Originally Posted by westernjeep401
For our second trip, the average speed was 51 mph, distance 220 miles, average miles-per-gallon 13.1.
I used cruise control about 65% of the trip. Oil life reduced from 55% to 51%. The rigs pulls and handles very well.
The order of importance for FE is:
Driver (skill, but better termed attitude, IMO)
Incorporating these tends to lend perspective. GCW, too.
Nice to see high numbers for a gasser. Was fillup at same pump?
FWIW I find that converting fuel cost to cents per mile to be the easiest way to understand long term trends.
58-mph/1,725-rpm is also my target speed. It is the highest FE speed. Up to 2k rpm is a well understood limit on a Cummins for economical operation, but from 60-mph on up the air resistance on any vehicle skyrockets. To 45 it is tire resistance (TT tires are 40% as with a tractor trailer) and from 60 it is the air. One can see why steering corrections are so important at either (and why we used to use 55 as a limit; its a heck of a sweet spot).
Trucks are geared for 55-65 operation. Not reliable above 65 due to risk
Have you changed out the antiroll bar bushings for polyurethane? KONI or Bilstein shocks another good idea.
Cummins and KW both advocate for a higher percentage of cruise control use. To deal with an aggressive CC I've learned to set it 1-2 mph lower so as to offset fuel burn in ascents in rolling terrain. MPG stays closer to that on level terrain.
Finally the easiest way to help truck aero is a bed half tonneau. From tailgat forward. Equalizes pressure on either side of tailgate. A piece of thin plywood would suffice, atop some of the gear
And although you didn't hear it from me, to keep MPG numbers highest don't fuel till at least thirty miles down the road preferably out of metro area traffic. (Best is at least fifty miles from city center to be away from regional delivery and commuters.) If your buddies filled the night before leaving home much the better. Refuel in the same way before another major metro.
While this doesn't change the annual average it sure as hell makes the highest mpg (highest mph steady state) with a pair of bragging rights fuel receipts.
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