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PrincessStela
Member
I can't get the 52" flush one side would always be up or the whole fairing needed to be warped... Tried 44" and that was too small. I'm guessing 48 is perfect. Will try it today if possible
Thank you for this thorough post! Very helpful and I’ll definitely be referring back to this in the future when I’m looking at configurations for my M3.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.
Additional pictures, charts, and raw data: Model 3 Roof Rack Options - Comparing Efficiencies
TL;DR compared to stock TM3 LR AWD 18":
Test Procedure
- 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
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.
- Get on the highway going 70mph with autopilot engaged and reset the trip meter.
- Drive 6.5 miles south, gaining about 130 feet in elevation.
- Log the Wh/Mi, disable autopilot, and get off the highway
- Get back on the highway going north and do the same thing again. This time losing about 130 feet in elevation.
- Average the north and south results together.
Controlled Variables
Configurations Tested
- 55-60°F outside temperature
- Dry highway road, minimal wind
- 70mph on autopilot
- HVAC off
- Radio @ 25% volume
- Tires @ 42 psi cold
- Baseline: Tesla Model 3 Dual Motor Long Range, 18” Wheels w/ Aero Wheel Caps
- Config 1: Aero Wheel Caps removed
- Config 2: SeaSucker Monkey Bars, Thule 91725 Flat Top Ski Carrier, 2 snowboards bindings down, Yakima Wildshield Fairing 46” [Picture]
- Config 3: Model 3 Roof Rack, Yakima FatCat 6 Evo T-Slot mounting, 2 snowboards bindings up (T-Slot mounts too low to put bindings down) [Picture]
- Config 4: Model 3 Roof Rack, Yakima FatCat 6 Evo standard mounting, 2 snowboards bindings down [Picture]
- Config 5: Model 3 Roof Rack, Yakima FatCat 6 Evo standard mounting, 2 snowboards bindings down, Yakima Wildshield Fairing 46”
- Config 6: Model 3 Roof Rack
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.
Legacystar
Member
I wish I had found this thread before I took my trip this last weekend. I spent a bunch of money to get the Tesla rack and some Yakima powder hound mounts. It took three snowboards about 300 miles from Seattle to Spokane, and my efficiency was atrocious. I have a performance model with 19 inch wheels, 245 width and a usually make it from my home in Renton to Moses lake with a few percent remaining (180 miles) On this trip I had to charge three times, averaging over 500wh/mi. The rack plus snowboards added about two and a half extra hours to my trip, I ended up putting the snowboards in the trunk with the back seat down and we made it home with only one charging stop. I'm wondering if a fairing in front of the snowboards would help, because not only do they cause drag, they cause lift which will increase the drag.
StealthP3D
Well-Known Member
A roof fairing for the ski rack is likely to increase drag but every situation can be unique. Generally, they are more for "looks" than actually helping to reduce drag. Did you have the three snowboards side-by-side or were two of them stacked base to base? The latter would cause considerably less drag than three abreast. Also, small changes in fore/aft mounting can have a relatively large effect on drag.
I've always used the split folding seats feature of my cars to carry my skis inside the cabin for not only this reason, even on my gas cars, but also, I've noticed it keeps the bases running fast and reduces the need to constantly hot wax. The fine grit in road grime becomes incorporated into your bases and it acts like brakes against the snow. Just as the increase in aero drag might require additional charging stops, the slower bases might be the difference between making it to the base of the lift on momentum or having to hop like a frog to get to the chair! Of course, the former is caused by aerodynamic drag and the latter by hydrodynamic drag.
One of the better ski cars I've had in my long skiing career (before I got the AWD Model 3) was an old Volvo 144 Grand Luxe. It only had RWD but I lucked upon a good deal on the most expensive trim level that came with the best rear differential for snow traction. That, combined with the light weight 4-cylinder engine, made the car a really good winter driver with balanced handling. It also returned very good MPG for those longer ski trips. The downside was it was a very slow car which was made even more apparent if I put skis on the roof. And my MPG would plummet. Ever since then I have avoided putting open skis/snowboards on the roof if I could help it. And that's when I noticed my base wax was not needing to be refreshed every long trip.
Since most energy on a highway trip is consumed simply over-coming air resistance, keeping a clean aero profile is super important to how much energy you need to get somewhere. Air resistance really is what creates almost all the work done by the motor. Did you know bicyclists could easily cruise at 80 mph if their bike had suitable gearing and there was no air resistance? That's why Tesla pays so much attention to ensuring their cars are aerodynamic, even their SUV's. And that's why I refuse to give up my Aero wheels! Aerodynamic efficiency matters in so many ways it boggles the mind:
1) Number of charging stops
2) Time spent charging
3) Cabin quietness. I love a serene ride.
4) Performance at higher speeds, like highway passing maneuvers.
5) longevity of battery and powertrain (battery life is directly proportional to the number and depth of battery cycles).
6) Cost of charging (or gasoline fill-ups).
People who think considering aerodynamics is a waste of time are simply ignorant as to how large an impact poor aero has on their comfort, convenience and cost of travel.
Legacystar
Member
i ran two of the boards together, and one in the upright position, my rack doesn't fit 3 across. i just pulled the numbers on tezlab, and it looks like on the same stretch i averaged 519wh/mi with the rack, and 355wh/mi without, so about a 31% loss. temp was in the low 30s which doesn't help, and i had 3 people and a totally packed car. $400 for tesla bars, $200 for the ski rack, and a 31% efficiency loss is hard to swallow, i may just stick with putting the seat down if i can't find a better solution.
Inside with the seats down is the best if you have the room, but it's easy to see why roof-mounts kill efficiency.
I wonder how a hitch mounted snowboard rack would fare in comparison - it probably depends on how high above the trunk the boards end up sitting. If you can keep the boards low enough that the bindings stay out of the wind, that would probably be best - I don't see that anyone makes a rack that lets you attach the boards low and horizontally so you can keep them out of the wind completely.
If you want to keep them on the roof, a roof-box that can hold all your boards would do better than just having the boards up there - but it still kills me that just about all the roof boxes out there are not designed with actual aerodynamics in mind, just designed to look aerodynamic - most would perform better mounted backwards! Tesla Model 3 with roof-rack box gets much better range if you flip box around
Only other thing to do is to slow down, depending on how fast you are driving, but that's not always possible, either.
StealthP3D
Well-Known Member
A hitch mount would perform terribly, not much better than roof mount aerodynamically, and would have the added huge disadvantage of being the grimiest place to mount your boards. Snow sports depend upon clean bases to reduce friction to a minimum. Mounting boards on a trailer hitch, without a weather-proof box, is a disaster from the standpoint of maintaining your bases. You can't just wipe the bases clean with a damp rag because the dirt becomes embedded in the pores of the wax and p-tex bases. Those pores are necessary to break the surface tension of the moisture in snow and provide good glide.
Aerodynamics are not very intuitive either. Just because the boards are "drafting" behind the vehicle does not mean they are not seriously disrupting the airflow. The rear of a vehicle is the most important from a standpoint of maintaining a low Cd. The good thing is it won't increase your effective frontal area like a roof rack does. But no serious skier or snowboarder wants to subject their boards to that kind of grime.
So I agree strongly that inside is, by far, the best place, if at all possible.
Not comparable to snow sports stuff, but I did a test with cruise control at 65mph on a long flat stretch of freeway and checking the energy display.
~270Wh/mi: base rack + boat rack + kayak
~250Wh/mi: base rack + boat rack (empty)
Have not done the test with the easily removable parts of the boat rack (which have the most frontal area and are not aerodynamic) removed, or with the base rack only, or with no rack. However, with the easily removable parts of the boat rack removed, it did seem to be around ~235-240Wh/mi, but that was on a different road with more variation in elevation and speed (traffic, speed limits), so cannot be too sure.
Base rack is Yakima BaseLine + CoreBar, not the one sold through Tesla (which is probably slightly better aerodynamically).
Legacystar
Member
Damn those rear wheels drives use nothing, that's still pretty low consumption! I roll around empty at over 300wh/mi
Not a snowboarder, but can you remove the bindings, then stack the 3 boards so that the rocker/camber all snug together? Having that open duckbill between the two boards doesn't look all that aero.
A fairing, with 3 boards across, with bindings down might work as well.
I have skis, with easily removable bindings. I've considered a roof rack, but I'd remove the bindings before putting them up there.
The rated efficiency line on the energy screen appears to be 227Wh/mi, though I do not know how exactly that compares to 65mph on cruise control on a flat road. The car is a RWD (the model that used to be called SR+) with 18" wheels, aero covers, and LFP battery.
Legacystar
Member
I could, but it's a lot of work to pull the bindings and install them again on the mountain.
Having used a trailer hitch mounted cargo rack with stuff strapped onto it on road trips at high speeds, I found that as long as whatever it is that you're stashing back there fits within the profile of the rear of the car (so the lowest point is above the rear valence and the highest point is below the trunk-lid and it doesn't stick out the sides), you don't notice any significant change in efficiency. The airflow behind the trunk is so turbulent, it doesn't change efficiency much.
That said, in wet/grimy road conditions, it would absolutely get super-dirty, so not a good place for skis / snowboards.
I still think that a properly designed, aerodynamic roof box would be a hit for EV owners.
StealthP3D
Well-Known Member
Hitch racks that I've seen for skis and snowboards definitely stick the boards above the trunk lid. And that's an arodynamic no-no.
Uhm, not sure you are interpreting DaveEV's comments correctly, or maybe I'm not. My understanding is that hitch-mounting is more efficient than car-top mounting, since the hitch-mount sits in a turbulent area already.
Yeah - hitch mounting has the potential to reduce drag compared to roof mounting, but it depends on the details - specifically how much of what you're mounting sticks out beyond the rear of the car. Because bikes are racked up sideways, there's potential for significant drag if the bike's wheels stick out beyond the bumper and the seat / handlebars stick up above the trunk.
Someone tried removing the wheels from the bike when hitch mounting and found that reduced the hit on efficiency, for example, because the wheels stuck out beyond the bumper and trunk.
The aero drag from a hitch mounting bikes on a Model Y will be less than a Model 3 and similarly when comparing a Model X to an S, for example, as well.
Has anyone mounted a Skiguard Box before? I have one from a prior vehicle, but it's heavy in general at 55 pounds vs the ABS boxes. I know that the M3 static weight is rated for more, but wondering if the weight of the box itself will cause more stress on the 4 mounting points?
Skiguard's site only shows this for '19+ but I have a 2018, which to my knowledge is not different than the 2019 model.
www.skiguard.com
Skiguard's site only shows this for '19+ but I have a 2018, which to my knowledge is not different than the 2019 model.
Skiguard 830 Touring
Low-profile and aerodynamic roof box. Perfect for for most small and medium sized cars. Comes in 2 versions: 830 Touring and 830 Sport.
www.skiguard.com
Mount it and let us know already! Also it appears many in this thread missed the guy that made a hitch Mount box for skis and basically had no efficiency hit.. very compelling to go the hitch route I’m just worried about the supercharger cables not reachingHas anyone mounted a Skiguard Box before? I have one from a prior vehicle, but it's heavy in general at 55 pounds vs the ABS boxes. I know that the M3 static weight is rated for more, but wondering if the weight of the box itself will cause more stress on the 4 mounting points?
Skiguard's site only shows this for '19+ but I have a 2018, which to my knowledge is not different than the 2019 model.
Skiguard 830 Touring
Low-profile and aerodynamic roof box. Perfect for for most small and medium sized cars. Comes in 2 versions: 830 Touring and 830 Sport.
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