I fill up after hitting reserve usually around the 135 mile mark, averaging 3.6 gallons. But should I fill up at the 100 mile mark I'm looking at 2.4 to 2.7 gallons depending on which bike I'm on and how hard I'm riding.
When I ride Vera Hard I get 35mpg. Ride her soft and I'm looking at 40mph. Cinnamon Girl likewise is 36/46. Yes CG does get better overall gas mileage.
To answer your question if you could get more than another 40-50 miles on the other approx. 2.4 gal left in the tank: Yes! Given that you are getting 50 mpg, you should use 140 on your tip odometer before you fill up, end even then, you won't be on reserve.
The 100 mile mark is more a function of monkey butt prevention on slab rides than it is a need to refuel. On rural roads the 100 miles mark is usually interspersed with several stops, so no need to stop for rear end reasons. However, at slab speeds, the 100 mile mark usually means speeds at 75+ mph. After a couple of tank to tank segments (at least 20 miles past reserve before fill up), that 100 mile mark may well even migrate down to 75 then 50.
