Equation for determining gas mileage?

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

  1. 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 Epic Member 5+ Years 500 Posts

    Miles / Gallons = Miles per Gallon.
  3. stchman

    stchman Active Member 2 Years 1000 Posts

    Miles driven / gallons used
  4. RayVoy

    RayVoy Epic Member 5+ Years 5000 Posts

    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 Epic Member 5+ Years 1000 Posts

    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"-
    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. 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 Staff Member 5+ Years ROTM Winner 5000 Posts

    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 Epic Member 5+ Years 1000 Posts

    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
    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)

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