How much mpg is lost running a mid-roof instead of high-rise pulling a van?

I had a w900L flat top in 2013.The best I could do was on average 5.5 a mile for a month with the van. I also pulled a step deck trailer I could constantly stay over 6.5 I actually could average 6.8 for a month with the step.

 

Lots and lots..and….how bad can it be?

I just shut down early for the day I-80 west of Chicago about 50 miles or so.

Head wind of 25 mph I was per dash getting 4.3 mpg.. I was only limping along at 65mph..@80k gross.

Last trip WA to Buffalo, NY I got 6mpg with a mild tail wind.. The 6mpg was only acquired because I forced myself to run the entire trip slow. Yes I ran 67mph across SD , was difficult for me to do and it’ll never happen again

389 mid-roof with dry van. Cummins 565hp with 3:55 axle ratio.. Set up for mountain driving with heavy loads..

Quarterly ifta reports show an average of 5.20 mpg. I only idle when I have to

 

Just put a wing on top.

Same difference.

 

I know when I ran a cascadia day cab it was at least 1 mpg worse than a cascadia sleeper.

However also note I put a turbo roof wing on my 379 and only gained like .3mpg.

 

Also depends on the bunk to trailer gap. If you get it sucked up tight enough your brick in the wind will be smaller..

Truck models will make a difference as well. A FLD mid roof only stands about 10' tall, whereas a Crapcadia or 9400 Binder will be 11' tall..

What kind of mid roof?
A hood, or curb sniffer..

Could also put a small wing on the tractor roof,
or a nose bubble on the wagon to help some..

Edit
Guess I type slow.. lol

 

What is your fuel cost as % of profit, Or - cents per mile in your operation ?

 

Adding a turbo wing, small one on a mid roof, or large one on a flat top, usually good for 1/3 to 1/2 mpg increase.

 

Unless you are hauling your own freight, If the difference in mpg is going to effect your bottom line that much you might want to rethink your plan all together.

Also there is no reason to spend all that money on a truck that you hate walking out to every day

5.41 last quarter at 80k…ish, with a 285” wheel base and a modular stand up in New England/north east