Possible reasons:

• Different temperatures (morning vs afternoon)
• Different humidity with auto-defog turned on in the settings
• Different use of A/C or heater
• Different terrain (uphill / downhill)
• Different wind depending on presence of trees
• Different drafting effect behind other vehicles

etc.

 

so...
The variation was all within 1 hour on one trip.
No auto-defog or any climate control at all.
No hills, flat Florida roads.
The roads were not super busy so I could verify that it was not a drafting effect.
I could verify that transitioning from a wooded area to a swamp did not make any difference.

 

I have been surprised by the large effect that rain has on my efficiency. I assume this is due to pushing through the water on the road, rather than in the air. With that in mind, I can imagine that the road surface could have a noticeable effect.

 

The water already on the road seems to be the major source of drag on a rainy day. Not so much for the falling rain (i.e. water suspended in the air) unless it was a heavy, thick downpour. I have seen the efficiency drop by up to 20% on a rainy day with watery road.

 

It's tricky to read your OP because I think (?) you started leaving out the decimal point in your Bolt-reported average efficiency number of miles per KWH. Is that right? It would also be helpful to know if you reset the trip odometer with the check-mark button before each section you measured. Or was it the cumulative number with no odometer reset? I rarely get to go 80MPH, so I don't yet have an observation on Bolt efficiency at very high speeds, when EVs do their worst.

 

I did not leave out the decimal. I was quoting the observed power use, not efficiency. Thats why I said kw, not kwh. Efficiency can be back-calculated from the power use at a given speed. The efficiency I quoted was for the entire 55 or so miles of highway travel. I started out after an overnight charging session so it was easy to see.

I did have the car in L mode, so when I did slow down for traffic I got some back, but doesn't seem like that much and the slow-downs were only from 80 to 70ish every now and then.

I will see how the drive home goes and update this post.

 

Prevailing wind direction can have more of an effect than you might think. You may have had a tailwind on the highway where you got the lower power reading. Also, I'm in Florida and it is flat here. But not THAT flat! If you travel for an hour on a highway that looks flat and then look at a topo map of where you started versus where you are now, you often find something like a 50 to 80 ft difference in elevation. That can only mean one thing: your whole drive wasn't flat even though it felt flat. It's often difficult to judge a slight uphill or downhill.

Mike

 

Prevailing wind direction can have more of an effect than you might think...

The force of air resistance varies with the square of velocity, and power is force x velocity, so power varies with the cube of velocity. A 1 mph difference in wind (head vs tail) at 80 mph could cause a ~8% difference in power required to overcome air resistance (81 cubed vs 79 cubed). Air resistance isn't the only thing that determines the total power consumed, but it is the one most affected by speed (cubed).

 

Hi everyone. I just purchased my 2020 LT as a dealer loaner with 2k miles on it. For the past 2 days I have commuted back and fourth to work, about 60 miles 1 way, about 80% highway. I set my cruse to 80 mph on the highway, which is not at all unusual here in Florida, and can maintain it, except for a few variations here and there except for going around an occasional slower car. This morning I did the trip on a different route, a few miles longer with more highway travel, closer to 90%. All on flat level Florida roads, typical of east central Florida.
First... I got 3.2 mi/kwh for the highway portion of the trip. I was very surprised at this. I did not expect to get over about 2.8.
Second, which leads me to my question to the group, I took 3 different highways on my route this morning. On the first, a 4 lane toll road heading east, I averaged around 26 kw of power use. On the second, which is a 4 lane rural road thru the woods and a swamp, I averaged about 30 kw. On the third, I-95 heading south, I averaged about 25 kw. All of this was with cruse control set to 80 on flat strait Florida roads. I do not understand the variation in power from road to road. Has anyone else ever seen this? Tires at 38 psi, very little wind, 60 deg. outside, FYI...

I have a 2019 Bolt. In Las Vegas city driving (75% street/25% highway), I can usually get up to 5 miles/kwh. This is during the season with no heater/ac. I take great pains to nurse as many miles out of each kwh. A lot of regenerating and intersecting light timing. I suppose I annoy a lot of people behind me, but that is what the other lanes are for.

 

Sunday, for the first time, I had a chance to check efficiency on a little longer trip and neutral weather. Wife, myself, daughter, heavy box in "trunk", likely 425lbs total. Drove in "L" the whole time.
-1st leg: Beginning elev. 4350, temp 68F, CC on fresh, no heat or AC, fan lvl 4; 58.7 miles 90% highway at 80mph, ending elev. 4750 17.3 kWh used or 3.39mil/kWh
-2nd leg: Beginning elev. 4750, temp 72F, CC on fresh, no heat or AC, fan lvl 4; 62.6 miles 90% highway at 80mph, ending elev. 4350 15.1 kWh used or 4.15mi/kWh
-Total: 121.3 mi, 32.4 kWh used or 3.74mi/kWh
Elevation and possible headwind/tailwind likely account for disparity of efficiency between legs, but I was happily surprised by the overall efficiency considering the avg. speed!
edit for typo

 

E-Nigma, that is really good, especially the uphill leg.
before I bought the car I watched Youtube of several people, like Bjorne, NewsCoulomb and Out-of-Spec, do range tests. This is what set my expectations. InsideEV's/Out-of-Spec Motoring did a range test of a 2020 at 70 MPH on back-and-fourth trips and got around 3.3 mi/kwh. 2 different people did the test and got similar results.

 

Sort of looking forward to getting some more data points...kinda geeking out on all this stuff. OTOH, I am assuming this was really a high outlier; following numbers sadly may not be as good.

 

Along these same lines, has anyone done any actual measurements of how much elevation change effects efficiency? My rough estimates have shown I use about 2kWh extra per 1000' of climbing at about 55mph. This is on a route that climbs 2500' over 20 miles. Does speed have any real impact on this calculation? Obviously faster uses more, assuming my 2kWh/1000' extra is accurate at 55mph, would it be much different at 45 or 65mph?

 

Just a theoretical calculation...Work (energy) is weight raised by a height, so:

1313 kg x 304.8 m x 9.8 m/s/s = 3. 92 MJ = 1.1 kWh, so not too far off.

 

My day to day driving seems to be the same. 4 miles to work and 4 back and one trip to the store. I could charge once a month but top it off every week. All of my driving is under 45mph.

 

Hi everyone. I just purchased my 2020 LT as a dealer loaner with 2k miles on it. For the past 2 days I have commuted back and fourth to work, about 60 miles 1 way, about 80% highway. I set my cruse to 80 mph on the highway, which is not at all unusual here in Florida, and can maintain it, except for a few variations here and there except for going around an occasional slower car. This morning I did the trip on a different route, a few miles longer with more highway travel, closer to 90%. All on flat level Florida roads, typical of east central Florida.
First... I got 3.2 mi/kwh for the highway portion of the trip. I was very surprised at this. I did not expect to get over about 2.8.
Second, which leads me to my question to the group, I took 3 different highways on my route this morning. On the first, a 4 lane toll road heading east, I averaged around 26 kw of power use. On the second, which is a 4 lane rural road thru the woods and a swamp, I averaged about 30 kw. On the third, I-95 heading south, I averaged about 25 kw. All of this was with cruse control set to 80 on flat strait Florida roads. I do not understand the variation in power from road to road. Has anyone else ever seen this? Tires at 38 psi, very little wind, 60 deg. outside, FYI...

Road material?
could each highway you used have different friction levels?

I would tend to believe the differences are wind resistance, but just throwing out ideas.

 

As others have said, wind is the most likely culprit, especially at those speeds. Even a 5mph wind will make a huge difference at 80MPH as that would be a 10MPH delta if it is head/tail wind. I am in S.FL, and there is always at least a 5mph wind blowing.

 

Hi everyone. I just purchased my 2020 LT as a dealer loaner with 2k miles on it. For the past 2 days I have commuted back and fourth to work, about 60 miles 1 way, about 80% highway. I set my cruse to 80 mph on the highway, which is not at all unusual here in Florida, and can maintain it, except for a few variations here and there except for going around an occasional slower car. This morning I did the trip on a different route, a few miles longer with more highway travel, closer to 90%. All on flat level Florida roads, typical of east central Florida.
First... I got 3.2 mi/kwh for the highway portion of the trip. I was very surprised at this. I did not expect to get over about 2.8.
Second, which leads me to my question to the group, I took 3 different highways on my route this morning. On the first, a 4 lane toll road heading east, I averaged around 26 kw of power use. On the second, which is a 4 lane rural road thru the woods and a swamp, I averaged about 30 kw. On the third, I-95 heading south, I averaged about 25 kw. All of this was with cruse control set to 80 on flat strait Florida roads. I do not understand the variation in power from road to road. Has anyone else ever seen this? Tires at 38 psi, very little wind, 60 deg. outside, FYI...

I'm guessing that the battery was cool and less efficient in the morning, and warmed by use and ambient temperature later, giving better readings.

 

so... on my return home trip yesterday I got similar results. I got around 25kw power use on the interstate, going north. Switching to the toll road heading west/inland I was getting around 28-30 kw average. I ended up with 3.1 kwh/mi efficiency for the entire trip, about 90% highway. Again, I had the cruise set to 80. I am very happy with this. I was expecting around 2.8 or so.
As a side note, I took it up to 90 and set the cruise for about a half a mile during the return trip to see the power use. It stayed steady at 35 kw. Just incase anyone is interested. I think this means the bottom range advertised by the Chevy engineers of 160 miles at 93 mph is a bit high buy not by much.
This morning I headed out. When I got out onto the rural 4 lane road (65 mph speed limit) and set cruise to 80 I was getting steady 30-32 kw power use. When I got onto the interstate heading south It dropped to around 25 kw. All set to 80 mph on the cruise. I am not really sure why I get this variation from road to road but I think I need not obsess over it and focus on the overall trip efficiency. I am not sure if this is common or not.
I never looked at driving like this before. You don't have the ability to, basically, see your instantaneous efficiency in an IC car the way you do in the Bolt. I guess I need not care so much until I am trying to take longer trips. Its new to me so I am feeling out the capabilities and limits. If I need range I will just take the Tiguan on the trip.
The bolt is a great car to commute with as a replacement my HHR with 192000 miles on it, especially with the HUGE discounts I got on it. The discounts and incentives are what made me finally pull the trigger. How can you beat pricing in line with an IC car of similar size but with the added bonus of savings on fuel, and borderline hot-hatch performance on top of it all.