Houston Road Trip
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Thread: Houston Road Trip

  1. #1

    Default Houston Road Trip

    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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  2. #2
    Join Date
    Jul 2008
    Location
    San Diego
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    8,701

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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.

  3. #3
    Join Date
    Apr 2011
    Location
    Wickenburg, AZ
    Posts
    540

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    Quote Originally Posted by DonC View Post
    humid air is less dense than dry air.
    Are you sure about this?

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  5. #4

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    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.

  6. #5

    Default

    Quote Originally Posted by AZ EV Driver View Post
    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

  7. #6
    Join Date
    Jan 2011
    Location
    Illinois
    Posts
    9,749

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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.
    Cyber Gray, Std Wheels, Black Leather/White Console, Park Assist. Picked up May 2011
    B3320
    Best All Electric Miles: 54.2
    Lifetime: 51,445 miles, 156 MPG, Remaining Oil Life 67%
    Typical Commute: 60 miles
    30 day Stats: 1375 miles, 250
    MPG, 96% Electric, 3% gas, Saved 61 gal., 26 kW-hr/100 miles
    VOLT TIPS & SECRETS Free Volt Manual here: Owners Manual (PDF)

  8. #7
    Join Date
    Apr 2011
    Location
    Livonia MI
    Posts
    872

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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.
    Last edited by Bob_Livonia; 07-13-2011 at 07:57 AM. Reason: Corrected typo

  9. #8
    Join Date
    Dec 2010
    Location
    Houston, TX
    Posts
    1,492

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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.
    -----------------------------------------------
    Volt #947 Delivered on 2/25/11 -- Sold!
    240V Blink Installed 10/28/11 -- Returned!

  10. #9
    Join Date
    Jun 2011
    Location
    Metro Detroit
    Posts
    114

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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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  12. #10
    Join Date
    Dec 2010
    Location
    Houston, TX
    Posts
    1,492

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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.
    Last edited by voltage692; 07-11-2011 at 11:32 AM. Reason: Nudity, language and adult situations
    -----------------------------------------------
    Volt #947 Delivered on 2/25/11 -- Sold!
    240V Blink Installed 10/28/11 -- Returned!

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