Closing the Gap: How much does it matter?

Yes the gap makes a difference, If you don't have them yet might want to put some Airtabs on to. Thy definitely help to get that air flow around the trailer and give you better stability in the wind.

 

your trailer will make the biggest difference. that air hitting the tandems.

 

My computer on 1999 Detroit engine also shows 9.4-9.8 mpg, does not mean it's true. Do you fill up the tanks all the way, then divide miles driven by gallons used?

 

To many variables, there would be no way to do that with ant accuracy, Even if you had the exact same route every day things are always changing like the weather. Do you keep a 30,60,90 day average for your truck? In general the airtabs should get you 1-3ths

 

Now I know y'all like to hate on kevin Rutherford, but theres an app called "fuel gauges" just search for let's truck in app store or google play.

Literally 10 seconds to add a fuel entry and keeps track for any duration averages you like.

My REAL numbers are always BETTER than what the ecm estimates

 

Old tech that's the same "new tech" being done by a computer. It's nothing special. It's simple math a mind is a terrible thing to waste. I try to exercise mine often. Your truck is more accurate how did you check the accuracy?