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Thread: How can I calculate my gas mileage?

  1. #1
    Ridin Dirty dom's Avatar
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    Question How can I calculate my gas mileage?

    How can I calculate my gas mileage and what is a normal gas mileage?

    What could cause gas mileage to go up or down?

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  2. #2
    Senior Member grouch's Avatar
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    Quote Originally Posted by dom View Post
    How can I calculate my gas mileage and what is a normal gas mileage?

    What could cause gas mileage to go up or down?

    Just figure how many miles you drove, fill up all the way and divide the miles by the gallons. I generally use my trip odometer to figure my mileage. I also keep a small calculator in each vehicle.

    What is normal? The only way to figure that is to keep track over time. As for what will make it go up and down, that is mostly driving type and style. Hammer on the throttle and your mileage will tank. In town driving is lower than highway. You'll usually get your best mielage on the state highways around 55-60 mph. You will get less on the interstate at 70 due to increased widn resistance.

    Let the mechanical condition drop, so will your mileage. Frotn end out of alignment, worn spark plugs, dirty air filter, low tire pressure, restricted exhaust and so on will make you use more fuel. You could write an entire chapter in a book about fuel mileage and not even scratch the surface.
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    I have often heard that driving 55-60 mph saves gas compared with 70 mph or more. I have never been able to test that theory, however. Driving 55-60 mph is simply not an option for me as it is boring and below the normal speed for driving, even on state highways.

    I have calculated gas mileage in my various cars over the years. I have found that gas mileage does NOT drop considerably between 65 and 80 or even 85 mph at least in my vehicles. That may have to do with operating your engine at close to the torque peak. The increased thermal efficiency at higher rpms makes up for some of the increase in wind resistance.

    For instance, in my Saturn, driving 70 mph, I get around 29 mpg. At 80-85 mph cruise speeds, it is 27.5-28.0 mpg. Hence, driving 80-85 makes a hell of a lot more sense to me if I can avoid the tickets.

    In addition to speed, there are other factors that influence gas mileage. I have found that the greatest factors are air temperature and use of A/C in the summer.

    A friend of mine did a test at different speeds and A/C uses and found that his mileage dropped by 4 mpg using A/C. That is the equivalent difference in gas mileage between driving 55 and 75 mph in his car. It was a 2006 Kia Sprotage V6.

    Air temperature can drop your gas mileage by 1 or 2 mpg, as colder air is more dense, throwing more fuel in your engine.

    Tire pressure is also an influence. Improperly inflated tires can drop your mileage by 1 mpg as well.
    Last edited by swamprat; 12-07-2010 at 09:09 AM.

  4. #4
    Administrator Ken's Avatar
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    Quote Originally Posted by dom View Post
    How can I calculate my gas mileage and what is a normal gas mileage?

    What could cause gas mileage to go up or down?
    I have an Excel Spreadsheet I wrote a few years back - and still use - that gives me a full analysis of dates, petrol costs, mileage, mpg, mpliter etc. I tried to post a sample but unfortunately it will not hold its format so I had to delete it. If you have Excel I could try to email it to you.

    Ken.
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  5. #5
    Ridin Dirty dom's Avatar
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    Hi Ken.

    Can you try to upload it again?

    I added .xls to allowable format types.

    I need to add the new excel format too.

    Excel sheet upload test post.
    Attached Files Attached Files

    "Tutto nello Stato, niente al di fuori dello Stato, nulla contro lo Stato "
    -Mussolini
    All within the state, nothing outside the state, nothing against the state.

  6. #6
    Administrator Ken's Avatar
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    Quote Originally Posted by dom View Post
    Hi Ken.

    Can you try to upload it again?

    I added .xls to allowable format types.

    I need to add the new excel format too.

    Excel sheet upload test post.
    Here we go. It looks OK in preview - I have cut off the last column which merely identifies all major journeys made during the period between fill-ups.

    Ken.

    Date
    Miles
    Cost ()
    Cost/Ltr
    Litres
    Miles/Ltr
    /Gall
    Gall's
    MPG
    Cost/mile
    02-01-10
    402
    53.00
    110.90
    47.79
    50
    5.09
    32.78
    16.77

    No, that didn't work, will think again.

    Ken.
    Last edited by Ken; 12-08-2010 at 07:18 AM. Reason: Failed copy/paste of spreadsheet.
    Die dulci fruimini!
    Ken.
    Wolds Bikers, Lincolnshire, England.

  7. #7
    Administrator Ken's Avatar
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    Quote Originally Posted by dom View Post
    Hi Ken.

    Can you try to upload it again?

    I added .xls to allowable format types.

    I need to add the new excel format too.

    Excel sheet upload test post.
    Trying as an upload rather than a cut/paste.

    Ken.
    Attached Files Attached Files
    Die dulci fruimini!
    Ken.
    Wolds Bikers, Lincolnshire, England.

  8. #8
    Ridin Dirty dom's Avatar
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    Upload worked!

    Sweet. I'll check it out in a bit.

    "Tutto nello Stato, niente al di fuori dello Stato, nulla contro lo Stato "
    -Mussolini
    All within the state, nothing outside the state, nothing against the state.

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