For the past few months (and 5000 miles) my ST has been averaging a solid 42 miles per gallon. Some tanks net a bit more between fill-ups, some a bit less, but their combined average is right at 42mpg. Three of those tanks have netted less than 36 mpg. One less than 33 mpg.
I usually let the tank run about 3/4 of the way down to near empty (and into the flashing bar) between fill-ups, with somewhere between 250-300 miles per tank. When I do put gas in it, I always fill it up. There have only been a few times - three to be exact - where I filled a mostly full tank, with about 100 miles or less on the bike since my last fill up.
I should add that I do the math the old fashoned way, with a pencil & paper. The fuel consumption average-o-meter on the bike is next to useless, and while the speedometer & odometer are generous in their numbers, they are consistent, which is key. That consistency is reflected when I fill up by filling the tank to the same point every time with the bike on the center stand. To take it one step further, most of my fill-ups have been at the same pump at the same station. (That may actually be an OCD.)
The thing I found interesting was that the three tanks that netted my worst mileage were the same three tanks where I hadn't gone very far between fill-ups. The tanks where I've netted the best mileage were tanks that I ran nearly dry, whether commuting or riding on longer day trips.
My riding style doesn't change from fill-up to fill-up. I certainly haven't changed it to see if riding slow vs. faster changes the mpg; I just ride it. I also haven't been riding with it loaded down one day and unloaded the next, or spent large amounts of time with the windscreen all the way up instead of down. The only thing that changed was the amount of fuel still remaining in the tank at fill-up time. Granted, this bike is still relatively new, with only 5500+ miles, and three tanks of fuel (out of 23) really isn't a lot to make a good comparison, but it seems like the ST gets poor mileage when the tank is full, and that the mileage gets better as the tank drains. This is only an assumption, but since the bike is averaging 42 mpg overall, I don't know what else to make of it. I know that a gallon of fuel weighs more than a few pounds, but I can't see the weight difference between 7.5 gallons and 1.5 gallons making a lot of difference to the 1300cc mill in the ST.
What a difference a year makes! - Last winter we had what us long-time locals would describe as a "20-year weather event." It snowed... and it snowed and snowed! Enough to collapse roofs ...
5 days ago