I am not sure of the amount/percentage, but I wonder how much is impacted by the fuel density. I would think that a motorcycle may have more variability since the fuel tank is so exposed to heat from the sun and from the engine. Perhaps this also impacts the number of miles you get per gallon since a gallon of volume may have more or less "energy" due to the density changing from temperature.
I wasn't trying to disparage your record keeping. I thought I was making a cute remark but if you took it differently I apologize. Sometimes it look different in print.
Have fun and be safe.
On Friday I went through 3 tanks of fuel for the sake of riding (and a day away from work).
Tank #1 157.8 miles on 4.864 gal = 32.5 MPG, overall average speed 61 MPH
Tank #2 161.9 miles on 4.539 gal = 35.7 MPG, overall average speed 62 MPH
Tank #3 206.3 miles on 5.181 gal = 40 MPG, overall average speed 66 MPH
You will see that on any given day, and any given tank of fuel, the MPG can vary greatly. I contribute most of this fluctuation to the wind, which was ~ 15 MPH out of the WNW, which caused a direct headwind for all of tank #1 and 1/2 of tank #2. It also became a tailwind for the second half of the ride. I set my cruise control on 74 MPH by the GPS (~78 MPH on the speedo) for most of the trip, except for some populated areas, and one strech of 20 mile 2-lane on the last tank. My bike has averaged 37.2 MPG over the life of it.
It's nice to keep track of your tank to tank mpg in an organized fasion so you have a good idea what your bike usually does, and how it behaves under differing conditions. I like to ride tank to tank, so this is even more relevant to me, but should be something everyone tracks to help record the health of your ride. It's also nice to know even when you're puttering around in the middle of nowhere and decide to fuel up in a one-horse town, only to find that they only sell 85 octane gas. Do you have the range to make it to the next town? I could tell you that my decision wouldn't be a guess.
My 2010 FLHTK has only 600 miles on it. I was shocked that the analog fuel gauge was on "E" when I had 2 gallons left. so my "e" really means one third tank remaining. That puts my bike right in line with user dbinbc. I haven't tested out the "r" factor yet.I had the sender unit inside the tank and the gauge replaced. I would be at about half tank based on what it took to fill it back up, but my low fuel light would be on and the gauge would still be at full. Now with things replaced my gauge hits E while I still have about 1/3 tank left. I can live with that. r reading seems to be fairly close. My ride is an '09 FLHTC and with 3500 kilometres (about 2100 miles) I'm finally up to about 50 Imperial mpg (41.5 US mpg). Hoping it will get better because my '07 got almost 10 mpg more.
On Friday I went through 3 tanks of fuel for the sake of riding (and a day away from work).
Tank #1 157.8 miles on 4.864 gal = 32.5 MPG, overall average speed 61 MPH
Tank #2 161.9 miles on 4.539 gal = 35.7 MPG, overall average speed 62 MPH
Tank #3 206.3 miles on 5.181 gal = 40 MPG, overall average speed 66 MPH
74 MPH by the GPS (~78 MPH on the speedo)