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Model 3 Roof Rack Options - Comparing Efficiencies

Discussion in 'Model 3' started by egaertner, Feb 16, 2019.

  1. egaertner

    egaertner Member

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    As winter arrived I was excited to strap a roof rack on my Model 3 and take it to the mountains. I quickly discovered little information out there about how it would impact the range. Given the long cold uphill drive and variable weather conditions, I was determined to find the highest efficiency setup and characterize it for route planning. I started with a stock TM3 LR AWD, keeping as many variables constant as possible, and did 20+ runs up and down the highway gathering data. I tested with both the SeaSucker Monkey Bars and Tesla's Roof Rack, with various configurations of snowboards, carriers, and fairings.

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    Additional pictures, charts, and raw data: Model 3 Roof Rack Options - Comparing Efficiencies

    TL;DR compared to stock TM3 LR AWD 18":
    • Tesla Roof Rack -- 1.6% range loss
    • Tesla Roof Rack + Yakima FatCat 6 Evo -- 17.3% to 19.6% range loss
    • SeaSucker Roof Rack + Thule 91725 Flat Top Ski Carrier -- 26.7% range loss
    • Aero Wheel Caps Removed -- 5.4% range loss
    Test Procedure
    1. Get on the highway going 70mph with autopilot engaged and reset the trip meter.
    2. Drive 6.5 miles south, gaining about 130 feet in elevation.
    3. Log the Wh/Mi, disable autopilot, and get off the highway
    4. Get back on the highway going north and do the same thing again. This time losing about 130 feet in elevation.
    5. Average the north and south results together.
    I avoided traffic during the trials to not skew the data and threw out any significant outliers due to road conditions. I tried to test when the wind was at a minimum but this seemed to be the most significant variable I couldn't completely control.

    Controlled Variables
    • 55-60°F outside temperature
    • Dry highway road, minimal wind
    • 70mph on autopilot
    • HVAC off
    • Radio @ 25% volume
    • Tires @ 42 psi cold
    Configurations Tested

    Results and Real World Impact
    At the end of the day I care about how much time I spend on the road. To that end I plugged the Wh/Mi figures for each config into ABetterRoutePlanner to see how they would impact the round trip driving time to my favorite ski resorts.

    Wh/Mi Δ / Range Δ / Time Δ

    1. No Aero Caps
    +5.7% / -5.4% / +7 minutes

    2. SeaSucker
    +36.4% / -26.7% / +44 minutes

    3. Tesla Rack + T-Slot
    +24.4% / -19.6% / +28 minutes

    4. Tesla Rack
    +23% / -18.7% / +26 minutes

    5. Tesla Rack + Fairing
    +21.0% / -17.3% / +24 minutes

    6. Tesla Rack Only
    +1.6% / -1.6% / +2 minutes

    Accuracy
    For each config I did two or three round trip trials. On average the trials within a config varied by 2.2%.

    Cabin Noise
    I measured cabin noise for each config using the iOS app Decibel X. The absolute values are probably not too accurate, but the deltas are somewhat interesting. The baseline measured 83dB.
    • Config 2 (SeaSucker) measured 84.5dB. Without the fairing the app measured lower but the sound was much more unpleasant. Likely due to the frequency of the noise and concentration at that frequency.
    • Configs 3 and 4 measured 86.5dB and 86.1dB respectively. Config 5 (fairing) measured 86.7dB and was actually more unpleasant due to a small gap between the fairing and the rack+boards.
    • Config 6 (Tesla Rack Only) measured 85.1dB but didn't sound too different from the baseline in practice.

    Speed Impact
    I repeated testing of Config 6 going 65mph instead of 70mph. The Wh/Mi decreased by 9.9%, causing the range to increase by 11.0%. No big surprises here, but always interesting to verify physics.
     
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  2. DFibRL8R

    DFibRL8R Active Member

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    Heck of a first post, welcome to TMC!
     
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  3. chrislayy

    chrislayy Member

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    Did the feet of the 46" Yakima fairing all touch the glass roof? I tried the 52" but I couldn't get the 2 outside ones to make contact with the roof.
     
  4. egaertner

    egaertner Member

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    Yea they did. I actually got the 40” first and it seemed too small, 46” seemed just right. Width wise at least, wish it was taller like my old Thule one was.
     
  5. chrislayy

    chrislayy Member

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    I have the same setup as you. I'm going to try the Thule 52" Airscreen and see if that sits flush.
     
  6. thelastdeadmouse

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    Thanks OP, I'm planning a very long road trip in late spring / early summer, seeing an efficiency test with just the roof rack is super useful to me. Any chance you have or know someone with a relatively small rooftop cargo box you could test as well? I need the extra storage for my trip (we're camping in the back of the car) at the moment we're planning to store a cargo box in the car for the long drive out west, then move it up to the roof once the longest leg is done.
     
  7. egaertner

    egaertner Member

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    I’ll be interested to hear how that works. I looked at that but it didn’t seem like it would be able to mount to Tesla’s aero bars.
     
  8. egaertner

    egaertner Member

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    I do have a small carbo box actually, haven't tried it yet, but probably can once ski season slows down. Not sure actually if the u-bolts on it are wide enough to get around the Tesla rails, may need some custom modification.
     
  9. Lunares

    Lunares Member

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    Thanks for the data!

    I wish I could run the Smart TSlot 2 for the fatcat but my skis would be banging on the glass if that was the case (it's only about 4-4.5" clearance and my bindings are 5"). Will make sure to budget at least 20% extra energy for the first time using the ski rack!

    Thanksfully to tahoe/mammoth and back from san diego there are plenty of superchargers.
     
  10. StealthP3D

    StealthP3D Active Member

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    Thanks for posting your results! I love it.

    Can you fit the two snowboards using config #4 base to base (stacked in the center)? I think that might be the most aerodynamic of all by a decent margin. Also, if there is a roof-top sport box that mounts with T-mounts and can fit two boards stacked inside the box, that might be even better.

    I'm looking for a small but long ski box for the Tesla rack system, anyone have any favorites?
     
  11. Lunares

    Lunares Member

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    Pretty much any ski box is going to be less aerodynamic than just the boards/skis, purely based on the frontal area presented.
     
  12. StealthP3D

    StealthP3D Active Member

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    Correct me if I'm wrong, but doesn't that imply the range hit from the Tesla rack (bare) can be compensated for simply by driving about 1.5 mph more slowly?
     
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  13. StealthP3D

    StealthP3D Active Member

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    I'm not sure that's true if the box is sized just large enough to fit the snowboards.

    For example, the fairing on a streamliner (salt flat racer) increases the frontal area but greatly decreases drag.
     
  14. thelastdeadmouse

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    Drag is based on a the frontal area x drag coefficient. A streamlined box is going to have a larger frontal area but a much smaller drag coefficient.
     
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  15. WATT TF

    WATT TF Member

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    Can you post more photos of your setups? :)
     
  16. Lunares

    Lunares Member

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    Drag coefficient of just snowboards or just skis isn't THAT high compared to a streamlined box. The frontal area increase more than makes it worse.
     
  17. StealthP3D

    StealthP3D Active Member

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    You might be surprised. Especially with dual, side by side snowboards with upturned tips. It's not the drag coefficients of the snowboards themselves, it's what it does to the drag coefficient of the entire system.
     
  18. schnieds

    schnieds Member

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    How hard are the different racks (the ones attached to the M3 roof) to take off & put on? I personally only want the racks on part of the year for snowboarding or longish road trips and want them gone the rest of the time.
     
  19. StealthP3D

    StealthP3D Active Member

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    I've watched a video of the Tesla Model 3 racks being installed. I've seen easier but any rack is small pain in the butt to put on/remove. I want the Tesla racks and would leave them on about 5 months/year. Currently, I just fold the split rear seat down and extend my skis through the trunk. When I find a suitable top-box, that's the part I'll be removing/installing multiple times/year.
     
  20. themapdoctor

    themapdoctor Member

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