Equation for determining gas mileage?

Discussion in 'Performance & Fuel' started by Silverado 2005 LS, Apr 10, 2013.

  1. Silverado 2005 LS

    Silverado 2005 LS New Member

    I know there's a way to calculate mpg through filling up and resetting trip then checking trip when you fill up next. But hat exactly do I gotta do? I just filled up. 21 gallons. And I reset my trip!
  2. dobey

    dobey Member

    Miles / Gallons = Miles per Gallon.
  3. stchman

    stchman New Member

    Miles driven / gallons used
  4. RayVoy

    RayVoy Active Member

    What the guys are saying, is fill tank, reset odometer (your here), drive until close to empty, fill and record gals to fill, divide the gals to fill into the miles driven.
  5. phoebeisis

    phoebeisis New Member

    Exactly-the main thing is make SURE you fill it COMPLETELY-
    OR at least fill it the same way-to one "click off" or two clicks.
    That is the trick-make sure it is filled the same way each time.
    Reset trip meter each time-
    divide miles by gallons M/G Miles per gallon literally means put miles traveled over gallons it took to travel that far-
    something like 255miles/21 gallons if it is city or maybe 350 miles/21 gallons
    Course you don't want to know you got 350 miles on 21 gallons you want
    to divide and get 16.66 mpg reasonable hy mpg if you have a heavy foot(say 75 mph or so if you have a 5.3 in your 2005 1/2 ton)
    Pure city maybe more like 11-14 mpg-short trips KILL mpg.
    Yeah just fill it completely-careful to not overfill-maybe 1 or two "stops pumping"-
    Luck
    Charlie
    PS I am a mpg nut-98 Suburban 2wd 2006 Prius
    the suburban gets an HONEST NO BS 21 mpg on long 3000 mile pure hy trips-set CC to 67 but obey all speed limits(45 mph hy work- 35mph in towns cities)-actual average trip driving speed probably 60-62mph- 21 mpg in an old Suburban 5.7 221,000 miles
    City mpg-different story-11-13 mpg-all wife's fault-she kills my mpg-if she didn't drive it I would get 14-16 mpg city(with effort-normal driving 12-13 mpg)
    Yeah 5200 lbs-no way around not great mpg-but your 5.3 is 1-2 mpg better than the 5.7.
  6. Silverado 2005 LS

    Silverado 2005 LS New Member

    Alrighty thanks for all the help guys ! Ill post up what mpg I get when I fill up next. Hope above 12right now but my diesel is killing my truck on mpg I'm sure(F250 7.3L turbo power stroke) gets 16town and around 18-20highway. I thought the truck was lying until I went and took down data and got a little less then what it was telling.
  7. STEPHENSON121588

    STEPHENSON121588 New Member


    I added larger wheels and tires on my truck and it threw the mph off which in turn threw the MPG and Odo miles counter off. If your speedo is off because of larger or smaller tires take a gps system and reset the trip on that. Just make sure its on everytime you drive.
  8. Pikey

    Pikey Moderator

    or use a programmer to correct the speedo for your new tires and rims! Larger tires will not only throw off your speedo but also computer controlled shift points will not be correct. Not to mention abs.
  9. STEPHENSON121588

    STEPHENSON121588 New Member


    Yep exactly!! I've been putting my extra $ to the side and waiting for my warranty to expire. Warranty just expired and now it time to find a good programmer. I started a thread about that in the performance section.
  10. phoebeisis

    phoebeisis New Member

    You can correct for taller tires wheels with some arithmetic
    Measure old tire height
    Measure new tire height
    Put new over old
    For example my 235/75 15 Suburban-tiny wheels tires just 28" tall-maybe 28.25
    More commonly 1/2 tons have 265/70 16-30.5" tall
    30.5/28.25=1.08
    Multiply that by your calculated mpg distance/gallons
    and you will get actual mpg
    Easier still just add 1 mpg city or 1.5 mpg Hy-to calculated mpg
    Those rule of thumb numbers 1mpg city 1.5 hy work OK for most reasonable size changes-2" increases
    If you went to 35" or 37" -well just do the arithmetic.

    Bigger wider tires increase aero drag and sometimes rolling resistance-
    the OEM engineers know what they are doing in respect to tire size
    Granted my TINY 235/75 15s look kinda funny now under a Suburban-yeah maybe they looked right in 1998-
    but they look like clown tires now!(but give great mpg-and oldsters like me-cheap wins over looks)
    Charlie
  11. shevy

    shevy New Member

    use more than 1 fillup

    Gas stations vary greatly in when the filler turns off, in other words some pumps let you put in more fuel than others which makes your calculation inaccurate.

    I would recommend using more than one fillup to calculate gas mileage. If you use 5 or more fillups (and corresponding miles) you get much better accuracy. Here is a link to example calculation:

    http://is.gd/nZ8nsI

    Good luck.
  12. kinson33

    kinson33 New Member

    And after you get you MPG calculated you can figure out how much you're spending for every mile you drive!

    Price per gallon / your mpg = how much you spend for every mile you drive!

    ex: My truck averages 14mpg. Price per gallon here currently is 3.39.

    3.39/14= .24

    So I spend roughly $.25 for every mile driven. Helps to plan for road trips :sign0023: :cool:
  13. phoebeisis

    phoebeisis New Member

    Last fillup my 1998 Suburban got GREAT city mpg
    411 miles/26.5 gallon=15.5mpg
    I drive exactly 6.2 miles one way to work the last 3 months-city but not too many stops
    most importantly my wife hasn't been killing my mpg with her 1-2 mile trips and long waits-motor on-at the bank etc.
    I motor on pulse and glide-but that is about it for mpg trickery.
    GM 1/2 tons have transmissions that glide in D as if they are in N when you lift off the gas-makes them great for mild hypermiling.
    Once I get in better financial shape I might upgrade to a 2004 5.3-to get better brakes and better mpg-and fewer miles-222,000 now.
    Yeah GM trucks can get pretty surprising city and hy mpg
    Charlie

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