What is the difference between a 40,000lbs load, a 44k lb load, and a 46k? In MPG?

Discussion in 'Ask An Owner Operator' started by RoadRunner36, Jan 19, 2020.

  1. RoadRunner36

    RoadRunner36 Bobtail Member

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    Dec 26, 2019
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    Im trying to find some information on the differences in these upper end of the legal weight limits.

    It seems like there is some signifigant bell curve when measuring MPG based on load weight, that starts to dip sharply around 44000, and more sharply at 45,500...

    Considering my truck weighs 33,500 empty trailer and full tanks, and gets about 6.3 MPG overall. What kind of effects on my MPG could these varying weights have.

    Lets say
    40000
    41000
    42000
    43000
    44000
    45000
    46000

    Lets say flat roads mostly.

    Is there a curve? Does anyone know how to calculate the differences?

    Feel free to apply an est MPG on each weight, or create an answer that does not necessarily fill in the blanks. Im open to any answer that lights the way
     
  2. TallJoe

    TallJoe Road Train Member

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    Flat:

    40000 : 6.7
    41000 : 6.7
    42000: 6.6
    43000: 6:6
    44000 6.5
    45000 6.4
    46000 6.3

    hills

    40000 : 6.3
    41000 : 6.3
    42000: 6.2
    43000: 6:2
    44000 6.0
    45000 5.9
    46000 5.4
     
  3. Dale thompson

    Dale thompson Heavy Load Member

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    commerce twp,mi
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    Given the minimum information I think TallJoe has a estimate that I would totally agree with.
     
  4. Milr72

    Milr72 Medium Load Member

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    Dec 16, 2011
    S W Missouri
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    The real question should be is how much more does the 46,000 pound load pay versus the 44,000 or the 40,000 pound load. The extra weight should pay a lot more than what the additional fuel cost would be.
     
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  5. snowwy

    snowwy Road Train Member

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    Jul 6, 2009
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    Too many variables to possibly have an answer.

    You can run the same load on the same route with the same weather conditions fueling up at the same station and have up to a 1 mpg difference.

    Fuel quality is never the same from day to day.
    And I've seen a 1 mile difference in the mountains.
     
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  6. RStewart

    RStewart Road Train Member

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    Norman, OK
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    With my truck there isn't much different between 40k and 44k on flat ground. In the hills it will be a little different but how big the hills are and how many they're are will determine tree difference. Worst case scenario, maybe half a mile per gallon. Driver has a big impact on this as well.
     
  7. x1Heavy

    x1Heavy Road Train Member

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    Mar 5, 2016
    White County, Arkansas
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    You are going to burn more fuel to lift a heavier load over a mountain.

    However.

    You open a can of worms with that question. For example I had a older big cam pulling townhill near Breezewood at 80000 at 19 mph or so upgrade. Thats depending on temperature and humidity situation. If shes frisky she will run that at 21. It's 5 mile pull. It was a fuller 10 I believe and other standard late 87's era truck hardware.

    Not long after later that year company gave me a virgin mack day cab with a 350 and a significantly different set up. Fuel capacity was no where near as much and I did the same hill, same load with the same shipper at 45 mph. It did not take very long to lift that up and over. And more or less we managed to not need to carry so many gallons to get a days work in. Although refueling was possible if running 4th load on that flatbed for that workday.

    Most of my past 10 tractors or so, all of them were relatively modern. And did not "act loaded" until there was a certain amount in that trailer. For some of those tractors they LIKED to be loaded. Others with less than ideal engines (Particularly if employer relies on the smallest, least HP engines) they will drink gallons trying to run a hill. And some areas of the USA like western Kansas is one big upgrade from Kansas City towards Denver (A mile up) and fuel is out the window some days.

    I can go on. But as a rule of thumb for a 515+ detriot or similar for the 2000 era I expect a minimum of 1650 working miles before fueling. As a team we go through 10 gallons a hour and refuel every 30 hours give or take on average. That works out very close to what the tractor would be reporting to us around 6.8 loaded. Better than that empty. And we could some days trust it to get us 2100 miles if necessary. (And did once or twice, it's a gamble)
     
  8. PE_Trans

    PE_Trans Road Train Member

    Assumption:

    80k max gross weight
    7.0 mpg at 62 mph

    35k (empty weight with reefer trailer)
    9.5 mpg at 62 mph

    80k (gross) - 35k (empty) = 45k (max load weight with reefer trailer)

    Calculations:

    0k (empty) (0%)
    9.5 mpg at 62 mph

    11.25k (load weight on reefer trailer) (25% of max load weight)
    8.88 mpg

    22.5k (load weight) (50%)
    8.25 mpg

    33.75k (load weight) (75%)
    7.63 mpg

    45k (load weight) (100%)
    7.0 mpg
     
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  9. Long FLD

    Long FLD Road Train Member

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    Murdo SD
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    Unless you’re loading at the same place and going to the same place there are way too many variables to measure the difference between 6k of weight.
     
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  10. mpd240

    mpd240 Heavy Load Member

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    Minnesota
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    Flatbed. Wind resistance seemed to make the greatest impact for me.
     
    Coffey Thanks this.
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