[NewsCoulomb]

See Chevrolet Bolt EV Range at Constant Speeds

Interesting. I thought I would have come across that before. It's unfortunate that Prof. Roper never updated the calculations based on updated information (e.g., the Bolt EV's Cd is .308, not .312). Also, much of the data he is basing on includes driving with accessories powered on (see my post earlier about how increased base load increases the peak efficiency driving speed). The Car and Driver test at 75 mph constant speed included the climate control set to 72 F on a "warm day." Likewise, the EPA cycle actually includes and accounts for the use of some accessories.

So if we're strictly speaking about peak efficiency speed, I'd assume no systems or accessories. Based on my experiences, climate control at 72 F on a warm day accounts for about 3% to 5% of the total energy consumption when traveling at freeway speeds. At slow speeds, that type of base energy consumption could easily push the peak efficiency speed from ~18 mph to >20 mph.

 

[redpoint5]

Can reducing speed possibly double the range of an ICEV, the way it can in the Bolt?

I get better MPG in gridlock Portland traffic than on the highway when I drive the average (extremely slow) speed of traffic instead of going bumper to bumper in my Acura.

One interesting thing about an ICE is that it produces the most power per fuel at around 75% of maximum torque and 2,500 RPM. This is not the same as best MPG, because it takes tremendously more power to travel at ever increasing speeds. Producing the most efficient power is not the same as traveling at the most efficient speed.

The main reason a car like the Prius can get such good fuel economy is that it has an infinitely variable transmission that can keep the car in the sweet spot of most power per amount of fuel used regardless of speed.

I won't get into the details, but the red portion of this Brake Specific Fuel Consumption map is the most power per fuel burned. There are low torque (throttle position) and low/high RPM bands that consume twice or more fuel to produce a given amount of power.

 

[TFPDrive]

Why not just leave HVAC out of it. That only confuses the question of efficiency.

Because an ICE always has a portion of its energy going towards heat production and there's no way to turn it off.

If you want to compare apples to apples then you have to factor that in.

 

[ga2500ev]

Why not just leave HVAC out of it. That only confuses the question of efficiency.

Because the HVAC is the second biggest consumer of energy in an EV. The consumption is high enough that it affects the overall range of the vehicle. And most importantly, ordinary people are actually going to run the HVAC in hot or cold conditions. It needs to be taken into account.

ga2500ev

 

[PLP]

I love torque maps... I wish they were readily available for all engines in all manufacturers as frankly, for me, this is one of the main deciding factor for purchase of a certain car.
And the power/torque graphs. Darn it. So normal to get this info in Europe, but not in the US. Why?
Funny fact I noticed - in Poland, when I would read an ad about some car, they would say how big is the trunk, what is the power of the engine, what is the fuel economy... in the US the first thing (at least couple of years ago) it was about: how many cup holders, how many speakers, then mpg, maybe how many cylinders.
To find out what is the torque - well, it takes a while. To see the power curve - almost impossible. Ask you dealer.


Anyway, whatever a professors says, or some other graphs - my own tests. Based on 1 example. No error bars here, no standard deviation.
Bolt at 70 mph will do about 3.6 mil/kWh
At 50 mph will do 5.0 mil/kWh.

Q5 at 70 mph will do 28 mpg
at 50 mph will do 35 mpg.

That is summer, no AC use in either case.

Winter? Heck, who knows. But, Q5 will not be affected much, while Bolt - I guess I could estimate assuming 4 kW energy needed to heat the cabin.
My numbers would be like that then:
3.0 vs 3.6 (70 mph and 50 mph respectively)
Interesting how big impact it takes at lower speeds.

 

[NewsCoulomb]

Winter? Heck, who knows. But, Q5 will not be affected much, while Bolt - I guess I could estimate assuming 4 kW energy needed to heat the cabin.
My numbers would be like that then:
3.0 vs 3.6 (70 mph and 50 mph respectively)
Interesting how big impact it takes at lower speeds.

The rule of thumb I've read on hypermiler and ecomodder forums for ICE cars is ~6% efficiency loss for every 10 F the temperature drops. If you go to some of the mileage/fuel economy tracker websites and compare the fuel economies of the same vehicles in, say, Canada versus Florida, you'll see a noticeable difference in fuel economy.

 

[PLP]

The rule of thumb I've read on hypermiler and ecomodder forums for ICE cars is ~6% efficiency loss for every 10 F the temperature drops. If you go to some of the mileage/fuel economy tracker websites and compare the fuel economies of the same vehicles in, say, Canada versus Florida, you'll see a noticeable difference in fuel economy.

Do you think that includes cold start?
I do not see why, when engine reaches operating temp, its efficiency would drop with temperature.
I can see that denser air would cause more fuel use, but not at 6% rate for each 10 degrees F.

From my notes - yes, winter will cause more fuel use, but mainly due to cold start and cabin heater causing longer warm up times. What previously start at +20 C would warm up to +80 C within one mile, now we need 2.5 miles to reach same temp. So any traffic stop, any idle during this time will increase fuel consumption a lot.
I can see rolling resistance due to friction and flex of winter tires and snow coverage.
But again - those I would not factor it as "cold" weather influence.


All city driving - I see easily 10-15% higher fuel use between -15 C winter and +25 C summer. However, any longer trips, where I would fuel up whole tank - barely any change.


On that note - I found Bolt dropping easily 10-15% of efficiency while driving just in rain. That I believe is caused by mainly water on the streets (more friction and all water that was "picked up" by the tires) and the wipers usage.

 

[redpoint5]

Yeah 6% per 10 degrees F isn't right, and as you point out, it depends on how cold things were and how far the vehicle is driven.

I know people that would commute 3/4 of a mile daily. A car doesn't even warm up in that distance. Engine coolant, transmission/gear oil, and engine oil all cause more drag when cold, but the biggest consumption comes from the vehicle running at high idle and rich during the warm up phase. My Prius would run high idle until it reached an engine coolant temp of 130 F. That was probably 3 minutes.

 

[NewsCoulomb]

Do you think that includes cold start?
I do not see why, when engine reaches operating temp, its efficiency would drop with temperature.
I can see that denser air would cause more fuel use, but not at 6% rate for each 10 degrees F.

From my notes - yes, winter will cause more fuel use, but mainly due to cold start and cabin heater causing longer warm up times. What previously start at +20 C would warm up to +80 C within one mile, now we need 2.5 miles to reach same temp. So any traffic stop, any idle during this time will increase fuel consumption a lot.
I can see rolling resistance due to friction and flex of winter tires and snow coverage.
But again - those I would not factor it as "cold" weather influence.


All city driving - I see easily 10-15% higher fuel use between -15 C winter and +25 C summer. However, any longer trips, where I would fuel up whole tank - barely any change.


On that note - I found Bolt dropping easily 10-15% of efficiency while driving just in rain. That I believe is caused by mainly water on the streets (more friction and all water that was "picked up" by the tires) and the wipers usage.

I'm sure it includes all aspects of running the vehicle, including ICE warmup cycles. My Volt consumption goes from ~42 mpg summer to ~36 mpg winter, so it doesn't seem that far off to me. And that is in California and with a PHEV, which only runs the ICE in sustained driving.

 

[PLP]

I'm sure it includes all aspects of running the vehicle, including ICE warmup cycles. My Volt consumption goes from ~42 mpg summer to ~36 mpg winter, so it doesn't seem that far off to me. And that is in California and with a PHEV, which only runs the ICE in sustained driving.

Based on my many cars I traced, the latest one 2016 KIA Forte5 SX.
Summer, my city driving, 24-25 mpg, winter 22-23 mpg. Same style, same trip. That is about 10% drop. Some claim fuel is different... I am not sure about that.
What I used to do, though, before I would turn the heat on, I would let the engine reach at least 60 C (140 F). If I let the heat to come in starting at cold start, I would not see operating temp for the whole trip which is about 10 miles, 25 minutes long.
However, summer wheels-all season, 225/40x18, winter 205/60x16.
Smaller wheel, better fuel economy, but stickier rubber, more flex.

 

[NewsCoulomb]

Based on my many cars I traced, the latest one 2016 KIA Forte5 SX.
Summer, my city driving, 24-25 mpg, winter 22-23 mpg. Same style, same trip. That is about 10% drop. Some claim fuel is different... I am not sure about that.
What I used to do, though, before I would turn the heat on, I would let the engine reach at least 60 C (140 F). If I let the heat to come in starting at cold start, I would not see operating temp for the whole trip which is about 10 miles, 25 minutes long.
However, summer wheels-all season, 225/40x18, winter 205/60x16.
Smaller wheel, better fuel economy, but stickier rubber, more flex.

One thing to keep in mind is that many people do run dedicated winter tires, which affect ICE cars in the same way as they affect EVs. Increased rolling resistance is increased energy consumption, regardless of vehicle.

 

[boltage]

The other thing to note during autumn and winter is that lower ambient temperatures cause reduced tire air pressure that worsens economy, unless the owner is vigilant about checking tire air pressure, particularly during autumn.

 

[Tim]

I'd love to see their calculations, but even for the hypermiling event that Hyundai sponsored, they had their Kona Electric drivers traveling 18 mph.

I'm curious why their Ionic is more efficient than the Bolt. Is it only because of the coefficient of drag?

 

[NewsCoulomb]

I'm curious why their Ionic is more efficient than the Bolt. Is it only because of the coefficient of drag?

Pretty much. The Hyundai Ioniq Electric has a smaller frontal area and a lower coefficient of drag. It's that combined CdA that determines efficiency and range more than almost anything else, especially when considering highway/freeway speed efficiency and range.

 

[PLP]

I'm curious why their Ionic is more efficient than the Bolt. Is it only because of the coefficient of drag?

Look on the shape. Ionic is very short (height), hence less air drag in frontal area.
Not sure about weight. Narrower tires may help as well.

Bolt is quite tall and rear is not really aerodynamic. All hatchbacks suffer from it. Sedans are far better.

 

[roseberry]

If there are no chargers or no working chargers then going slower would definitely be faster due to the reduced walking (or maybe running) time at the end. Also if you have to drive a long distance out of your way to get to the charger, going slower might be faster if it makes using the shorter route possible.

 

[djvollmer]

Today, Chevrolet Program Engineering Manager Rob Mantinan said, "Sometimes driving slower gets you there faster." Meaning that driving slower extends your range and might possibly allow you to skip a charging stop.

How can I determine what the optimal speeds and charging stops are for a particular trip?

Just my observations in 2 years plus with my Bolt. Driving on the interstate @ 70 mph uses about 20 kWh/h so about 3 hours and 210 miles range, hypothetically speaking, of course. Driving on state roads @ 55 mph, I can get about 15 kWh usage so about 4 hours @ 55 mph = 220 miles but driving back roads @ 45 mph, I can get about 10 kWh usage or about 260 miles range. I avoid the interstate whenever I can because I'm cheap, and I'm also retired, and in no rush. Until the infrastructure of charging stations changes, the BEV's are still better at city driving than long distance touring.

 

[XJ12]

If your first stop is 248 miles away, that's going to be a slog.

Such a small world. I had seen a check-in on Plugshare about easily making this drive non-stop in a Bolt. Well, today I meet a guy in town and we got to talk a little bit at a stop sign. The guy has driven his Bolt thousand of miles. All the way from Maine to Southern New Mexico. He even said he's pulled a trailer long distance with it. Immediately looked at his tires on his 2018 and he's running Continental tires. Went back to Plugshare and sure enough, same guy. He said he made it with 50 miles still showing. Asked if him if he was on the Bolt forum and he said no.

 

[sundog]

Today, Chevrolet Program Engineering Manager Rob Mantinan said, "Sometimes driving slower gets you there faster." Meaning that driving slower extends your range and might possibly allow you to skip a charging stop.

I find that this can be true when the high-speed freeway route is a longer distance than a route along secondary roads. It can also be true if driving fast would cause an extra charging stop, but the needed charger is not directly on your path.

 

[tangolima]

Spent an hour thinking about this.

Assumptions. 500 miles trip. Soc 10% to 55% so as to get the top 53kw charging rate. Efficiency 4.4 miles / kWh at 63mph, and is inverse proportional to square of speed.

Cut away the math equations. Here is the short version of the story.

80mph. 6 charges. 9.2hr. 183kwh.
75mph. 5 charges. 9.2hr. 161kwh.
70mph. 5 charges. 9.7hr. 140kwh.
65mph. 4 charges. 9.7hr. 120kwh.
60mph. 3 charges. 9.9hr. 103kwh.
55mph. 3 charges. 10.6hr. 72kwh.

Conclusion. I will continue to drive at 65mph. 30min more, $20 less. It is pretty expense and time consuming to drive EV for road trip.

-TL

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