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Efficiency with Trailer?

Discussion in 'Model X: Driving Dynamics' started by Jrogville, Feb 3, 2018.

  1. Jrogville

    Jrogville Member

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    High Springs, Florida
    I’m thinking about doing some towing with a 4x8x 4 ft high enclosed U-Haul trailer with about 500 lbs of cargo, but with the location of superchargers and where I need to go, it might be a close thing range-wise.

    To get from one supercharger to another, I need to drive 115 miles with the loaded trailer, then I can get rid of the cargo and trailer and drive another 50 miles to the nearest supercharger.

    I have a six-seat 90D. I figured I could push it and leave from the SC at 95%, which would give me about 235 miles of rated range. Getting to the next supercharger with 10% of battery capacity would mean a combined efficiency for the two segments, with and without trailer, of 80%. I don’t know if I get get up to 80% while pulling that trailer with 500 lbs.

    At 70 mph, I usually get about 85%. And at 55 to 60 mph, I can get about 90 to 95%.

    Does anybody have a feel for this, and whether I would be safe? I haven’t towed anything with my Midel X up to now, so I don’t have any experience to compare it to.

    My alternative is to use the GMC Yukon instead and then I don’t the trailer, but I don’t really like to drive it that much anymore, especially with a trip like this that would be about 360 miles in total, round trip. I would really appreciate any insights you could give me.
     
  2. Yinn

    Yinn Active Member

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    Those U-Hauls are the best with our car, I'd buy one if they would sell me one. The 4ft height will help a bunch with your efficiency. The aero is going to be the biggest factor, not so much with what you're towing if you're on the highway.

    As a comparison for my driving style, I usually get about 75% of rated range and I have a six seat 75D.

    - In the cold (~35 degrees) towing an open trailer with ~100lbs of load, I was using close to 900wh/mi to tow travelling about 60-75mph. This was an approximate range of 80miles.

    - In mild weather (~55 degrees) towing an enclosed v-nose trailer (4.5ft wide x 8ft long x 5.5ft tall) with ~2000lb load towing at 60-75 mph, I was only using about 500-600wh/mi for about 120-144 miles of actual range.

    Given you're in FL and you have an extra 20 miles of rated range (~15-17 mi actual) you should be ok , but I don't really understand your trip plan. What do you mean by this?

    If you only need max 115 miles between superchargers, you should be more than ok.
     
  3. Jrogville

    Jrogville Member

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    Thanks for the info, Yinn. What I meant is that of the total 165 miles between the superchargers, 115 miles would be with trailer and cargo, then I would drop off the cargo and return the trailer so that the remaining 50 miles would be with just the car.
     
  4. Yinn

    Yinn Active Member

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    Ah gotcha! So if you're getting about 85% your rated range; your consumption is most likely around 360wh/mi without a trailer. You will use about 60 rated miles to travel the last 50 miles.

    Assuming a 600wh/mi consumption...you would need a rated of 227 to travel the 115 actual miles with a trailer. Even if you got the rated wh/mi for the last 50 miles, you wouldn't be able to make it.

    If you can manage about 500wh/mi, you would be able to just make it. I've dipped into 400's before over the course of about 50 miles while towing, but that was travelling at 45mph with very little stopping.

    If it were me, I'd first see what the weather is like. If it's above 50, clear, sunny and minimal wind. I'd probably give it a go - especially since you have a High Amp Charger. I'd probably try to find a destination charger or other L2 charger as a backup to be safe. For the first 30-50 miles, I would probably drive as cautiously as possible to see what my wh/mi is and then play the rest by ear. If it's below 50, raining, or windy; I'd probably shelve the idea.
     
    • Like x 1
  5. ecarfan

    ecarfan Well-Known Member

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    #5 ecarfan, Feb 11, 2018
    Last edited: Feb 11, 2018
    When it comes to EV energy usage, speed is the primary factor, as you have already experienced.

    The trailer you describe is basically a box on wheels. It creates a lot of additional drag. Aerodynamic drag increases as the square of the velocity. Doubling the velocity quadruples the drag. This is why slowing down signficantly greatly increases energy efficiency.

    Without actually towing the trailer in question you cannot know with any precision what your energy usage in Wh/mi is going to be. Since the trailer is a rental you can’t run a test without renting it.

    The trip you describe, towing for 115 miles and then driving another 50 miles to a Supercharger, sounds problematic to me at freeway speeds. My guess, based on other towing threads on TMC and my own research in preparation to start towing a camper trailer with X100D later this month, is that towing that trailer at 65mph could use 800 Wh/mi or more. That is only a guess.

    Go slow.
     
    • Informative x 1
  6. BerTX

    BerTX Supporting Member

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    Also note that almost all ST trailer tires are rated for 65 mph. You have to really work at it to find some that are rated higher, and they cost more. U-haul also has a 65 mph limit on their trailers.

    So don't just slow down for range, slow down for safety.
     
    • Like x 1
  7. boelkers

    boelkers Member

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    Location:
    Minnesota
    Here is my biggest towing experience from last summer.
    Model X 75D - 5 seater
    16' Fiberglass boat - weight 900lbs dry - Boat cover on to improve aerodynamics
    Trailer weight - 500lbs, not sure on this but its all steel and heavy to move
    Myself and 1 passenger
    Additional 3-400lbs of gear weight divided between X and boat
    Total weight estimate with driver/passenger, gear, boat, trailer = 2000lbs

    We went on vacation and did a round trip of about 500 miles. It was July and temps were in the 70s. The first 225 miles I drove between 55-60 mph and my average was between 500 and 600 Wh/Mi (it being a year ago and didn't have Teslafi yet so I don't remember exact number). Used the AC the whole time. This was on the interstate and as we got closer to the supercharger I would speed up if I knew we would have plenty of charge to make it. The first supercharger was at the 100 mile mark. The 2nd was our lunch stop at 180 mile mark. Got a full charge here and the last leg of the trip was about 45 miles on 55mph roads. Spent a week at our spot and slowly charged using a standard 15amp outlet.

    Took a different route home thinking I could skip the 2nd supercharger from our trip up as it was a out of the way to get there. This could potentially take off 50 miles of the trip home. Drove 60mph for the first 50 miles and then determined I overestimated my Wh/mi usage so I bumped it up to the speed limits of 65 and 70 when appropriate. Made the 100 mile leg to the supercharger just fine. I remember having about 28% battery when we arrived. The downhills were nice. Next leg of the trip was 100 miles to home. Drove around 30 miles on interstate at 65mph and the last 70 miles were on a 55mph highway. Made it home just fine with around 20% battery I think.

    Not sure if any of this info will help you out but wanted to share in case it would.
     
    • Helpful x 1
    • Informative x 1

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