Any Model 3 RWD 18" driver willing to head to the Springfield MO area for data gathering vs. an AWD?

KarenRei

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#1
Thanks to a generous offer from [FONT=Roboto]@efusco[/FONT] @ TMC, we've got someone with an AWD 18" who's willing to gather data to let us compare the efficiency of an AWD and an RWD Model 3 in the exact same conditions. Obviously, for this we need someone with an RWD that's also running on 18" wheels who can get to the Springfield area (specifically, they're in Nixa). The test would be:

* Inflate tires to the same pressure (hopefully they have similar levels of tread wear!)
* Charge to similar levels (not a big deal)
* Have the same amount of driver / cargo weight
* Have the same climate control settings.
* Don't do it on a cold day where energy might be being diverted to pack heating

* Head to a flat area with little traffic
* Drive the same road at the same time (but far enough apart so as not to draft) at a constant speed. Measure consumption (should only take a couple miles).
* Do the same in the opposite direction, to cancel out any minor wind/slopes
* Repeat for different speeds (such as 55, 65, 75 and 85mph).


This will answer once and for all whether the EPA efficiency differences are as big as they let on in the real world, or whether they're due to different testing configurations (such as different wheels or whatnot). :) Bonus points: also do a rolldown test (in each direction) so that we can tease out any differences in rolling or aero drag.

Any takers?
 
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jsmay311

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#2
Any luck getting a volunteer?

I had tagged this thread to watch it in hopes someone would volunteer. It’s too far away for me, and I was hoping this effort would supersede my plans for doing something similar. Doing highway testing at various speeds in small-ish town Missouri would probably be quite a bit easier than in suburban Chicago anyway.

Still, I might have a chance to do some testing tonight if I can convince my brother to participate.
 

KarenRei

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#3
Nope, no volunteers :( I keep trying to find people to do the test, but no luck. I hope you get a chance to do yours!
 

jsmay311

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Nope, no volunteers :( I keep trying to find people to do the test, but no luck. I hope you get a chance to do yours!
Well, I tried. I had my RWD and my brother's AWD+P with the same 18" wheels with aero covers, same tire pressures, similar tire treads, and similar on-board weights. But there was just too much traffic on the local expressways to get high quality results. (And, like a dimwit, I left the A/C on during one of the four legs that we drove. :oops:)

Of the three remaining usable legs, only one was able to be done at constant speed with no slow downs or closely trailing vehicles in front (and risking drafting effects).

Leg 1: Unusable due to A/C use in the RWD. (Over 5.2 miles at 60mph, the RWD efficiency was 7.8% worse than the AWD, which is what tipped us off.)

Leg 2: Steady 70mph (no traffic issues). Negligible drafting effects (long following distances). Slightly downhill (dropped ~95 ft over ~6.2 miles).
RWD: 208 Wh/mi. AWD: 225 Wh/mi.

Leg 3: This leg was intended to be the reverse of Leg 2, also at 70mph, but traffic led to variable and unmatched speeds between the 2 vehicles. Speeds fluctuated between 55mph and 70mph, and we probably averaged about 65mph. There were also probably some uneven drafting effects from the surrounding vehicles.
RWD: 228 Wh/mi. AWD: 238 Wh/mi.

Leg 4: This leg attempted to keep a steady 60mph, and we managed to stay pretty close to that, but again there were some speed fluctuations due to traffic. But the fluctuations on this leg were pretty minor. The distance was 5.2 miles, and there were some elevation changes, but no significant net elevation change from the beginning to the end.
RWD: 184 Wh/mi. AWD: 189 Wh/mi.


So the highest-quality leg (one-way only) showed AWD energy consumption 8% higher at 70mph. But the 2nd-highest-quality leg had it only 2.7% higher at 60mph.

So long story short, I would still strongly encourage someone else who lives in an area with less traffic to do a much better job than this and get some more reliable data. :)
 

KarenRei

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#5
Hey, that's a start! As you note, not the best quality data, but still very interesting.

The EPA difference breakdown is:
  • City: 136 vs. 120 MPGe = 13,3% difference
  • Combined: 130 vs. 116 MPGe = 12,1% difference
  • Highway: 123 vs. 112 MPGe = 9,8% difference
But yours, as you note, were:
  • 208 vs. 225 Wh/mi = 8,1% (70mph, slightly downhill)
  • 228 vs. 238 Wh/mi = 4,3% (55-70mph, slightly uphill, poor quality)
  • 184 vs. 189 Wh/mi = 2,7% (60mph)
This strongly suggests to me that energy consumption differences are not as strong as the EPA stickers suggest (supporting for example the hypothesis that they might have done that testing with a different wheel config). But you're right, we really need more / better quality data to conclude that. But it's encouraging!

Maybe if we're lucky someone else will redo the testing in better circumstances, and maybe add in some rolldown tests :)
 
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PNWmisty

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This strongly suggests to me that energy consumption differences are not as strong as the EPA stickers suggest (supporting for example the hypothesis that they might have done that testing with a different wheel config).
If Autopilot was not used, then the biggest variable here is probably the drivers. How they hold their foot on the accelerator to moderate speed could cause HUGE variations in efficiency. I would suggest, for the results to have ANY meaning beyond the EPA figures, both cars should use Autopilot 100% of the test (with the same software version), the distance covered should be at least 30 miles/leg, there should be at least 3 legs of different conditions and there should not be any other traffic that interferes with the AP maintaining set speed.

Also, there should probably be at least 3 RWD and 3 AWD vehicles. Due to motor binning, it would be nice if there were 3 Performance AWD thrown in also. With 3 vehicles of each type, we would get an idea how much of the variation is due to the different configuration and how much is due to other factors.

If the same driver was used for each of the three runs already recorded, I have zero faith the results are meaningful in the way you have interpreted (that the EPA figures exaggerate the differences).
 
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#8
I dont believe drivers make a big difference in efficiency for an EV as they start and stop at roughly the same time, same route, same aero drag. As long as their pedal position doesnt cause to engage regen more than the other minor differences in speed are averaged out over distance. The numbers above are informative.

Keep in mind that EV motors have a mich wider throttle range for high efficiency as a gas vehicle (where driver pedal position matters more).
 

PNWmisty

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I dont believe drivers make a big difference in efficiency for an EV as they start and stop at roughly the same time, same route, same aero drag. As long as their pedal position doesnt cause to engage regen more than the other minor differences in speed are averaged out over distance. The numbers above are informative.

Keep in mind that EV motors have a much wider throttle range for high efficiency as a gas vehicle (where driver pedal position matters more).
I understand the relatively flat efficiency curve of electric motors. But I've observed EV drivers going into regen while trying to basically cruise at a constant speed. And since any resistance applied by regen is only around 50% efficient, it can totally throw the results.
 

KarenRei

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I understand the relatively flat efficiency curve of electric motors. But I've observed EV drivers going into regen while trying to basically cruise at a constant speed. And since any resistance applied by regen is only around 50% efficient, it can totally throw the results.
So long as the vehicle parameters (esp. v and dv, which cruise control maintains) are the same, both vehicles should regen at the same times.
 

PNWmisty

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#13
So long as the vehicle parameters (esp. v and dv, which cruise control maintains) are the same, both vehicles should regen at the same times.
I was speaking specifically to vehicles using human controlled throttle inputs. And that is why I recommended any such tests be done with Autopilot (or at least TACC). If TACC is used, there can still be very significant variation in power consumed due to varying amounts of regen used if the test is done with other vehicles in the same lane. Even the act of one car using TACC, which is following the second car using TACC, could cause one of the cars to apply significantly different amounts of regen.

Which brings up a subject I am curious about. I would like to know how a string of various Teslas, all following one another, would behave if they all had TACC activated and the lead vehicle had their TACC set a couple of mph slower than the cars following the lead car. I'm wondering if, under certain conditions, a "slinky" effect might set up. Sometimes, a string of cars in a line, all driven by humans, will develop an oscillation that manifests in the last car having to constantly speed up and slow down to maintain following distance with the car it is following. This is at the root of "stop and go" traffic jams. On a related note, what would the traffic patterns and movements of an entire freeway full of Teslas at rush hour (with no non-Teslas) look like if they all had TACC activated? Would "stop and go" conditions develop in a freeway populated entirely by TACC operated vehicles?

There are probably enough Teslas in California now, with the successful launch of the Model 3, that an event could be set up somewhere between LA and SF with a hundred or more Tesla's driving in a large pack. Maybe the organizer could coordinate the pack if everyone tuned to the same webcast.
 

MelindaV

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#14
I was speaking specifically to vehicles using human controlled throttle inputs. And that is why I recommended any such tests be done with Autopilot (or at least TACC). If TACC is used, there can still be very significant variation in power consumed due to varying amounts of regen used if the test is done with other vehicles in the same lane. Even the act of one car using TACC, which is following the second car using TACC, could cause one of the cars to apply significantly different amounts of regen.

Which brings up a subject I am curious about. I would like to know how a string of various Teslas, all following one another, would behave if they all had TACC activated and the lead vehicle had their TACC set a couple of mph slower than the cars following the lead car. I'm wondering if, under certain conditions, a "slinky" effect might set up. Sometimes, a string of cars in a line, all driven by humans, will develop an oscillation that manifests in the last car having to constantly speed up and slow down to maintain following distance with the car it is following. This is at the root of "stop and go" traffic jams. On a related note, what would the traffic patterns and movements of an entire freeway full of Teslas at rush hour (with no non-Teslas) look like if they all had TACC activated? Would "stop and go" conditions develop in a freeway populated entirely by TACC operated vehicles?

There are probably enough Teslas in California now, with the successful launch of the Model 3, that an event could be set up somewhere between LA and SF with a hundred or more Tesla's driving in a large pack. Maybe the organizer could coordinate the pack if everyone tuned to the same webcast.
I think this is what you are describing (more or less... maybe less bar fights)