120 mile experiment: To Aero or not?

tencate

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#1
aeroornot-png.10931

I did a little 120 mile experiment to answer a long standing question I have: Do the Aero wheel covers matter for the kind of driving I mostly do? So, on a hot lazy afternoon here in the desert Southwest, I did an experiment testing that out. I figure the results are worth sharing.

Weather? A hot, lazy afternoon, temperatures ranged from 86-88 degrees F during the entire driving experiment. Winds were light, about 10 mph, with occasional puffs up to 20 mph. Relative humidity was like 5% or so. Car had been driven around doing errands before the testing, the tire pressures----cold = 42 psi---during the test yesterday were 46 psi (plus or minus 1). The car's state of charge/range read around 220 miles and I ended at 150 or so.

I drove the exact same 29.9 mile loop 4 times. Nice music, an occasional deer or three, mountains of course, and the skies were pretty. :) The odometer matched exactly on all 4 loops. First loop was with Aero caps ON, next with Aero caps OFF. Took a brief restroom break and then took the 3rd loop with Aero caps ON, then finished the 4th loop with them OFF. The route consisted of parts of NM-4, I met very few cars during the experiment; I basically had the road all to myself. The speed limits range from 55 mph over one long stretch, to another 50 mph long stretch elsewhere and mountainous driving elsewhere. The remaining parts of the loop consists of sorta residential driving, from 25-35 mph. I used the cruise control to maintain my speed consistently during the whole trip and I didn't touch the climate control the whole time either. I had climate set to manual, and at a fixed fan speed to stay comfortable. Never messed with it during the whole trip. Altitude variation is from 6500 to 7500 ft. I reset the "trip" odometer just before starting the trip each time and recorded the results exactly the same upon my return to start.

Results:
Loop 1, Aeros ON, 185 Wh/mi
Loop 2, Aeros OFF, 187 Wh/mi
short break
Loop 3, Aeros ON, 180 Wh/mi
Loop 4, Aeros OFF, 181 Wh/mi

Conclusion. For my kind of driving, Aeros ON vs Aeros OFF doesn't seem to matter. Some day I'll try an experiment at highway speeds (75 mph).
Observation. I THINK that the ride was quieter with the Aeros ON by the way. I swear some of the wind noise was gone with Aeros ON. But that's subjective, just my humble opinion.
 

Dr. J

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#2
Does higher humidity cause higher (wind) resistance? Your dry, thin air is enviable, but sadly not representative of my part of the world. :( I would guess the aero covers make a bigger difference at higher speeds, higher humidity and lower altitude. I appreciate your tests!
 

tencate

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#3
Probably does matter! Not much oxygen up here either; ICE cars lose horsepower but are also more fuel efficient at this altitude as well. Someone should repeat the test at sea level, with moist and denser air. I suspect higher altitude is why I get good range efficiency here. But, I'm dying to try a test at real Interstate Highway speeds now.
 
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Dogwhistle

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#4
Hot day, high altitude, low humidity = high “density” altitude. The test atmosphere was pretty thin, if aero makes a difference, it would be least noticeable in those conditions!
 

tencate

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#5
Oh, agreed to be sure. But for those of us living at least a mile above sea level (Denver, Boulder CO Albuquerque, Santa Fe NM, Payson AZ, etc.) these conditions are pretty normal for summer (and forest fires) :(. That does however mean I'll only probably pop on my Aero covers for long trips. I kinda like being able to swap back and forth between the Aero look and the "Under" look; the "Under" look is especially nice with the chrome lug nuts IMHO. Nice to know that at least where I live I don't take any measurable efficiency hit for removing the Aeros. ;)
 

garsh

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#6
Very useful, especially about the noise level difference.

This seems to help confirm that the Aero covers don't help efficiency until faster highway speeds. I look forward to some test results at higher highway speeds.
 

JoeT

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#7
QUOTE="tencate, post: 118794, member: 12668"] View attachment 10931
I did a little 120 mile experiment to answer a long standing question I have: Do the Aero wheel covers matter for the kind of driving I mostly do? So, on a hot lazy afternoon here in the desert Southwest, I did an experiment testing that out. I figure the results are worth sharing.

Weather? A hot, lazy afternoon, temperatures ranged from 86-88 degrees F during the entire driving experiment. Winds were light, about 10 mph, with occasional puffs up to 20 mph. Relative humidity was like 5% or so. Car had been driven around doing errands before the testing, the tire pressures----cold = 42 psi---during the test yesterday were 46 psi (plus or minus 1). The car's state of charge/range read around 220 miles and I ended at 150 or so.

I drove the exact same 29.9 mile loop 4 times. Nice music, an occasional deer or three, mountains of course, and the skies were pretty. :) The odometer matched exactly on all 4 loops. First loop was with Aero caps ON, next with Aero caps OFF. Took a brief restroom break and then took the 3rd loop with Aero caps ON, then finished the 4th loop with them OFF. The route consisted of parts of NM-4, I met very few cars during the experiment; I basically had the road all to myself. The speed limits range from 55 mph over one long stretch, to another 50 mph long stretch elsewhere and mountainous driving elsewhere. The remaining parts of the loop consists of sorta residential driving, from 25-35 mph. I used the cruise control to maintain my speed consistently during the whole trip and I didn't touch the climate control the whole time either. I had climate set to manual, and at a fixed fan speed to stay comfortable. Never messed with it during the whole trip. Altitude variation is from 6500 to 7500 ft. I reset the "trip" odometer just before starting the trip each time and recorded the results exactly the same upon my return to start.

Results:
Loop 1, Aeros ON, 185 Wh/mi
Loop 2, Aeros OFF, 187 Wh/mi
short break
Loop 3, Aeros ON, 180 Wh/mi
Loop 4, Aeros OFF, 181 Wh/mi

Conclusion. For my kind of driving, Aeros ON vs Aeros OFF doesn't seem to matter. Some day I'll try an experiment at highway speeds (75 mph).
Observation. I THINK that the ride was quieter with the Aeros ON by the way. I swear some of the wind noise was gone with Aeros ON. But that's subjective, just my humble opinion.[/QUOTE]
 

JoeT

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#8
Thanks for this. We are picking ours up on Friday. We will set out immediately from the DC on an extended road trip. Worth knowing your perceptions about noise since we will be in the car for hours at a time. Not much at keeping stats but maybe I’ll give it a try. I’ll be pretty busy learning.
 

Frank99

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#9
Great test, tencate.

Your results match mine ( https://forums.tesla.com/forum/forums/new-aero-wheel-efficiency-data ). I did my 160 miles at 75 MPH, so should be some good data for those asking for highway results. The one variable that I couldn't control on mine was traffic - it was light, but on each run there was a spot or two where I had to slow down momentarily. But the numbers are close enough together to suggest that the aero wheel covers don't do much (if anything) to improve range.
 

tencate

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#10
Great minds think alike. Cool! :) All the truck data I can find on similar truck aero wheels (sometimes fabric) suggests somewhere between 0.5% to 1% per wheel savings. There's even a standard Jxxxx test for it that the aero wheel manufacturers quote in their sales spiel, likely wind tunnel. I did a fair bit of (internet) reading on these and it seems the cost savings for a long haul trucker might be from a few hundred bucks to almost $1k over a year. So, to me, using aero wheel covers is kinda like indexing spark plugs on an ICE. It probably does matter and is measurable but barely.

I'm driving to ABQ in a few days (100 miles one way), I may try the drive down without and the drive back WITH and see if the wind noise changes. It'll be qualitative of course but I'll listen carefully. I am an acoustics guy after all. ;) If I think it's noticeable and perhaps measurable, I'll write everyone back.
 

PNWmisty

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#11
Does higher humidity cause higher (wind) resistance? Your dry, thin air is enviable, but sadly not representative of my part of the world. :( I would guess the aero covers make a bigger difference at higher speeds, higher humidity and lower altitude. I appreciate your tests!
That test could not have been more favorable to reducing the measurable benefit of aero wheels. The high temperatures, high altitudes, low humidity and slow speeds pretty much insured the difference would be small. Of course if that's the only conditions the OP drives in, then it's probably valid for his purposes.

I do a lot of driving under 1000 foot altitude in much colder temperatures at much higher humidities and at higher speeds. There is a huge difference in wind resistance at 25mph to 50mph vs. cruising down the highway at 70-75mph. So I would expect a much larger difference between Aero and bare wheels in my usage.
 

tencate

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#12
I do a lot of driving under 1000 foot altitude in much colder temperatures at much higher humidities and at higher speeds. There is a huge difference in wind resistance at 25mph to 50mph vs. cruising down the highway at 70-75mph. So I would expect a much larger difference between Aero and bare wheels in my usage.
So, time for an experiment? I see from your signature that your car is a clone of mine, any chance you could find time to do something like Frank99 did? Sounds like where you live is the perfect place for it! :)
 

PNWmisty

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#13
So, time for an experiment? I see from your signature that your car is a clone of mine, any chance you could find time to do something like Frank99 did? Sounds like where you live is the perfect place for it! :)
The closest place I have for a test at 70 mph would be I-5 which is problematic with all the traffic. At those speeds even following another car at 5-6 lengths could be problematic in terms of drafting and comparing runs. Also, the test needs to be done without traffic aware cruise control. Plus, it's summer here now (too warm).
 

JimmT

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#14
I just finished my own experiment. For the first 1,500 miles that I had the car, I drove it without the aero caps on and averaged 243 Wh/mi. Then I put the Aero caps and drove for another 1,500 miles and my average Wh/mi is 224.

I'm not sure how much the Aero caps contributed to the better efficiency or if my driving got more efficient with experience. I'm going back to no Aero caps again :)