     
  4. VolkerP

    VolkerP EU Model S P-37

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    #4 VolkerP, Dec 21, 2011
    Last edited: Dec 21, 2011
    Sure, old data, but we can do some guesswork.

    CdA is same for Roadster and Model S so we can reuse the aerodynamic drag Wh/mile figure from the Roadster (cyan line).
    [​IMG]
    At 55mph aerodynamic drag is responsible for 100 of 230 Wh/mile = 43%. Energy lost to aerodynamic drag will increase by square of speed, that is by 86% when going from 55mph to 75mph. Other losses are mostly independent of speed. Thus I arrive at 37% increase of energy consumption, or 1/1,37 = 73% reduced range. The OPs figure of 70% is in the same ballpark.

    Edit: I am aware that Model S might have higher ratio of rolling resistance vs. drag at 55mph due to increased vehicle mass. That would diminish the effect of going faster, though.
     
  5. Doug_G

    Doug_G Lead Moderator

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    Let's take my typical Ottawa-Toronto trip, a roughly four-hour ICE drive. With the Roadster I have to drive about 10 mph slower than I usually would, and do a two hour NEMA 14-50 charge. That's a bit inconvenient as it turns a ~4 hour trip into a ~7 hour trip.

    Part of the problem is that the KOA is poorly sited so I have to go to full Range mode, which is slower. If it were closer to the midpoint I could knock at least half an hour off. If that was an HPC instead it would be an hour, tops.

    With a Supercharger I could drive full speed, stop for a quick lunch/bio break, and be on my way. That's not even taking into account the larger range of the Model S. Even if the pack lost some capacity over time, it would just increase my Supercharger time modestly.
     
  6. WhiteKnight

    WhiteKnight _____ P85 #549 _____ Sig Red / Sig White

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    Just to be crystal clear, though, what we are trying to discern is the RATIO between 55 mph and 75 mph. The 300 mile figure (at 55 mph) for the Model S is given to us by Tesla and it incorporates new battery cells, new drivetrain, new tires, etc.

    As VolkerP has illustrated with the Roadster graph from the spreadsheet, the major change in Wh/mile from 55 mph to 75 mph, comes from wind resistance/aerodynamics. The Model S has a much lower coefficient of drag than the Roadster (like ~0.22 vs ~0.34) BUT the Model S is also a much bigger car so the CdA (taking Area into account) could very well be equal.

    VolkerP did you get that CdA factoid from Tesla? I had not heard before that the increase in Area of the Model S Almost exactly offset the decrease in the coefficient of drag, even though it is easy to believe.
     
  7. VolkerP

    VolkerP EU Model S P-37

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    WhiteKnight,

    the CdA guesswork was in a TMC forum thread:
     
  8. WhiteKnight

    WhiteKnight _____ P85 #549 _____ Sig Red / Sig White

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    I am not down on the Model S, I like it a great deal and hope to buy one. BUT I realize if I buy the 40 kWh pack with a stated 160 miles range, I still can NOT drive from Atlanta to Birmingham, AL (146 miles on I-20). If I go 55 mph on I-20 I will die after being rear ended by a semi. If I drive 65 or 70 mph, I will run out of range. If there is a charger halfway, I can drive for 60 minutes, stop for 30 minutes, drive for 60 minutes, stop for 30 minutes. Not really the way I like to travel.

    Imagine if I wanted to go to Disney World in Orlando? That's not my idea of an enjoyable road trip even IF there are chargers along the way.

    Compare that with a BMW 535i which gets 31 mpg on highway and has an 18 gallon tank. You could drive 550 miles stop for 5 minutes to fill up and drive another 550 miles.

    The Deloitte study said something like 90%+ of Americans drive less than 50 miles per day and yet 90%+ of Americans want 300+ miles of range. The Model S promises 300 miles but does not deliver at highway speeds (when you really want the range). But that's okay because you are hardly ever going to need it anyway! Take the minivan to Grandma's house.
     
  9. Todd Burch

    Todd Burch Electron Pilot

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    WhiteKnight, I see what you're saying...I usually drive about 70-75 mph on the highway, like most people.

    However I realise that I'm making a compromise in one area (refueling speed) in order to get many benefits in other areas. With the superchargers, I still see the 85kWh pack as a road trip car. Yes, I'll have to drive a little slower (might take rural roads which typically have a speed limit around 55mph).

    Will it take me longer to get to my destination? Yes.
    Will I be forced to stop for about an hour every 3 hours? Yes.
    Is it still worth it to me for my relatively infrequent road trips? Yes.

    So this is really a very personal opinion that people need to formulate based on their own goals an experiences...
     
  10. WhiteKnight

    WhiteKnight _____ P85 #549 _____ Sig Red / Sig White

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    Okay, I promise not to be "that guy" that responds to every post, but this is a great example.

    Let's assume for argument's sake that Tesla decides that between Toronto and Montreal they need two Superchargers instead of one, because 542km / 336 miles needs two charge points approximately 180 km / 112 miles apart. So they locate one charger in Prescott, ON and another one in Belleville, ON (I've never been to Ontario but these look like good points on the map). So it's 112 miles from Prescott to Montreal and 112 miles from Belleville to Toronto.

    If I purchase the 160 mile pack I am only going to get 112 miles at 120 km / 75 mph. So I've got to drive slower than highway speeds just to have some range on either end of my journey for the local portion. And then I've got to stop at each Supercharger for the full 60 minutes or more (depending on the charge rate). So best case scenario is I start with 100% charge - drive 2 hours - stop for 1 hour - drive for 2 hours - stop for 1 hour - drive for 2 hours - and finally charge again for local range or arrive at my overnight destination. Total trip time 8 hours+ compared to an ICE car at 4.5 hours on one tank of gas with lots of room to spare. And by the way, within a few years I will not be able to even do this do to lost battery capacity (unless you want to turn on your flashing hazard lights and go like 80 km/50 mph).

    With a 60 kWh pack I could travel about 260 km / 160 miles at 120 km / 75 mph. So I can move at highway speeds between Superchargers BUT I cannot skip a Supercharger, I have to stop at every single one. If I want to drive at 55 mph then I should have just enough juice to skip one of the Superchargers but that is only when my pack is brand new. Once the pack is 6-9 years old I will have the bare minimum of capacity to make it between Superchargers while traveling at (near) highway speeds. So again, you're looking at a 6.5 - 7.5 hour journey compared to 4.5 in an ICE vehicle.

    With the 85 kWh pack you can skip one Supercharger location while maintaining 120 km / 75 mph highway speeds but you cannot make it the whole way without stopping at least once to charge. So at a bare minimum you are adding mandatory 30-45 minutes to your trip time. Once 6-9 years have elapsed you will have to hit every Supercharger along the way (a mandatory 60-90 minutes) or you can revert back to slower speeds in order to stretch out your range. With the 85 kWh pack though you've paid over $12,000 more than a comparably equipped BMW 535i which is every bit as fast and nice and gets over 550 miles in range and takes 5 minutes to recharge.

    You can see from this narrative that the 40 kWh packs are really not big enough to seriously consider for highway driving (other than your daily commute). The 60 kWh packs are big enough to start if you're willing to deal with with the hassle of frequent stops to recharge. The 85 kWh packs are the only ones that come close to supplying the freedom of the open road (and that unfortunately dissipates over time).

    I love the Model S for what it is (the best EV on the planet by far) but it is not the car you pick for a major road trip.
     
  11. bint2k

    bint2k Member

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    nice post whiteknight, totally makes me think twice about this car - I was still planning to keep my ICE car for road trips, but still....
     
  12. Doug_G

    Doug_G Lead Moderator

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    Sure. I will use my Model S for most of my road trips. Maybe once a year I might take a longer road trip through areas with little or no charging available; for that, there's a car rental place two minutes from my house, and they pick you up.
     
  13. Waverider

    Waverider Member

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    My thinking exactly WhiteKnight. This is the second biggest obstacle keeping me from putting a deposit right now. The first being it's about $20-30k more than I realistically should be paying for a car. The bells and whistles and the EV coolness just can't get this car over the line in my mind. I live out in the middle of the desert. The 160mile version would be perfect for my daily commute (maybe 15-20 miles round trip) but I'd be trapped in town if something were to happen to my other ICE car. Yes this scenario is very improbable, but it happened to me last Christmas when my primary car was in an accident and I had to rely on the second daily commuter for the road trip to the in-laws.
     
  14. daxz

    daxz Member

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    I've figured the CdA by taking the dimensions and images from web site and calculated how much area the silhouette took.
    W x H x percent area of silhouette x Cd = CdA
    77.3" x 56.5" x .81 x .225 = 5.53 Model S
    72.9" x 44.35" x .8 x .35 = 6.29 Roadster

    Then I calculated the formulas from the roadster efficiency and range spread sheet and used the CdA ratios above
    Wh/mile =
    (179.9*v^-1.002) Ancillary Wh/mi
    + (-0.0003* v^2+0.0936*v +51.871) Tires Wh/mi
    + (0.02899* v^2 ) Aero Wh/mi [roadster has .0309 *v^2]
    + (0.006 * v^2 + 0.1669*v+51.667) Drivetrain Wh/mi
    + (24 Wh/mi) RoadsterToSAdjustment Wh/mi (57Wh/mi for 85kWh pack = 300miles @ 55mph)

    This diving by pack size yields a mileage graph like:
    RangeCurves.png

    At 75 Mph range is
    40kWh= 114 miles
    60kWh= 171 miles
    85kWh= 243 or 225 miles -- the 85kWh pack was calculated 2 ways.
    Where the 55 miles = 300 miles and where the Ancillary+Tires+Drive Train curves had the same adjustment factor (+24w above Roadster) as the 40 & 60 kWh packs.

    For hypothetical trip of 340 miles 60kWh pack would need only 1 stop traveling at 70mph wasting .7 hours charging including 15 minutes to get get hooked up. You would need a charger at 190-210 mile mark though. The time you wait for long trips makes up for all the short 5+ minute detours to gas station currently.
     
  15. Alan

    Alan Member

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    #15 Alan, Dec 21, 2011
    Last edited: Dec 21, 2011
    I do about 90% of my driving in my Roadster and about 10% in my Audi for those times I need more seats or more range (I dont include my Lotus Esprit in this as I drive that just for fun).

    If I swapped the Roadster for a 40kwh / 160 mile Model S then I think that would cover about 95% of my driving needs (extra seats sorted) so I would still need a car for long distances / road trips. With the 85kwh / 300 mile version it would be OK for 99% of my driving needs. I am down to probably two or three times per year where I would would be delayed by the need to recharge on route. I think thats the level where I would not need a second car - a few times a year it would be cheaper to hire or borrow a car off a friend (swap for a few days).

    The point I am making is that electric cars have huge advantages (fun to drive, low running costs, low CO2 etc) but you have to consider whether they work as your only car. If you regularly drive close to the max range per day then you will be disappointed as you have chosen the wrong car for you. Look at it another way - lets say that twice a year you visit a friend who lives on a rural farm with no proper road and for this you need a 4 wheel drive off road vehicle. Does that mean you must only consider 4 wheel drive off road vehicles as your daily driver? Perhaps its better to have the perfect car 99% of the time and use/hire something else for 1% (which will then remind you what is so good about your Tesla). Getting too worried about a small number of road trips per year and you could end up driving the wrong car for 99% of the time.
     
  16. goyogi

    goyogi Member

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    That's the way I look at it too, Alan. I'll have zero problems finding someone to swap cars with when I need to haul some big items or go on a long road trip where the charging infrastructure isn't present yet. Anything longer than 3-4 hours I'll fly.
     
  17. dsm363

    dsm363 Roadster + Sig Model S

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    Me too. In Texas you basically can't leave the state without a 10 hour drive so really a 230 mile journey is the farthest I'd need to drive. I'll fly anywhere else.
     
  18. WhiteKnight

    WhiteKnight _____ P85 #549 _____ Sig Red / Sig White

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    I think you hit the nail on the head with your illustration. And I love the last line about driving the wrong car 99% of the time.

    In the process of writing this post, I've almost talked myself down from the 60 kWh pack to the 40 kWh because I realize now I won't be doing any inter-city driving in the Model S so why pay for range I'll never use? And you can get a 40kWh model that is identical to the 85 kWh in every respect except range and slightly slower 0-60 (again, I'm only drag racing 1% of the time and $20,000 would buy a lot of time at the track).
     
  19. Alan

    Alan Member

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    Sorry to steer you back towards 60kWh and spend $20K of your hard earned cash for you, but think again about the slightly slower 0 to 60.

    You almost never use a cars top speed so the 110mph vs 120mph difference between the 40 & 60kWh packs is no worry. Accelerating from 0 to 60 is something you do all the time and its far more fun doing it in a fast electric car than in a fast ICE car. So far even our government has not managed to make accelerating fast illegal.

    You will notice a difference between 0 to 60 in 6.5 vs 5.9 and that difference is something you will enjoy every time you use the car. I dont know if anyone has figures for say 50 to 80mph but that makes a lot of difference when it comes to overtaking so is something I would want to know about when choosing between the different models.
     
  20. Todd Burch

    Todd Burch Electron Pilot

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    In the US in most (all?) states you can get a ticket for exhibition of speed if you gun it from a stoplight, even if you're not racing anyone.
     

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