Just did a 500 mile round trip all lowland and without a MC trailer this time. 2005 Dodge 2500 long box with Grandby, 5.7 hemi, stock tires, loaded up with 1 person and 400lbs combined motorcycle and hitch carrier,
On my return trip frokm Hood River, OR to Seattle I got 14.5mpg indicated, 14.0mpg actual, averaging around 63mph. I experimented a bit with avg of 69mph and lost 1mpg. Elevations seal level to couple hundred feet the whole trip so fairly flat. This 14mpg figure was daytime with a 30 minute freeway stop and go in the middle of nowhere for unseen reasons.
When there was no wind driving at night down I-5 from Seattle, I was in the 15-16mpg area down to Vancouver WA. In the morning however the Columbia River wind tunnel east of Portland killed the great mileage numbers and ended up with 13, dropped like a rock into that headwind in I-84. This shows that like a large camper, It is the wind more than the weight that kills mileage. We do regular long trips in a diesel with a huge Bigfoot camper and tow 16 foot enclosed trailer. The trailer comes along practically for free. The camper blocks all the wind. I sometimes think about fabricating front and side fiberglas cowlings and wonder how much that would help (vs the cost and effort). Would fasten to the camper front and also to the front jackstand brackets, 3 pieces total. I do about 8K miles per year.
