I agree with Tom. Your criuse speed has a lot to do with your fuel economy. The wind is beyond your control.
We are running a Country Coach powered with a Cummins ISX 600-1850 lb.ft. torque and weighing in at 51,000+ on the 'CAT' scales at the travel center with full fuel and water.
We tow a Saturn Vue most of the time. I found that running at 68-70 mph on the highway was delivering me 6.5-6.8 mph on average.
A head wind is a curse! It can rob you of another 10-15% of your economy at almost any speed. It does seem that life is a head wind mose of the time.
We decided that we would slow down a little and attempt to save some money by cutting our criuse speed to 63-64 mph on those long runs.
Well, we are now enjoying 7.3-7.6 mpg now on a regular basis.
That big flat front on our coach really plows thru the air like a brick. The higher our speed the more wind resistance created.
We take a little bit longer to get to our destination but it is worth it. With diesel over $5.00/gal last year we learned a good lession. $.70c a mile just for fuel wasn't any fun. besides, in the scary event of a front tire blow out, controlling the wagon is a bit easier at 60 that at 70.
Bill Herring
F122708
2008 Country Coach Affinity
ISX600/Allison MH4000
Naples, Fl.
Toad-Saturn Vue
