My Super Duty Diesel gets 12.5 towing my enclosed trailer with the show car in it, and 18.5 to 20.0 not towing, depending on how fast I go (68-80 MPH). I tow about 50% of the time, and most trips in this truck are 1,000 to 3,000 miles each. I do not drive this truck around town, or for errands or daily usage. If I start it, the next stop is usually a few hundred miles away.
In my case, I use the notes to distinguish towing or not towing. It works well because my trips are such long duration. Usually at least a couple of tank fulls. Looking at the graphs and MPG in the log it's easy for me to see towing or not towing.
I don't think many people look at other peeps mileage and make comparisons. I don't, too many variables and unknowns. Most people ignore odometer error. I don't. Hondas for years read 8% over actual miles traveled. 30MPG calculated using odometer reading, was really 27.6 MPG. An example of why comparisons can be misleading. So stipulating tow and no-tow might be an explanation for large swings in MPG, but really, who cares other than the owner? Use the note field as a reminder to yourself that the low MPG periods were from towing activities.
In my truck's profile, I recently added a note regarding the two MPG's it gets towing or not-towing. After 22,500 miles in 18 months, I've got my mileage expectations pretty dialed-in, and the readings are usually within 5% of expectation. Not bad. If someone bothers to look at my Fuelly and sees the huge swings in the graph, reading the profile explains it.
The most significant figure in Fuelly for me is "Total Spent" and cost per mile.THAT is the #1 blow-mind stat for my truck.
Adding a "What percentage of tank miles were towing?" option would be helpful. Likewise, many parts of the USA have elevations well above sea-level. Altitude and mountain passes are hard on mileage too. Perhaps another profile based option about "average altitude" or "home altitude" may help some folks too.
I use the site to find out the MPG of any car I consider buying, and I am sure many others do also, throwing in towing MPG numbers will skew the avg car data. It would be nice to have a separate category for towing mpg to keep the actual mpg numbers clean. For example, some diesel trucks get 20 mpg (not loaded) while others get 14 mpg, depending on the year and make, when looking for a used truck mpg can be a major consideration.
True small diesel trucks can get great mileage. In the U.S. many people buy large diesels specifically to tow their recreational vehicles around full time when retired, the trailers typically weigh from 12,000lbs to 18,000lbs, when the mpgs get in the real low numbers the difference between a truck that gets 8mpg towing and 15 mpg towing can be huge! With diesel near $4 a gallon that is the difference between $500 vs $266 for a 1000 mile trip, and this type of mileage is common for retirees who come to the warmer areas of the states during the winter months. The thing is depending on the make and year of diesel truck you will see wild variations in MPG, I know I specifically looked for one that had excellent mpg ratings, returning 20 mpg for an 8500 lb vehicle unloaded and 15.5 towing.. Of course trailer aerodynamics affect the mpg also, my 5th wheel trailer is low profile.
You're lucky fuel is still so cheap. A freind of mine drives a Mercedes van that gets 30 MPG, since 2006 he's spent the equivelent of $255,000 just of fuel. Thats one guy in one small van which is not bad on fuel, fuel costs are crippling here and the big haulage companies struggle. It also has a knock on effect for eveything delivered, especialy food.
That is a ridiculous amount of money to spend on fuel! I like the slow re-emergence of bicycling that is regaining popularity in Europe. cargo bikes and Velomobiles especially. With electric assist bicycles just now gaining popularity most of the commutes a plug in hybrid could make on pure electric could probably be done on an E-bike.