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MPG Drop

Discussion in 'Performance and Tuning' started by jdavenport, May 8, 2018.

  1. May 8, 2018 at 7:58 AM
    #1
    jdavenport

    jdavenport [OP] New Member

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    I averaged about 13.5 mpg between city and highway driving before leveling my truck and changing the wheel and tires. After I installed king OEMs and 17" rims with a 315 70 17 MT I dropped to 7.5MPG. A drop of 6.5MPGs seems extreme? Is there anything I might have missed that is contributing to to my awful MPGs?
     
  2. May 8, 2018 at 8:01 AM
    #2
    T-Rex266

    T-Rex266 Independentoffroad who? That's cute. Staff Member

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    How are you calculating this?
     
  3. May 8, 2018 at 8:03 AM
    #3
    jdavenport

    jdavenport [OP] New Member

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    Miles driven / size of the gas tank. For example hundred sixty miles divided by 21 gallons is approximately 7.6 MPG.
     
  4. May 8, 2018 at 8:05 AM
    #4
    ChrisTRDPro

    ChrisTRDPro New Member

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    Very low tire pressures?
     
  5. May 8, 2018 at 8:15 AM
    #5
    k9shag

    k9shag New Member

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    I fill the tank, and reset the trip odometer. The next time I fill up I divide the number of gallons I jut put in by the number of miles driven since the last fill up. This will get you really close to actual mpg, and will be different from the onboard mpg computer.
     
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  6. May 8, 2018 at 8:15 AM
    #6
    Cement Pro

    Cement Pro New Member

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    Speedo recalibration
     
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  7. May 8, 2018 at 8:16 AM
    #7
    jdavenport

    jdavenport [OP] New Member

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    That's how I do it.
     
  8. May 8, 2018 at 8:19 AM
    #8
    jdavenport

    jdavenport [OP] New Member

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    Shouldn't be significantly low about 35 PSI if I remember correct
     
  9. May 8, 2018 at 8:20 AM
    #9
    jdavenport

    jdavenport [OP] New Member

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    I know the spedometer would be off after changing tires and the odometer wouldn't read 100% accurate but I didn't think that it would result in that significant of an trip odometer reading.
     
  10. May 8, 2018 at 8:21 AM
    #10
    k9shag

    k9shag New Member

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    Ok, well Cement Pro may be right on the recalibration though it still seems like a huge drop
     
  11. May 8, 2018 at 8:26 AM
    #11
    4Runner

    4Runner New Member

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    Does this thing work?
     
  12. May 8, 2018 at 8:29 AM
    #12
    jdavenport

    jdavenport [OP] New Member

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    I hope that's it but I have my doubts considering I went from a 32 inch to a 34 inch tire it doesn't seem like it would warrant that kind of drop.
     
  13. May 8, 2018 at 8:49 AM
    #13
    joonbug

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    The speedo difference only makes like .5 mpgs difference. It’s not that. Why are you dividing by the size of the tank? Are you running it all the way down to 0 miles left and refilling 21 whole gallons?
     
  14. May 8, 2018 at 8:52 AM
    #14
    mtTundra

    mtTundra New Member

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    Longer list than the wife needs to know about....
    You are traveling further than indicated so you may need to manually calculate your distance traveled.
    As other said a speedo healer could solve this part of your equation.
     
  15. May 8, 2018 at 8:53 AM
    #15
    parker44

    parker44 New Member

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    That seems like an excessive drop for sure.
     
  16. May 8, 2018 at 10:26 AM
    #16
    jdavenport

    jdavenport [OP] New Member

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    21 gallon gas tank. Used 1/4 so 5.25 gallons, divided by 40 miles driven. 7.6 MPGs.
     
  17. May 8, 2018 at 10:31 AM
    #17
    jdavenport

    jdavenport [OP] New Member

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    That's what I figured. I assumed I would see a 2 MPG drop.
     
  18. May 8, 2018 at 10:31 AM
    #18
    TheBeast

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    try with 40psi + on each tire.
    I run KINGs and 295/70/18 Toyo A/T (41 psi) and my average is 14 mpg.
     
  19. May 8, 2018 at 10:32 AM
    #19
    jdavenport

    jdavenport [OP] New Member

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    I'll give it a shot thanks! I know the MT will redcue it more but I wouldn't think that much more.
     
  20. May 8, 2018 at 10:35 AM
    #20
    Pudge

    Pudge Super Secret Elite Member #7

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    You need to divide mikes driven (corrected for tire size/ odometer being off) by how many gallons your tank. Guessing 21 or portions of a full tank isn't accurate.
    I would imagine you'd lose a few MPG but not almost half. That's crazy
     
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  21. May 8, 2018 at 10:35 AM
    #21
    joonbug

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    So you're estimating how much gas you used? That is very inaccurate. You need to do it the way @k9shag recommended, and get a larger sample size. Like maybe the whole tank. Fill up, zero the odometer, use most of the tank, then get an accurate amount of gas used by seeing how much gas goes in on next fill up.
     
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  22. May 8, 2018 at 10:39 AM
    #22
    jdavenport

    jdavenport [OP] New Member

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    It's a fresh trip odometer. And as far as the accuarcy of estimated gas used I know it's not 100% but I frequently montiored my MPGs even prior to putting the lift on and what it read at 1/4 would be very close to the final tank. I'll see how it goes until I put the gas in and get a final number to get a 100% accurate calculation.
     
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  23. May 8, 2018 at 10:42 AM
    #23
    parker44

    parker44 New Member

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    To go along with the post above, if I'm not mistaken, these are actually 26 gallon tanks. At least on my truck, my owners manual says it's a 26 gallon tank, however I have had the gas light come on and it takes less than 20 gallons to fill up. Now I'm not much on pushing my luck to test it, but I've read elsewhere that these trucks have large reserves. It sounds like though that your calculations are off. Use the number of gallons you put back in the truck at the pump as how much was used.
     
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  24. May 8, 2018 at 10:44 AM
    #24
    Atomic City Tundra

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    The hash marks on the gauge aren't going to give you an accurate reading at all. Plus, when did they start making a 21 gallon tank? Mine is 26. I know the newer ones have a 38 gallon option, but I am not aware of a 21 gallon option.

    Best bet is to actually see how many gallons you put in at the pump. Use that number for your calculation.
     
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  25. May 8, 2018 at 10:44 AM
    #25
    14burrito

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    You need to run real numbers on your math, not guestimates.

    Fuel, reset trip, drive, fuel - then do the math. Don't guess.
     
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  26. May 8, 2018 at 10:49 AM
    #26
    jdavenport

    jdavenport [OP] New Member

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    I know the tank contains 26 gallons, but each fill up is 20-21 after the light comes on. Again I know it's an estimated number, but it's fairly accurate from what I've experienced in my truck this far.
     
  27. May 8, 2018 at 10:51 AM
    #27
    jdavenport

    jdavenport [OP] New Member

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    They're 26 but the light comes on at 20 meaning they count 6 gallons as reserve and not really factored into the gauge.
     
  28. May 8, 2018 at 10:53 AM
    #28
    jdavenport

    jdavenport [OP] New Member

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    Thanks for the replies and help everyone. I'll know for sure when it's time to refuel, but i just wanted to see if anyone else was in this area of MPGs.
     
  29. May 8, 2018 at 11:06 AM
    #29
    TheBeast

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    the thing is that he used the same mpg calculation method and now he finds a lot lower. maybe a bad batch of gas ? was it just one fill up or has it been the same for couple tanks already ?
     
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  30. May 8, 2018 at 11:08 AM
    #30
    jdavenport

    jdavenport [OP] New Member

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    This is the first fill up and one of the only times at a 76 station I thought that might be it.
     

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