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Thread: How reliable is the mpg display?

  1. #1
    Registered User Guenther's Avatar
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    How reliable is the mpg display?

    I am still learning my new F700GS.

    I tried to use the trip odometer (which is off low by 2% according to my GPS) and the amount of gas needed to fill her up to calculate the mpg. But it varies because I can't reliably fill up to the same level every time.

    How reliable is the mpg value displayed from your experience?

    How high do you fill up anyway - close to the top?

    /Guenther
    1989 R100GS, 2017 F700GS

  2. #2
    Fortis Fortuna Adiuvat Omega Man's Avatar
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    On my F800GS, which is pretty similar I think, Im careful not to overfill. Im pretty sure overfilling gets into the vapor recovery system and a steady diet of VR saturation most likely not do any good. My mileage seems to be around 52 mpg and I know that around 160 miles its gas stop time.
    OM
    "You can do good or you can do well. Sooner or later they make you choose." MI5
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  3. #3
    Registered User Guenther's Avatar
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    Im careful not to overfill.
    OK, but to which point in the filling snorkel?

    A friend of mine with a F800GS always fills up to one inch below the lid for over 8 years without a problem.

    around 52 mpg
    Does the '~52' on the computer match with what you actually get?

    /Guenther
    1989 R100GS, 2017 F700GS

  4. #4
    Fortis Fortuna Adiuvat Omega Man's Avatar
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    Im actually not so fussy on the fill line. The gas fill is on the right side meaning its pretty full when upright. I did the math a couple of times and was satisfied and basically know where I am at via the trip meter gas wise.........I have never had a vehicles computer match doing the actual math
    OM
    "You can do good or you can do well. Sooner or later they make you choose." MI5
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    2009 F800GS 1994 TW200

  5. #5
    Registered User WalterK75's Avatar
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    Keep careful records of the amount of gas purchased and distance traveled. Calculate the mpg. If you do this over a long enough period you will get a fairly accurate result. The few ounces over or under from one filling to the next will cancel out.
    Walter

    Every decent man is ashamed of the government he lives under.
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  6. #6
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    My F-twin is spot-on with the fuel mileage displayed when compared to my doing the math manually. For the first three/four years of riding the F-twin I was anal about tracking my fuel mileage: it got such good mileage (55+mpg on most roads at most speeds) that I did not believe it. Finally I was convinced and not I do not even bother to keep track manually any longer, I simply trust--and depend on--the fuel mileage displayed on the dash.

    Good luck.
    Royce
    On the coast of Kansas
    2012 F800ST

  7. #7
    Kawa Afterthought weschmann's Avatar
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    Quote Originally Posted by Guenther View Post
    OK, but to which point in the filling snorkel?

    A friend of mine with a F800GS always fills up to one inch below the lid for over 8 years without a problem.



    Does the '~52' on the computer match with what you actually get?

    /Guenther
    Of the 62000 miles I put on my 700, I always filled up to almost overflowing. Never had a problem. And I found the tate to be pretty much spot on, with usually a half gallon left when the counter started climbing. Before I leave nestled an extra camel fuel rank I could get 180 miles per tank n combined speeds as long as I stayed at 70 Mph or less. At 80 Mph my range dropped to 140 miles per tank.

  8. #8
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    A couple of years ago, I started across a stretch of desert without thinking through the gas situation. About 20 km into the crossing, I realized I had 130 km of desert to the next gas station and the range readout said 150 km so I decided to keep going rather than backtrack. Keeping a close eye on the range reading, I soon realized that it was going down faster than the distance-remaining-to-gas. It looked like I might not make it. I pulled up tight behind a truck and drafted for about 80 km. This cut my fuel usage in half and I made it easily to the gas station. The road was two lane with no side roads or crossing roads and almost no traffic, so it felt pretty safe drafting on the truck, normally a very risky behavior. But it was far from an ideal solution. Ever since then I have been very conservative in refueling and rarely let the gauge drop below half a tank or 200 km remaining.
    Will
    MOA #2607 - 2015 R1200R Cordoba Blue
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  9. #9
    Registered User mylanc's Avatar
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    Quote Originally Posted by royce View Post
    My F-twin is spot-on with the fuel mileage displayed when compared to my doing the math manually. For the first three/four years of riding the F-twin I was anal about tracking my fuel mileage: it got such good mileage (55+mpg on most roads at most speeds) that I did not believe it. Finally I was convinced and not I do not even bother to keep track manually any longer, I simply trust--and depend on--the fuel mileage displayed on the dash.

    Good luck.
    +1
    2012 F650GS

  10. #10
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    I find it varies, and I'm not sure why.

    In the spreadsheet below, a couple columns may need some explanation.
    • MPG - This is the calculated MPG based on miles and gallons used.
    • MPG Readout - This is the indicated MPG.
    • Delta - This is the difference between the two.



    Elnathan's Mileage.xlsx - Excel.jpg

    As you can see in this screen shot, it varies from -10 to +5. Some of that may be because I was riding into some strong head and cross winds, and at speeds of around 75 mph.

    I keep track of my MPG readout as I go along and the miles traveled as I'm riding. And I plan for a gas stop at about 160-180 miles.

    Chris
    Elnathan - 2014 BMW F800GT
    IBA# 49894 True Rounder = 0-20's - Rounder -- to -- 100's+ Red Hot Rounder
    John 14:6

  11. #11
    Registered User Guenther's Avatar
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    Chris, that is an excellent data collection!

    A crucial part of the gallons added is to always stop filling at the same tank level. How high do you fill up? To the bottom of that plastic pipe?

    /Guenther
    1989 R100GS, 2017 F700GS

  12. #12
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    I fill to about an inch and a half from the top of the filler neck.

    Chris
    Elnathan - 2014 BMW F800GT
    IBA# 49894 True Rounder = 0-20's - Rounder -- to -- 100's+ Red Hot Rounder
    John 14:6

  13. #13
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    Quote Originally Posted by daboo View Post
    I fill to about an inch and a half from the top of the filler neck.

    Chris
    That single word is the problem with manual calculations of mpg. It is almost impossible to get the precise amount of fuel into the tank each time we fill up. Hence, I now go with the display on the dash of my bike. I figure the computer can accurately calculate the fuel used, not the fuel added to the tank each time.

    Good luck.
    Royce
    On the coast of Kansas
    2012 F800ST

  14. #14
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    The "about" isn't referring to an inch and a half of variance. It' just that I haven't put a tape measure into the filler opening to measure how exact the distance is. I make every possible effort to fill up to the same point each time.

    My desire to track the variance in the actual calculated MPG verses the displayed MPG is simply to get a feel for how close that display is. When I'm out on a trip on some empty roads out west, I want to get a feeling of how far my range is under the conditions I'm riding. The display is close...but not exact. The only exact calculation you'll find, is by manually computing the MPG...but only if you fill up to the same point each time. But even if you're off by two tablespoons...it isn't enough to make a difference.

    Chris
    Elnathan - 2014 BMW F800GT
    IBA# 49894 True Rounder = 0-20's - Rounder -- to -- 100's+ Red Hot Rounder
    John 14:6

  15. #15
    I fill to the bottom of the neck, as recommended in my manuals for my K1200GT and R1200GS. Same place every time. Bottom of the neck.
    The lion does not even bother to turn his head when he hears the small dog barking.

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