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Discussion Starter #1 (Edited)
I collected some data from other Volt owners that posted their real data here. I just ran a rudimentary regression analysis to find the best predictive equation. The predictive equation is only valid for speeds of 20 - 80 mph.

To use the equation, simply do the % change calculation based on your typical EV range at 55 mph. The main point of the analysis is to show how big of a price the electric car mode of the Chevy Volt has to pay at higher speeds, much higher penalty than the ICE cars.

For example, according to studies backed by the department of energy, the average car will be at its advertised MPG at 55 mph. But as the speed increases:
- 3% less efficient at 60 mph
- 8% less efficient at 65 mph
- 17% less efficient at 70 mph
- 23% less efficient at 75 mph
- 28% less efficient at 80 mph

But for the Chevy Volt, the penalty for the EV Range is greater:
- 9% less efficient at 60 mph
-17% less efficient at 65 mph
-26% less efficient at 70 mph
-35% less efficient at 75 mph
-45% less efficient at 80 mph

My predictive equation:

% Change in EV Range = 47.11*sqrt(x) - 4.58x - 99.5

where x = speed, mph.
 

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One of the biggest issues with Volt gas mileage numbers is that the gas engine often does not get used much. If someone is driving less than 100 miles, true mpg may not be very good because the engine is only using a gallon or two.

On a recent mostly-highway 350 mile trip -- with highway speeds ranging from 55mpg to 75mph, I was able to get 41mpg (gasoline only). This beats EPA (37 mpg combined) by 4 miles.

ps: There is no local vs highway breakup for Gen 1 Volt but it is typical for highway to be more efficient to local on regular gasoline cars, and vice versa for hybrids.

So, with a Volt, YMMVVVW (Very Very Wildly) :)
 

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Discussion Starter #3
One of the biggest issues with Volt gas mileage numbers is that the gas engine often does not get used much. If someone is driving less than 100 miles, true mpg may not be very good because the engine is only using a gallon or two.

On a recent mostly-highway 350 mile trip -- with highway speeds ranging from 55mpg to 75mph, I was able to get 41mpg (gasoline only). This beats EPA (37 mpg combined) by 4 miles.

ps: There is no local vs highway breakup for Gen 1 Volt but it is typical for highway to be more efficient to local on regular gasoline cars, and vice versa for hybrids.

So, with a Volt, YMMVVVW (Very Very Wildly) :)
The equation is only for the EV Range. When you put the car in hold mode, and with its CVT, it would be a different predictive model, most likely to follow that of the ICE cars.
 

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I collected some data from other Volt owners that posted their real data here. I just ran a rudimentary regression analysis to find the best predictive equation. The predictive equation is only valid for speeds of 20 - 80 mph.

To use the equation, simply do the % change calculation based on your typical EV range at 55 mph. The main point of the analysis is to show how big of a price the electric car mode of the Chevy Volt has to pay at higher speeds, much higher penalty than the ICE cars.

For example, according to studies backed by the department of energy, the average car will be at its advertised MPG at 55 mph. But as the speed increases:
- 3% less efficient at 60 mph
- 8% less efficient at 65 mph
- 17% less efficient at 70 mph
- 23% less efficient at 75 mph
- 28% less efficient at 80 mph

But for the Chevy Volt, the penalty for the EV Range is greater:
- 9% less efficient at 60 mph
-17% less efficient at 65 mph
-26% less efficient at 70 mph
-35% less efficient at 75 mph
-45% less efficient at 80 mph

My predictive equation:

% Change in EV Range = 47.11*sqrt(x) - 4.58x - 99.5

where x = speed, mph.
Because the ambient temperature is such a large control of the mileage, and is missing from this equation, the equation is badly off at best. You also have to factor in if the heat is turned on in cold weather or if Air con is running in hot weather.
The speed effects to mileage is affected around 45 to 55. It is a mild ramp up from 0 to 40, it gets much steeper 45 to 55 and above this you lose at least half or your estimated mileage, again, temperature considered.
Then factor in driving habits.........................................
 

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I think you're correct that EV range drops faster than ICE range at high speeds. Most owners switch to gas at highway speeds and that creates a problem with lack of data other than a few Volt owners posting here. My only experience was with our 2013 which would drop 20% at 75 mph not 35% as your data shows.
 

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Discussion Starter #6
Some of you folks misunderstood how to use the predictive equation. You just have to know how to use it. It is in a normalized form because it is expressed in terms of percentage change, not the absolute range, so it is quite very accurate across a wider range of temperature. Remember that the predicted percentage change is based on the EV Range of your driving profile at 55 mph. If you assume the same conditions and you drive at a different speed, your percentage change in EV range is predicted quite well.
Let us take for example these various cases:

Temperature is 40 deg F, and you turned on the heat, so that your typical range when driving at 55 mph is 45 miles. Now, using the same heat settings, same road conditions and ambient temperature, you drove at 65 mph, and my prediction says, you would lose 17% range, so your range would be 37 miles.

Another scenario, temperature is 80 deg F, and you just use the fan, so that your typical range when driving at 55 mph is 65 miles. Now, using the same car settings, same road conditions and ambient temperature, you drove at 65 mph, and my prediction says, you would lose 17% range, so your range would be 54 miles.

So you see, it has built-in normalization, and it indeed requires the range information at the base reference of 55 mph! If you know that EV range, you should be able to accurately project your range at various speeds assuming the same ambient conditions as that in 55 mph. Of course, the prediction would become iffy when you are trying to project it in very extreme ambient conditions which is not within the scope of the data.
 

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Good work Joe!

ICE engines operate at a higher BSFC (think of it as economy) at higher throttle openings.
So 2 identical cars, one with EV power and the other with ICE will behave differently.
In my personal experience, this holds true with the Volt as well. The drop in my ICE MPG between 60 and 75mph is a smaller % than the drop in EV mode, especially on steep grades.
So when I know I will run out of juice, I try to pick an uphill or upwind long stretch and use HOLD. I try to only use it once and turn on the ICE a mile or two before the high speed or uphill area so the engine warms up. ICE engines get more MPG at max operating temperature as well.
 

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HELLO Looks simliar to the Gen 1 curve, which has actual miles. Asssuming some constant Temp. With the Gen 1 there is a slight drop below 24MPH something (??) according to some testing Ari did. Hope I spelled his name right.
No doubt given all things equal. Velocity is the biggest factor, temp being a very close secound. Assuming mild Accelerations, which could be the largest.
 

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The fun thing is that for the observed results, the drop in efficiency is nearly linear anyway.

Note That the a graph done by others for a GEN 1 does not show a linear relation to speed, which makes more sense to velocity squared. See post 44 In below thread. Maybe sort linear, but not linear. Friction and other variables even out the line to be sort of linear. But there is a definite diff between GEN 1 and Gen 2 or the graph data is off.

http://gm-volt.com/forum/showthread.php?8235-MPGe-at-Various-Speeds/page5
 

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I have never experienced mpg changes even close to the predicted magnitude for higher speeds. My 1 ton van gets 18mpg at 75, it doesn't get even 20% better at 55. At best it might get 1 mpg better, which is only 5%. Same with my tdi. It has done 50 mpg at 75. It would not even do 55mpg at 55 mph.
There must be large changes of bsfc in Diesel engines that negate the increase in energy required to go faster.
 

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I have never experienced mpg changes even close to the predicted magnitude for higher speeds. My 1 ton van gets 18mpg at 75, it doesn't get even 20% better at 55. At best it might get 1 mpg better, which is only 5%. Same with my tdi. It has done 50 mpg at 75. It would not even do 55mpg at 55 mph.
There must be large changes of bsfc in Diesel engines that negate the increase in energy required to go faster.
There are non-trivial "hump" in the curve for particular RPMs in particular gears, which can make particular models run more efficiently at some particular points than other arbitrary points. But that doesn't change the overall curve, nor does it mean that there's a predictable path between peaks.

https://en.wikipedia.org/wiki/File:Fuel_economy_vs_speed_1997.png
 

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As for me, when I am about to go over 50 mph for an extended period of time, like more than a couple of miles of road, I would switch to hold mode... And even if I go 70 mph, I get about 15%-20% penalty in combined range, almost the same as the ICE penalty, as my Fuel Tank range estimates changes... And then when speeds go down consistently to below 55 mph, I switch to normal mode, especially during the last stretch, I made sure I used the battery charge all up. So my total EV Range for the trip always exceeds 60 miles per charge and doesn't get penalties from speed. My MPG cs is consistently at 45 mpg now.
 
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