Chevy Bolt EV Forum banner

1 - 20 of 53 Posts

·
Registered
Joined
·
312 Posts
Discussion Starter · #1 ·
It occurs to me that we have for long seen city/highway/combined MPG figures for cars that consume petroleum products for propulsion. Why do we not see the same for EVs? Why just one "range" figure?

Using just my own anecdotal data, I have experienced around 3.5 miles/kWh when I drive distances on the freeway and I'm maintaining around 70 MPH. That would translate to a range of about 210 miles for 2017-2021 Bolts. If I'm sticking to city driving, I tend to average around 4.5 miles/kWh, for a range of about 270 miles. Why wouldn't it be reasonable to have structured testing like they do for ICE vehicles and report city/highway/combined, either miles/kWh or range, or maybe both, on the sticker?
 

·
Registered
2020 Chevrolet Bolt
Joined
·
791 Posts
It occurs to me that we have for long seen city/highway/combined MPG figures for cars that consume petroleum products for propulsion. Why do we not see the same for EVs? Why just one "range" figure?

Using just my own anecdotal data, I have experienced around 3.5 miles/kWh when I drive distances on the freeway and I'm maintaining around 70 MPH. That would translate to a range of about 210 miles for 2017-2021 Bolts. If I'm sticking to city driving, I tend to average around 4.5 miles/kWh, for a range of about 270 miles. Why wouldn't it be reasonable to have structured testing like they do for ICE vehicles and report city/highway/combined, either miles/kWh or range, or maybe both, on the sticker?
The EPA calculates 127 MPGe for city driving, and 108 MPGe for highway. The conversion from MPGe (miles per gallon equivalent, or miles per energy stored in 1 gallon of gasoline) is mi/kWh ≈ MPGe ÷ 33.705. That gives ~3.77 miles / kWh for city, and ~3.20 miles / kWh for highway.

 

·
Registered
Joined
·
5,389 Posts
It would be good if highway and city range was made more apparent to customers, since range is a primary concern to EV owners.

As an aside, the EPA develops the testing regimen, and manufacturers submit the results of their own testing to be published by the EPA. That's why we see larger discrepancies in the accuracy of Tesla range vs the Bolt, for instance. Manufacturers often get away with fudging the numbers unless they are so apparently off that a lawsuit gets them to adjust the figures. The Ford C-max had an extremely high MPG rating until such a process forced them to adjust the rated MPG.
 

·
Registered
2020 Chevrolet Bolt
Joined
·
791 Posts
It would be good if highway and city range was made more apparent to customers, since range is a primary concern to EV owners.
So the interesting thing is that the overall EPA range (259 miles) is actually higher than what you would calculate from the highest MPGe rating. Even if the 2021 Bolt had a full 67 66 kWh battery (and there's reason to suspect that's just a marketing number), 67 66 kWh x 3.77 miles / kWh = 252.6 248.8 miles < 259 mile EPA range.

Edit: corrected advertised battery capacity from @wesley below.
 

·
Registered
2021 Bolt LT - Kinetic Blue
Joined
·
54 Posts
I have regularly used the "Personalize" button on fueleconomy.gov and adjusted the number for percent in stop and go traffic (55% is default) to get this information. And I agree with @liuelson that doing the math for battery capacity (gross or net) and the rated efficiency doesn't multiply out to the range indicated according to the same rating agency.
 

·
Registered
2018 Bolt EV Premier
Joined
·
892 Posts
So the interesting thing is that the overall EPA range (259 miles) is actually higher than what you would calculate from the highest MPGe rating. Even if the 2021 Bolt had a full 67 kWh battery (and there's reason to suspect that's just a marketing number), 67 kWh x 3.77 miles / kWh = 252.6 miles < 259 mile EPA range.
Certified miles/kWh figure takes losses during the charging-discharging process into account. Therefore you cannot simply multiply the battery capacity number to get the drivable range, or divide the battery capacity from the drivable range to get the miles/kWh number.

Korea's Ministry of Environment uses a method of testing similar to US EPA and certified Bolt 2017-2019 to have 383km (238 miles) of range while having 5.5km/kWh (3.4 miles/kWh) combined efficiency and 60.9kWh of battery capacity.

5.5km/kWh * 60.9kWh = 335km is nowhere near 383km, due to the aforementioned losses.

Also, GM marketed 2021 Bolts as having 66kWh battery, not 67.
 

·
Registered
Joined
·
73 Posts
In the ICE world, mpg was really all about money, not range. Potential EV buyers worry more about range, but they also want to know about money savings...but varying gas prices and stable but very different by locality/electric provider make that a variable number. For us, we average about 3.75miles/kWh and pay about $0.105/kWh for electricity. Regular gas seems to be about $3.38 a gal this morning in my area. That means we can get about 32.2kwh for the price of a gallon of gas.
Therefore: We get equal to 121mpg today...pretty much just what the sticker said we would

But since it changes everyday, maybe we need an app(not made by Chevy) that stays updated on you average mi/kWh and the current daily gas price and calculates the equivalent mpg to show your ICE friends.

OTOH, I also have an ICE and I don't like to think about how much its costing me to drive vs the Bolt...maybe keep these numbers to ourselves. :)
 

·
Registered
Joined
·
312 Posts
Discussion Starter · #8 ·
In the ICE world, mpg was really all about money, not range. Potential EV buyers worry more about range, but they also want to know about money savings...but varying gas prices and stable but very different by locality/electric provider make that a variable number. For us, we average about 3.75miles/kWh and pay about $0.105/kWh for electricity. Regular gas seems to be about $3.38 a gal this morning in my area. That means we can get about 32.2kwh for the price of a gallon of gas.
Therefore: We get equal to 121mpg today...pretty much just what the sticker said we would

But since it changes everyday, maybe we need an app(not made by Chevy) that stays updated on you average mi/kWh and the current daily gas price and calculates the equivalent mpg to show your ICE friends.

OTOH, I also have an ICE and I don't like to think about how much its costing me to drive vs the Bolt...maybe keep these numbers to ourselves. :)
Holy cow, while my electric bill just got more complicated (apparently the actual electricity cost is now coming from "San Jose Clean Energy," which seems to charge 6.6 cents/kWh for the lowest tier and 7.6 cents/kWh for the next tier, which PG&E still bills for "delivery" and charges 26 cents/kWh), the latter is WAY more than you. Then again, gas prices within a few miles of here range from #3.79/gallon (Costco) to $4.79/gallon (who pays this?).
 

·
Registered
Joined
·
312 Posts
Discussion Starter · #9 ·
The EPA calculates 127 MPGe for city driving, and 108 MPGe for highway. The conversion from MPGe (miles per gallon equivalent, or miles per energy stored in 1 gallon of gasoline) is mi/kWh ≈ MPGe ÷ 33.705. That gives ~3.77 miles / kWh for city, and ~3.20 miles / kWh for highway.

Problem with that is that MPGe is practically useless for comparison to ICE cars because how many "gallons" are in a battery? Whoever came up with that was clearly an engineer, not someone who understood how to communicate concepts clearly.

I mean, an ICE car has, say, a 12-gallon tank and it gets 35 MPG, so it's range is 420 miles. The Bolt (at least the 2017-2019 models) has a (usable) 60 kW battery and gets 4 miles/kW, so its range is 240 miles (OK, 238). How hard is that?
 

·
Registered
Joined
·
4,365 Posts
Holy cow, while my electric bill just got more complicated (apparently the actual electricity cost is now coming from "San Jose Clean Energy," which seems to charge 6.6 cents/kWh for the lowest tier and 7.6 cents/kWh for the next tier, which PG&E still bills for "delivery" and charges 26 cents/kWh), the latter is WAY more than you. Then again, gas prices within a few miles of here range from #3.79/gallon (Costco) to $4.79/gallon (who pays this?).
Sounds like you need to get solar and home battery system...
 

·
Registered
Joined
·
14 Posts
Problem with that is that MPGe is practically useless for comparison to ICE cars because how many "gallons" are in a battery? Whoever came up with that was clearly an engineer, not someone who understood how to communicate concepts clearly.
No self-respecting engineer would come up with a unit of measurement that silly. That had to be a Marketing request. Same thing when you see comparisons to numbers of football fields/elephants/school buses/average cars.
 

·
Registered
Joined
·
8,681 Posts
This is what I tell people that want to talk about my Bolt. Tell them that it holds the equivalent of gas that my riding lawn mower has and my car gets 130 mpg. For years, everyone wanted a car that would get over 100 mpg. It's here folks.
Yes! And all they do is whine.
 

·
Registered
Joined
·
4,365 Posts
No self-respecting engineer would come up with a unit of measurement that silly. That had to be a Marketing request. Same thing when you see comparisons to numbers of football fields/elephants/school buses/average cars.
This is because we are a backwards country stuck on the English system and using MPG as a measurement of efficiency, which is ridiculous in itself. Metric countries use Liter per KM which makes more sense.
 

·
Registered
Joined
·
14 Posts
This is because we are a backwards country stuck on the English system
Which works just fine, thank you very much. I use it every day in my engineering job, and our products still work just fine.

Yes, metric is computationally convenient when converting between units of the same dimension, and it is more widely used, but metric units don't have some kind of God-given inherent superiority. A centimeter is not inherently better than an inch; that's like arguing seven is a better number than five.

and using MPG as a measurement of efficiency, which is ridiculous in itself. Metric countries use Liter per KM which makes more sense.
More sense to who, and in what situation? If you're capable of doing middle school math, you can work out whatever you need regardless of whether your measurement is (distance)/(fuel quantity) or (fuel quantity)/(distance). For example, if I have a certain amount of fuel, miles per gallon is quite a useful measurement; I merely need to multiply it by fuel quantity to see my available range.

Which one makes "more sense" to you is likely just a factor of which one you are accustomed to using.
 

·
Registered
Joined
·
4,365 Posts
  • Like
Reactions: micantony

·
Registered
Joined
·
4,365 Posts
Yes, metric is computationally convenient when converting between units of the same dimension, and it is more widely used, but metric units don't have some kind of God-given inherent superiority.
Yes, thank you for making my point. LOL
 

·
Registered
Joined
·
118 Posts
It's a different way of looking at things. The MPG way of thinking is "How far can I go with the fuel that I have?" while the liters/100km approach is more like "What will it cost to get me to my destination?".
 

·
Registered
Joined
·
4,365 Posts
Generally, the newer adopted method is superior. Makes sense, why would people adopt a new method of the older one was superior. Switch from horse to car means no poop all over the road. Switch from car to EV means no pollution all over the city/town/world.
 
1 - 20 of 53 Posts
Top