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Discussion Starter · #1 ·
Drove from The Woodlands to Dickinson.

Full Tank of Gas
Radio at Half Volume with Bass
Temp. 90-101f
1 Hour of night driving
Eco Mode AC set to 75
Tire PSI 40-41

Thinking about running 45 but not sure with the heat down here.

All driving done in right lane or center right lane.
Stayed between 60-65 Posted Speed Limits
Made one pass over 70mph

I tested MPG running the ICE in both MM and CS mode.

Starting drive with MM enabled

A 70.4 1.1 gal 64 mpg
B 45 1.0 gal 41 mpg

I reset B trip meter when the ICE engaged.

Stopped at destination wrote down numbers and returned the vehicle to Normal Driving Mode.

again reset B trip meter when the ICE engaged.

A 69.2 1.2 gal 57.2 mpg
B 55.5 1.2 gal 45.8 mpg

140 Miles 61 MPG

I just wanted to see what the car could give me in ICE and came away impressed with the 45 MPG highway.
 

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Keep in mind that at higher speeds efficiency is all about aero, which depends in part on how dense the air is. Hot air is less dense than cold air and, important in Houston, humid air is less dense than dry air. Your tire pressure shouldn't matter that much at these speeds so I'd opt for lower pressure and a nicer ride.
 

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Discussion Starter · #4 ·
Had to go look myself.

Water vapor

The addition of water vapor to air (making the air humid) reduces the density of the air, which may at first appear contrary to logic.

This occurs because the molecular mass of water (18 g/mol) is less than the molecular mass of dry air (around 29 g/mol). For any gas, at a given temperature and pressure, the number of molecules present is constant for a particular volume (see Avogadro's Law). So when water molecules (vapor) are added to a given volume of air, the dry air molecules must decrease by the same number, to keep the pressure or temperature from increasing. Hence the mass per unit volume of the gas (its density) decreases.

The density of humid air may be calculated as a mixture of ideal gases. In this case, the partial pressure of water vapor is known as the vapor pressure. Using this method, error in the density calculation is less than 0.2% in the range of −10 °C to 50 °C. The density of humid air is found by:

http://en.wikipedia.org/wiki/Density_of_air

The drive for me was just confirmation the car is very efficient even while not on battery.
 

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Are you sure about this?
Yeah, he's right about humidity. That is why an airplanes performance is so much worse in extreme humidity. It's all about the air molecules going over the wing. With more water in the air there is less room for the air molecules per volume. Try taking off in a Cessna 172 from a short field with high humidity, temperature and elevation. Not Good! Ask me how I know.

Dan
 

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I believe your stats also show that running the ICE in MM at highway speeds seems to have no adverse affect on mileage, whereas running it a lower speeds uses more gas than running the ICE in Normal.
 

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I would keep the tire pressure at the manufacturer recommended 35 PSI (cold). They are low rolling resistance tires, and you are just subjecting them to extra wear and abuse, not to mention yourself with the ride. 40 MPG in CS mode is not that unusual for me, without taking all the extreme steps.
 

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I am usually doing around 32mpg on ICE in Houston. Sometimes it's as high as 35mpg. I don't see how I could ever get over 40.
 

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@voltage692. How fast do you drive? Are you doing a good job of keeping the bouncing ball in the center? Do you precondition the cabin? I did that this morning for the first time. I did my 45.8 mile ride into work and still have 5 miles left of battery. Preconditioning made a large difference. I had the inside temp set to 72, the outside temp was 81, 1/3 of the drive was at 75 mph, 1/3 at 65, and 1/3 at 55 on two lane country roads. The climate setting was on auto and econ. The headlights were on automatic.

For longer drives with the same settings I've been getting 39-40 mpg using the ICE. I think if the freeways here were more conducive to driving slower than 65 the ICE mileage would be even higher.
 

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I drive about 60% of the time at 70mph on the freeway and the other 40% is city driving around 40mph with lots of stop signs and stop lights.

I drive the car without much consideration of the bouncing ball but I am not gunning it at every light and I anticipate stops more than previous cars while driving in L.

I really wish there was a overall battery and efficiency rating that takes everything into account: acceleration, deceleration, temperature, humidity, parasitic power draws, altitude changes, passenger and cargo load, tire pressures, etc. The car literally has all of this information to do the calculations.

Really all I want to know (and I am sure others would be in this camp) is whether or not my battery and my drivetrain are as good as they can be.

If I have to drive like a dangerous granny getting in the way of progress and make myself late to get to the same mpg and mpc ratings as some of the people on here, I'd rather have less efficiency. But if something's wrong with my car, I want to get that addressed asap.

I am sure that GM is collecting all of this info and they have the calculations, but I am equally sure it would be a nightmare for GM if the common people had this information. They would be demanding expensive work under warranty because their car is slightly less efficient than the next guy's car due to inevitable manufacturing variances. It's a lot easier and cheaper for GM to handle those manufacturing discrepancies by just telling people it's their driving style.

As more Volts hit the road in my area, it will be interesting to go on drives with other Volts mimicking the exact same drive to compare efficiency. I would especially like to do that with people that are getting 50+mpc and 40+mpg.
 

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I am usually doing around 32mpg on ICE in Houston. Sometimes it's as high as 35mpg. I don't see how I could ever get over 40.
Interesting as I drive Beltway 8 every day and in the afternoon I'm running the ICE and routinely get 37 - 39 driving 70. The difference between 65 and 70 is negligible but at 60 the mileage actually seems to begin to drop somewhat. In town driving on ICE (<45) drops to your number of 32 - 35.
 

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FWIW, I drove Heights to Lovelady north of Huntsville and back (187 miles) on Saturday at 65-70+ mph (a bit faster on the way up as I was late). I burned through the charge at mile 34.5 but averaged 38mpg on in CS mode. Tires are inflated to 40 psi. I did not pre-condition (was running late and forgot) but it was not too hot when i left at 5:30 am so probably not big impact.

I've found that my initial charge indicator has dropped due to Summer heat from a range of 41 to a range of 35. I get a range of 38 driving up I45 to The Woodlands if I stay 60-65 but lose two miles or so when I am doing 70. The range killer for me is if I stop frequently to do errands and the car interior heats up. That initial A/C cool down really takes a toll on range if you do it 4-5 times.

The speed demon wife - sport mode with rabbit starts, I-10 at 70++ mph in early morning, with A/C in comfort mode ("it's my car and I can keep the temperature the way I like it") - is getting numbers almost identical to 692's. But if I drive her car on the weekend it goes back to being consistent with mine. So at least for us, it depends mostly on how we are driving. Best range numbers are just under 48 miles on a charge driving Heights to Woodlands but staying mostly on the feeder to max the range as a test.
 
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