What kind of accuracy are people seeing on the trucks calculations of MPG vs. Pen & paper recording of filling up at the pump and mileage driven?

I ask because I've been getting such un-impressive mileage based on the lie-ometer, I finally calculated it the old fashioned way expecting to get better results, and they were significantly worse!

Trucks numbers:
370 miles driven, 25.5 gallons used for 14.5MPG

Realtime numbers:
370 miles driven after full tank, 29 gallons to fill again for 12.7mpg! WTF!

Granted I'm running 35's and a 2.5" level but 12.7 out of a 3.5 EB come on!

This is on my daily commute to work not hauling anything but myself. 3 miles down the hill at 60mph, 1.5 miles through town at 40mph with no stops, then another 14 miles on the interstate at 75mph, and the same in reverse order coming home.

 

double posted admin please delete.

 

No idea how that happened.

 

My truck says I'm usually getting 2mph better than I usually am.
Truck roughly around 19.5
Fuelly says around 17.5 each time

 

Mine is off by 6%, checked multiple times. Many threads, most have the same observation.

 

Yep, off by ~6% for me. Typically 20-22.5 MPG hand calculated versus computer showing 21.5-24 MPG.

 

That sounds about right for a lifted truck on 35s for mixed city/highway driving to me.

If you do a highway only road trip what do you get? 15-16?

 

Go from 75 to 68, set the cruise, and see what happens.

 

We're not discussing how to get better MPG, we're discussing the trip computer calculation vs the true hand calculation. The trip computer under reports gallons used by 6%, thereby overreporting MPG by 6%.

 

I logged 8 consecutive tanks, 227 gallons, and the lie-o-meter's reported gallons used was low (and mpg calculated from same was high) by 5 to 9 percent per tank with an average error of 6.5 percent.

Even correcting for the reporting error it's still doing better than I'd expected.