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Model X Travel Trailer Consumption Analysis

Discussion in 'Model X: Driving Dynamics' started by ohmman, Nov 4, 2016.

  1. ohmman

    ohmman Maximum Plaid Member

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    There has been discussion about energy consumption in a number of Model X towing threads (1). The real world information from these threads provides value to those who are considering purchasing, renting, or otherwise using a travel trailer. The data are extremely sparse right now, but at least some exploratory analysis can be attempted in order to get a feel for differences between the vehicles.

    We have @JimVandegriff towing a 22' Airstream Sport with an X 90D. A Safari Condo Alto R1723 is being towed with an X P90D by @fortytwo. And @jackbowers is towing a Bowlus Road Chief Lithium+ with his X P90D. I think the most valuable comparison is in flat conditions at about 55mph, as this is a reasonable towing speed and aids in controlling for the other variables.

    That data, as I've collected so far from their threads and the blog (2), looks something like this.
    Screen Shot 2016-11-04 at 1.31.16 PM.png

    Something looks awry here. Specifically, the numbers that I was able to glean from @fortytwo's blog posts are suspiciously high compared to their counterparts. This is especially confusing due to the aerodynamic nature of the teardrop, and the fact that it is the lowest weight vehicle in the list. If I missed something from their blog, please let me know. I used the FAQ as well as a couple of other posts, but there aren't a ton of data points in there, at least as far as I could find. I think it's possible that they were running heat, which would definitely skew the numbers out of their favor.

    The Bowlus looks terribly impressive at 475Wh/mi. Of course, it's also terribly expensive, costing more than the Model X itself. So budget may constrain many out of that option.

    Any other towing data for travel trailers would be a wonderful addition to this thread. I'm also interested in hearing from members with towing experience and/or aerodynamics expertise. I did get a rough number from @AnOutsider off-forum, which was that his high-wall popup, which is 3" higher than the X and 4" wider, square, and heavy, cuts range by about half. On his P90DL that would be something like 700Wh/mi, or (obviously) a 200% towing premium.

    Thanks also to @ecarfan who has been having this conversation in PM with me over the last few weeks.

    Notes:
    1. https://teslamotorsclub.com/tmc/threads/test-report-towing-the-bowlus-road-chief.68089, https://teslamotorsclub.com/tmc/threads/teslaxcanada-one-wild-idea.73395, https://teslamotorsclub.com/tmc/threads/initial-trailer-pulling-report-90d-and-airstream-22ft-bambi-sport.74540
    2. Promoting Sustainable Energy & Transportation
     
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  2. vandacca

    vandacca ReActive Member

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    @ohmman, do we know what wheels @fortytwo has on his X? If it's 22", that could explain the discrepancy.
     
  3. ecarfan

    ecarfan Well-Known Member

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    Good point. I searched the site at www.teslaxcanada.ca but could not find a reference to their wheel size. Looking at the photos of their X they do not look like 22" wheels to me.

    [​IMG]

    [​IMG]
     
  4. vandacca

    vandacca ReActive Member

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    #4 vandacca, Nov 4, 2016
    Last edited: Nov 4, 2016
    Yup, I agree - those look like 20". However, I remember reading of someone's trek with a trailer with 22" and they were planning to switch to 20". I wonder if it was @fortytwo? Initial data may have been with the 22"??? I'm probably grasping at straws as I can't find any references to @fortytwo's wheel size.
     
  5. ohmman

    ohmman Maximum Plaid Member

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    Technically, I tried to correct for wheel size in my unladen column. I may have messed that up, but I thought a P90DL with 22" wheels was supposed to get 250 miles rated. If so, that seems to equate to a 349.5Wh/mi rated consumption. My other assumption is that the rated consumption is about correct for 55mph. That's based on my experience with the S and X, both of which seem to actually do better than rated at those speeds. Happy to be nudged in the correct direction here if anyone has contradictory information.
     
  6. CmdrThor

    CmdrThor Active Member

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    I'm pretty sure the P90DL rated miles of 250 is with 20" wheels. 22" wheels take a 10-15% range hit according to the design studio.

    I've towed a travel trailer, but I was very rarely going 55mph flat. I think the only time we were going that slow I was going up a mountain and using 1720 Wh/mi.
     
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  7. ohmman

    ohmman Maximum Plaid Member

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    You're right. I assumed that 22" wheels were standard on the PXXD series but even in the P100D design, you have to select them with that caveat.

    I believe the only person towing with 22" wheels is @jackbowers. At least, he did for his test drive outside of Oxnard. That being the case, the Bowlus towing penalty drops even more than compared to the other trailers.

    I've reached out to @fortytwo off of TMC and will hopefully get some more data. I've been told they're pretty busy right now but hopefully can get me some more data at some point before long. I'll update once I have more information.
     
  8. ScottieLV

    ScottieLV Member

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    #8 ScottieLV, Nov 17, 2016
    Last edited: Nov 17, 2016
    I was referred to this thread by @fortytwo as I am about to place a deposit on a new Safari Alto 1723 with options weighing 1985 lbs without personal belongings. I was under the impression the less weight the more range you can get out of the Model X 90D with 20" wheels. You have shattered that idea.
    Would you be so kind as to do me a favor, if you have the time and inclination give me your thoughts on this travel trailer. I am considering a Lil Snoozy fiberglass Camper Trailer ([email protected]) with a dry weight of 2,650 lbs. It costs less, aerodynamic, is made in USA and has many other advantages I prefer. Height 7' 10.5" width 8' length 19'. Downside, it weighs more and I cannot park it in my garage.
    If your calculations are correct, I can tow a heavier trailer and get the same (or even better) range. Since I live in the desert, a white fiberglass trailer would be better than an aluminum trailer, less heat retention. Any thoughts would be appreciated as I was going to send Safari a deposit on 2016/11/18.
    Also, I sent a recommendation to Tesla that they should install drive-thru slots at all superchargers so we can charge without unhooking our travel trailer which is necessary in many locations. They responded with this Link to a YouTube video.
     
  9. ecarfan

    ecarfan Well-Known Member

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    Towing range with a Tesla is primarily about trailer aerodynamics, not trailer weight, except for when you are towing uphill or while accelerating (which obviously is a small percentage of all the time while towing).

    The Safari Condo Alto is 83"H (with roof retracted) x 83"W for a frontal area of 47 sq ft.

    The Snoozy is 94.5"H x 76"W (my estimate) for a frontal area of almost 50 sq ft.

    The Snoozy might look it has a more aerodynamic shape with the more pointed front end but the roof does not taper downwards toward the rear like the Alto so the Snoozy has a more squared off rear end which is less aerodynamic.

    The less aerodynamic body shape and the slightly greater frontal area tells me that the Snoozy will produce more drag than the Alto.. Plus it weighs over 25% more. It will use more energy when towing than the Alto.

    I placed an order for an Alto R-1723 model last week.
     
  10. ScottieLV

    ScottieLV Member

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    #10 ScottieLV, Nov 18, 2016
    Last edited: Nov 18, 2016
    Thank you for your reply. We do understand the increased drag with Snoozy and additional weight (which doesn't seem to make much difference, if I understand this correctly). We agree with your choice of the ALTO, I love the design and retractable roof with all those windows. I got these comments from one owner about the bathroom: "We did order the bigger bathroom/toilet (1723), but I would go with the small version (1713) next time. We only used it during the night and never showered in it anyway. We'd rather use the campground facilities". They also said to be aware of the dual fridge, it ate through our electricity like crazy so we had it replaced with a 12v that worked much better. They said A/C is a must, absolutely recommend it. Roof vent is amazing, the trailer gets quite hot in the sun. Personally, The Alto would go in our garage (our home owners association will not allow campers to be parked outside in our gated community) with some slight modificatons of the garage door height when open and that really appeals to us because the Las Vegas sun destroys things over time. No doubt is is a quality travel trailer. We are an old retired couple and here is why we are leaning toward the heavier Snoozy.
    1. No Holding tanks to deal with, toilet cassette makes it sanitary (see Video on this):
    2 White reflective all fiberglass with A/C mounted on rear not roof
    3 No propane 12v or 115v comes with optional semi-truck fridge
    4 Thick Queen mattress (customizable design) maybe you want two twin beds?
    5 Honda Generator Option (42" TV) We will stay in campgrounds 95% of time with electric and tv.
    6 Biggest concern is getting from one supercharger to next (range anxiety) driving 55mph, I would like to avoid destination chargers. Do you think 90% or 50% of time we can make it between Superchargers towing the Snoozy?
    7 We will have to park the trailer at our son's house (trade off, they get to use it)
    8 Looks like in most cases, to supercharge we will have to detach the travel trailer (at least the way SC are designed now)
    9 Please give me your thoughts about towing the Snoozy/Alto, if you dont mind, as we ponder this decision.
     
  11. ecarfan

    ecarfan Well-Known Member

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    Scottie, thanks for your comments. I did order the 12V electric-only fridge option for my Alto and also ordered the AC option. I appreciate that the R-1723 bathroom shower is cramped but the bathroom space is larger than the R-1713 model.

    Regarding towing the Snoozy vs. the Alto, as I explained in my earlier post, the Snoozy has a larger frontal area and a less aerodynamic shape overall so in my opinion those facts mean that the Snoozy trailer will produce more drag when towing resulting in a lower driving range than the Alto with the retractable roof. Without actual wind tunnel testing (which will never happen) or at least proper virtual modeling (which is beyond my capabilities) it is not possible in my opinion to accurately quantify the difference between the two trailers and come up with range numbers for each.

    The various threads on TMC about people towing trailers with a Tesla demonstrate that it is doable but you have to plan your trips carefully and if you are used to towing with an ICE you have to "adjust your attitude" about towing: travel at a lower speed and accept the fact that you cannot go as far per day. I am envisioning a scenario where I start out fully charged in the morning, drive for 3 hours or so at 50-55mph, stop at a Supercharger for lunch and charge, then drive another 2 to 3 hours and stop for the day at my destination for the night or for several nights. So I could potentially cover up to 300 miles/day unless there was a lot of uphill or headwinds.

    That would work for me. However I cannot see doing what you mentioned which was "avoid destination chargers". Superchargers are generally not that plentiful for those using their Tesla to tow because of the greatly decreased range, as the Supercharger network layout was designed for Tesla vehicles based on their EPA rated ranges . Some of the trips I am envisioning I can foresee not needing destination charging for several days since I can power my Alto using solar panels on the roof and LiFeP batteries as @fortytwo installed. But on other trips I will want to charge my Tesla overnight or over several days using the campground power supply.

    If the Snoozy meets your needs better that's fine, there is no question that you will be able to tow it with a Model X. Get the 90 or 100 though, the smaller batteries will be too limiting. I think that towing the Alto will provide a significantly greater driving range. Also, I am planning on towing my Alto with a Model 3, making it even more critical for me to have a trailer that offers the lowest possible drag while at the same time meeting my personal requirements for size and capabilities. The Alto's retractable roof and overall shape make it the best choice for me.
     
  12. ScottieLV

    ScottieLV Member

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    Wow, did you notice you beat me here by 2 months. Really am learning from your comments as we have much in common.

    I do understand & appreciate why the ALTO meets your needs & I also am impressed with their quality of build.

    When I was talking about destination charging I was refering to hotels. To charge at a hotel would mean ditching the trailer to get to the charger and then where would you ditch it? We plan to travel from campground to campground, choosing campgrounds along the supercharger routes for the most part. We would agree with your travel scenario completely. I would be apprehensive when crossing the Rockies on I-70 pulling the heavy honking Snoozy. We drove our MS to Chicago and back from LV and had a wonderful trip, staying in hotels & motels across the I-70 two summers ago & yes we have ordered a X90D with range of 257 miles to pull the T Trailer.

    I guess what I would like to hear you say is: In most cases I think you could make it from SC to SC or to campground DC provided you drive 50 to 55 mph. This means do not travel into a headwind or travel uphill (LOL). I also rationalize with the fact Tesla's SC network will grow over the next two years. I can see towing to New England and South Florida and up the West Coast to Vancouver, BC.

    FYI we have 35 ea 295 w panels on our south facing home roof, and always look for ways to save energy. Just our DNA I guess.
     
  13. ecarfan

    ecarfan Well-Known Member

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    I agree that if you are going from campground to campground you don't want to have to stop and do slow AC charging anywhere if you can avoid it. Yes you can unhitch the trailer, leave it in the parking lot, and plug in to a Tesla Destination charging station at a hotel but you will be there for hours and typically destinations like hotels or others reserve their chargers for paying guests not people passing through. It makes no sense to slow AC charge if you are not staying at that "destination".
    Sounds like a good plan.
    Given the near infinite number of possible travel routes in the US and the variable geography, I can't make such a statement. Again, careful route planning is critical when towing because EV range is cut in half, at least. But based on multiple threads on TMC by Tesla owners towing trailers, it is certainly doable.

    I've said it before, but to reiterate: I have never owned a trailer and have zero RV camping experience. I am basing my opinions on information posted by others and by my own analysis of the available data. For how I plan to use a camping trailer, the Alto seems like the best choice. It certainly is not the best choice for everyone. I do not plan to make weeks long trips moving frequently from campground to campground and covering a thousand miles or more during a trip. My expectation is that I will make an all day drive to get into the Sierras and then camp for several days at a time in one place, or maybe drive for two days in a row and then camp for several days in one place before returning home.

    We have kind of veered off from the thread topic of analyzing energy consumption while towing with an EV and gotten more into the feasibility of towing at all with an EV and route planning. My apologies.
     
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  14. siucity

    siucity Button Pusher

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  15. ecarfan

    ecarfan Well-Known Member

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    For sure. Looks like a typo. Should be "Wh" not kWh". I searched through Home - Bowlus Road Chief but cannot find the battery specs.
     
  16. ohmman

    ohmman Maximum Plaid Member

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    #16 ohmman, Dec 1, 2016
    Last edited: Dec 1, 2016
    Some additional data that I've backed out of @JimVandegriff and @jackbowers reports.

    Jack reported on a number of occasions that he uses about "12 additional miles of range" per thousand feet elevation gain. In his P90D, that equates to about 12 miles * 340 Wh/mi = 4080Wh of additional energy to pull the Bowlus uphill. However, his most recent pull over Donner Pass appears to have consumed more than that. I'm hoping for some more details on that drive.

    Jim at one point reported using 706 Wh/mi to go 40 miles at 55mph with a 1000' elevation gain. Considering his average of about 575Wh/mi on flat land at the same speed, that means he consumed approximately 5240Wh of additional energy to pull his Airstream Sport. There is limited other good, isolated data in his thread, but this appears to be reasonably close to his other reports.

    Considering the Airstream is up to 4500 lbs fully loaded (though surely quite a bit lighter), and the Bowlus is 2200 lbs dry (and probably not much heavier, considering how empty it looked when I met with Jack prior to his drive), I'm unsure how to reconcile that there's not a greater difference between these numbers, other than to say the data are too sparse to make much of a conclusion.

    Either way, there they are for reference.

    **Just for fun, I ran some numbers to see if Jim could pull his Airstream over Donner Pass, assuming all things equal and the numbers I've given above have any merit. The pencil/paper calculation looks something like this: Supercharger Rocklin at 318 feet. Donner Pass at approximated 7209 feet. [5240Wh/1000ft elevation * (7209 - 318) elevation gain] + [575Wh/mi * 68.3 miles to the peak] = 75381Wh. From that point, it's all regen for the remaining 9 miles to the Truckee Supercharger. Hey, that's interesting. :)
     
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  17. ohmman

    ohmman Maximum Plaid Member

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    After a good deal of research, I think it's time to update this thread regarding the consumption analysis. I have been working with @ecarfan privately on understanding travel trailer aerodynamics. Over the last month and a half, we've learned quite a bit about the topic. I'll preface by saying that I'm unable to provide real-world calculations, and I'm open to being incorrect about some of this. If there's something you can refute, I welcome the critique. Much of this comes from literature available online, and discussing with people are are familiar with the topic.

    One of the goals of good aerodynamic design is to keep the boundary layer - the air flowing over the surface - attached to the vehicle/structure at all times. Separation between the boundary layer and the surface creates low pressure and starts to suck air inward. So long as the design minimizes separation, the designer has control over the airflow as the vehicle moves through the air space. Another important factor is that air is generally not calm. Crosswinds can impact trailer dynamics and drag as well.

    I have learned that radiused edges, not only on the front and rear, but also on the sides, make a big difference to the Cd. Note this diagram, which I have also posted in the other trailer thread:
    [​IMG]
    In this regard, Airstream has had it right for a while, and Bowlus takes it closer to the ideal. But what of the Alto, with its teardrop shape?

    Teardrops are aerodynamic, but only if they have a relatively long tapered tail. Think about the Bowlus for a visual. They should taper inward as well as downward. The problem with most teardrop designs is that they're hard sided (no radius edges) and they drop off too quickly. What happens when a teardrop begins to slope down rapidly is that the boundary layer separates from the roof, creating low pressure in that area. Air from the sides of the trailer are sucked into this section, and since the edges aren't radiused, they create vortexes as they come over the lip. In the words of one person who analyzed the Alto design, "The smaller trailer is an aero disaster, with flat sides leading to the quick slope of the rear 1/4, it is certainly creating a monstrous pair of twin trailing tornadoes that might as well be drag chutes."

    Another voice of support for this claim was an individual at Can-Am RV, who confirmed that the fixed roof Alto (non-teardrop) has better efficiency than the retractable roof Alto. The "Altoistes" Facebook page apparently had some anecdotal support for this as well, but it wasn't terribly convincing.

    I hope to know more when @fortytwo hits the road again, but I do believe we've found one reason that the consumption numbers in my original post defied intuition. Our intuition about the aerodynamic qualities of a teardrop is incorrect.

    I wanted to post this to ensure that owners who are shopping for a travel trailer have considered this unintuitive outcome.
     
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  18. ohmman

    ohmman Maximum Plaid Member

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    This informative document was shared with me on the Airstream Forums in response to some questions about the Model X -- travel trailer linkage distance. It includes much more information that is applicable to our topic, and I found it fascinating.

    Regarding the linkage question, the yaw angle (angle of air travel across the roadway) changes the coefficient of drag significantly. This situation is exacerbated by hard edges on the trailer and by the tow vehicle-trailer gap. See the following diagram (apologies about the resolution) for the effects at yaw angles up to 20° (source: Hammache, Michaelian, Browand). This provides support for radius edges like on the Airstream and also minimization of the gap between the tow vehicle and travel trailer.
    Screen Shot 2017-01-06 at 7.33.21 AM.png
     
  19. AndreyATC

    AndreyATC Member

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    @ohmman
    Thank you for all the analysis
    Great thread!
    I hope we see more data as it gets warmer

    P.S. Quite surprised with Alto consumption. I was expecting better numbers for such light weight trailer and supposedly aerodynamic
     
  20. Laserbrain

    Laserbrain Member

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    More data about towing with a Model X:

     
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