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

That’s good in theory but it won’t work like that in reality. You can’t base it off a long running average for mpg and then say what your fuel cost will do based on percentage of your max load. The load isn’t on your truck long enough to skew numbers one way or another. On an average day under normal conditions a 45k load from Denver to KC is going to see higher mpg numbers than a 40k load from KC to Denver.

 

I am aware it won’t work “exactly” like that. The mathematical theory is, however, correct assuming the conditions (roads, weather, etc.) are the same. This data is useful if you can select loads, and you are comparing multiple loads on a particular lane. It’s unfortunate when people don’t understand the value of the formulas I posted.

 

All I’m saying is that just because a load going from A to B is 4K lighter than another load going from A to B it doesn’t mean you will save a certain amount on fuel based on your percentages. I get what you’re saying and I understand how you came up with it. I can go back and get my fuel numbers on the exact same 48k load going to the exact same place and I would venture I’ll have over 1 mpg difference from my high to my low, maybe almost 2 mpg. And I can look and find a light load or two also. I agree with your percentages in theory, I don’t feel the dollar amounts are useful because on any given day your mileage will swing from your long term average for any number of reasons.

I spent $64781.22 on fuel for 2019. Our outbound loads are 48k and return loads are 50k. Taking the fact that we get paid by the ton on our return load out of the picture, I doubt I would see a noticeable difference in fuel cost if I hauled 2k less on all my return loads.

 

It is obviously a guess game but with enough time everyone should know, or feel, his engine's mpg output depending on weight. With the ECM output instant display, you can make various tests under different circumstances. They are, of course, only ECM calculations but I think they do adhere well enough to reality or you can post adjust the readings, if you notice bigger discrepancies.
All other factors are important too; notably fuel quality and weather conditions but they don't effect the impact of different weight values on their corresponding mpgs.

For me, when selecting a load, the weight is frankly the last thing to consider unless over 45K lbs on a long haul and I have to beat hills with that. I don't mind 40K lbs and plus loads this time of a year.

 

A small number like 1,000 lbs won’t disappear into thin air. It doesn’t work that way. The number is just too small to notice it on 500 miles. You would need to run many thousands of miles for it to become visible. Just imagine the implications if the 1,000 lbs meant nothing to your mpg. To be clear, I am referring to identical trucks and weights running the same lanes.

 

And if you have to run many thousands of miles there are 100 others things that will affect mpg’s one way or another during those trips, thus not being able to pinpoint the mpg gain or loss due to load weight. The conditions will never be identical other than the weight of the load.

 

48k load from Hutchinson KS to Cedar Rapids IA. I don’t keep notes on the weather because I have to get there no matter what. But I pull the same trailer all the time and I run 63-65 religiously.

12/8 I got 6.02
12/29 I got 6.42
1/7 I got 6.85

If I’m seeing .83 difference on the same load you’re not going to convince me you’ll see a difference based solely on load weight between the 3 weights the OP asked about.

 

Yes but the impact of the load weight is the same. The difference has to do with with the weather conditions such as wind, slippery or wet road and perhaps better or worse fuel quality. We are trying to isolate the impact of the weight only on mpg.

 

You forget fuel quality

 

And I’m saying that it’s not going to be possible to isolate it to load weight only because there are too many other variables. You would literally have to drive thousands of miles on a test track under clear and sunny conditions with no wind. In the real world it’s not happening, let alone trying to figure out the impact of a few thousand pounds of cargo weight.