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

Another point worth mentioning about heavier loads is that it increases the wear and tear on the equipment such as tires, brakes, shocks, leaf springs, air bags, the engine working harder to pull the weight, and so on. These, of course, are complicated to calculate.

I’ve been talking a lot about the effects of weight on the mpg, but the truth is I personally do not care at all about the weight of the load—at least for now, I should say. I’m too busy running the business to worry about small things like the weight. When I book a load, I care much more about the total amount I can gross per week. As I gain more experience, I’ll start paying more attention to other things like the weight of the loads. If I can generate the same weekly gross while booking lighter loads, then that would be a good bonus.

 

I also think, it is more important how the heavier weight is effecting the motor life span than the mpg.

It does effect the overall cost per mile in the long run.
You can still use the weight as a rate negotiation argument but to a rather small effect. I don't see a huge correlation between the load weight and its rate.
Reefers are hauling 30 50% heavier freight than dry vans but their better rates are deriving from the more specialized equipment than the weight itself.
Having said that, I remember that on my West cost runs (4200 - 4500 miles per trip) when loaded 20 k vs 45 k lbs meant a few hundred saved. Especially true, in 2008 - 2013 when fuel was quite often reaching 4 dollars per gallon.

 

@PE_Trans and @TallJoe good points about engine life. A useful thing to keep an eye on if you’re heavy a fair amount of time is the load percentage on your engine. The easier you get up to speed and the easier you drive it the lower that percentage and the better off you are. I doubt any of us here are driving like the cops are chasing us, but there is no doubt that wear items wear faster at heavier weights. But that all plays back to knowing your costs when you set a rate. For example, I should get 215k out of my drives, they’re wearing about 8500 miles per 32nd, and I know guys doing other stuff can see 400k. I just have to plan on tires every year and a half, it’s comes with doing what I do.

 

I get about 18 months on my drives also. Weighing 44k