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Creating a thread to gather data on how speed affects electric range. I noticed that at 75mph my electric range seems terrible - but at 60mph it seems much better. Anyone with a regular highway commute - so we can get multiple datapoints under the same conditions - any data to share (total range, or miles per kWh at various speeds)?
 

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Aerodynamic drag which is the more dominate factor at highway speeds, is a function of the square of the velocity. So 60mph to 75mph is a 25% increase in velocity, but drag goes up by a factor of 56% and range will drop accordingly.

VIN # B0985
 

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Discussion Starter #5
Aerodynamic drag which is the more dominate factor at highway speeds, is a function of the square of the velocity. So 60mph to 75mph is a 25% increase in velocity, but drag goes up by a factor of 56% and range will drop accordingly.

VIN # B0985
So if at 55mph if I get 60 miles range, at 75 I will get only 32 miles range?
 

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So if at 55mph if I get 60 miles range, at 75 I will get only 32 miles range?
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

See the graph below (from fueleconomy.gov):



So in you example, you'd be getting 46 miles of range at 75 mph.
 

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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

See the graph below (from fueleconomy.gov):



So in you example, you'd be getting 46 miles of range at 75 mph.
Those numbers are estimates for *ICE* vehicles, which tend to get better fuel economy in highway driving cycles vs city.

In contrast, the Volt does better in electric mode in city driving and slower speeds than on the highway. So you would expect the efficiency penalty for high-speed driving in the Volt to be more severe than the numbers given above.

On the other hand, the Volt is more aerodynamic than the average car too. So maybe these 2 factors cancel each other out(?).

Regardless, the general concept still applies. Faster speed = lower efficiency.
 

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not only does speed kill, it kills your mpg.

I generally try to plan my trips so as to not make driving above 68 a necessity, despite speed limits at 70 plus. I can kep a Gen I at 37 to 41 mpg if I keep the speed down on long trips. I try to hold once on the highway and save the juice for in town but 3 mile per kw is doing good at 68.

I am just not important enough to worry about my trip taking a few extra minutes. and I got XM......
 

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This site is great for modeling speed vs efficiency.
http://ecomodder.com/forum/tool-aero-rolling-resistance.php

Most EVs are not geared for faster than 80 mph efficiency, so drivetrain efficiency might drop at higher speeds, which might not be accounted for by the tool.

This tool will let you model different tires and such, but takes some research to configure appropriately.

PS, I look at watt figure, and for my 2012 I compare it to 9.4 kWh capacity. So if at 80 mph it takes about 26.6 kw to move the Volt, I would estimate my range to be 9.4 kwh/26.6 kw * 80 mi/hr = 28 mile range. At 60 it would be more like 35 miles, and 40 more like 50 miles. This is very close to what I get.

I used 1 kw overhead, .28 Cd, 23.7 sqft area, .013 tire coeff (use 0.01 or less for lrr tires), engine 0.33, drivetrain 0.9, 4000 lbs, rest default. The tool could allow different parameters for different speeds, but it doesn't so you might figure out high speed and low speed models separately.

The cool thing once you have your model setup, you can accurately figure what adding a passenger, changing tires, etc will do to your efficiency.
 

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In general, I don't worry too much about efficiency. Getting there faster is more important as my time is money. If I go above 70mph, I generally use Hold so I have some juice left for the neighborhood at the other end.

Parts of my commute, if I choose to use the toll road, are posted at 75mph and I hit 80-85 there. Since the toll road's posted price goes up as congestion on the main roads increases, I generally take the toll road when it is above $5 and get the best bang for my buck. $5 generally gives me back 1/2 hour.

IOW, my decision to DIY (or take a slower route) hinges on: is it saving me more than $20/hour in Psych fees.

And to answer the question, I can use ~6kWh in 5 miles @ 85mph. '14 ELR.
 

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True to the OPs original details where they stated 75MPH, are there any vehicles that can even get 40MPG that aren't diesel at 75MPG? The often touted 53 miles of range of the Gen2 is combined, it gets just under 57 city and just under 49 HWY...
 

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I have a 56 round trip commute which is mostly highway and after testing speeds I've found 68 MPH I can just about make it to work & back on all electric. The generator kicks in at the last couple miles. I've just got my HOV sticker & tried doing 70 MPH & I definitely noticed a big change. I'm in S FL so heat is a factor now with a/c working hard.

2017 volt
 

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I think it really comes down to the kWh used at your current speed. My commute is 55 miles one way to work. From home to work I have a short climb and then it is mostly downhill from there on the highway. On the uphill parts I keep it at 60mph and the downhill parts I crank it up to whatever the traffic is going, typically 70-75, and I ease off the accelerator and coast, letting regen charge a bit. Going to work I get around 80 miles range. On the way home, since it is mostly uphill I keep it at 60 mph and get 50-65 miles range.

More importantly I try not to go over 30kWh at any speed, unless it puts me at too low of a speed for traffic. That seems to help the most. 15kWh and below is a pretty good target to hit on flat surfaces.
 

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Discussion Starter #17
Extrapolating from the link above, assuming 14 usable kWh:
Speed / EV mi
30 67
35 65
40 63
45 61
50 57
55 55
60 47
65 44
70 42
75 35
 

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Creating a thread to gather data on how speed affects electric range. I noticed that at 75mph my electric range seems terrible - but at 60mph it seems much better. Anyone with a regular highway commute - so we can get multiple datapoints under the same conditions - any data to share (total range, or miles per kWh at various speeds)?
Is this in some way surprising that higher speeds reduces range?
 

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Hello What is not so obvious is that degree with which MPH effects range and how this is not readily available data for new owners. Took me awhile to see that 30MPH was a peak point. Mile/KW is a good comparison between different cars, but without knowing the MPH does not say much.

The link below had data from a Dynamo which some what supports the below numbers after dividing 14KW-hrs/ (WH/m). ie at 60MPH they had 294 WH/m, 14/.294=47miles


Extrapolating from the link above, assuming 14 usable kWh:
Speed / EV mi EV from Dynamo (added)
30 67 77
35 65
40 63 67
45 61
50 57 55
55 55
60 47 47
65 44
70 42 38
75 35

http://gm-volt.com/forum/showthread.php?246218-60-Plus-miles/page3
 

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Remember, Ari_C achieved 81.8 miles in a gen1 with a smaller battery, but driving 20-25 mph in a closed loop for 4 hours. I agree with loboc, just drive and don't worry about the range. if the meter wasn't sitting front and center on the dash, (like in many ice vehicles) you wouldn't give it a second thought. Black electrical tape works well.
 
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